Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass

Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Short Report Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass Maris Kruuse, Ants Tull, Harri Valdmann This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6328232/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Sep, 2025 Read the published version in European Journal of Wildlife Research → Version 1 posted 8 You are reading this latest preprint version Abstract Wildlife passages aim to improve connectivity between habitats fragmented by heavily trafficked roads. However, their effectiveness must be monitored. Kolu ecoduct, Estonia’s first wildlife overpass, was built in 2013 during the reconstruction of the Aruvalla-Kose section of the T2 (E263) road. To evaluate its usage, we analyzed camera trap data from two periods: initial monitoring (March 12, 2015 – October 31, 2016), which recorded 1,585 crossings, and follow-up monitoring (November 6, 2020 – October 25, 2022), which recorded 1,308 crossings. Over this period, the distribution of mammal species using the overpass changed significantly. The proportion of domestic animal crossings declined from 36–9.4%, while large game crossings increased from 19–58%. Small game crossings slightly decreased from 37–31%. Unidentified crossings dropped from 3.6–0.5%. Human presence was rare, decreasing from 4.2% in the initial period to just 0.2% in the follow-up monitoring. wildlife overpass monitoring camera trap mammals road ecology Figures Figure 1 Figure 2 Introduction Balancing human mobility with ecological connectivity is crucial for sustainable transport infrastructure (Trombulak and Frissell 2000 ; Forman et al. 2003 ; Benítez-López et al. 2010 ). Roads with traffic exceeding 10,000 vehicles per day pose a significant barrier to wildlife and increase mortality risk during crossing attempts (Seiler et al. 2023 ). Such roads are often fenced to improve traffic safety, forming complete barriers for most animals. To mitigate these effects, it is necessary to identify important wildlife movement corridors and construct crossing structures at suitable locations (van der Ree et al. 2015 ). In Estonia, crossing structures, including wildlife overpasses, are increasingly used to minimize the impact of roads and enhance traffic safety. However, the evidence base for evaluating the effectiveness of these structures remains limited (Soanes et al. 2024 ). We aimed to provide further evidence supporting the hypothesis that large mammals exhibit a “learning curve” when using crossing structures, leading to increased crossing frequency over time (Barrueto et al. 2014 ; Mysłajek et al. 2020 ). Materials and Methods Kolu wildlife overpass is located in Kose Parish, Northern Estonia (N 59.18785, E 25.06043). The area consists of forests, fields, and grasslands forming a green corridor suitable for moose ( Alces alces ) crossings where the Kolu overpass was constructed. The overpass was built in 2013 as part of the reconstruction of Aruvalla-Kose section of the T2 (E263) Tallinn-Tartu-Võru-Luhamaa road. It spans a 22 m wide corridor over a four-lane highway, featuring sound barriers and vegetation to encourage wildlife use. Traffic intensity on this section increased by over a third from 2014 (10,000 vehicles/day) to 2022 (13,545 vehicles/day) (Kaal et al. 2015 ; Estonian Transport Administration 2023 ). The initial monitoring of animal crossing events on Kolu overpass started in 2015, approximately one year after construction, and lasted 22 months. Weekly observations included track identification and analysis of camera trap data. Two infrared-triggered Uovision UM565-SMS GPRS 12 MP trail cameras were placed on both ends of a sand strip in the middle of the overpass. The follow-up monitoring period, lasting 25 months from 2020 to 2022, we used three infrared-triggered Willfine 4G cameras placed on the sand strip. Track observations were conducted monthly as supplementary data but were not included in the current analysis. Each recorded crossing event included date, time, species, number of individuals, crossing direction, and additional behavioral observations. Duplicate detections from multiple cameras were excluded from the analysis. Parametric two-proportion z-tests were applied to find differences between larger game, smaller game or domestic animal groups (large game, small game and domestic animals) between two time periods. The method defines successes (number of animal crossings) and failures (non-target species crossings) and computes the total observations for each period by adding successes and failures. Non-parametric Mann-Whitney U tests were used to compare roe deer crossings between months of the two monitoring periods. All statistical tests were carried out in R (ver. 4.1.3, R Development Core Team 2022). Results and Discussion During the initial monitoring in 2015–2016, we observed presence of 12 wild mammal species, including large game – roe deer ( Capreolus capreolus ), wild boar ( Sus scrofa ), grey wolf ( Canis lupus ) and Eurasian lynx ( Lynx lynx ); small game – red fox ( Vulpes vulpes ), raccoon dog ( Nyctereutes procyonoides ), European hare ( Lepus europaeus ), mountain hare ( Lepus timidus ), pine marten ( Martes martes ) and European badger ( Meles meles ); also European hedgehog ( Erinaceus europaeus ) and red squirrel ( Sciurus vulgaris ). Among domestic animals, cats and dogs were recorded (Valdmann and Kruuse 2016 ). During the follow-up monitoring period in 2020–2022, a total of 14 wild mammal species were identified, including all Estonian ungulates (moose, red deer ( Cervus elaphus ), roe deer and wild boar) and large carnivores – lynx and brown bear ( Ursus arctos ). Among the smaller mammals red fox, badger, raccoon dog, European and mountain hare, pine marten, hedgehog and a unidentified bat ( Chiroptera ) were recorded. Also, cats and dogs were present (Valdmann et al. 2022 ) (Table 1 ). Table 1 Number of different species` crossings on Kolu wildlife overpass during the initial and follow-up monitoring period; 600 and 719 days, respectively Classification Species 2015–2016 2020–2022 Total Large game Capreolus capreolus 144 728 872 Large game Sus scrofa 143 4 147 Large game Alces alces 0 23 23 Large game Cervus elaphus 0 3 3 Large game Canis lupus 10 0 10 Large game Lynx lynx 0 5 5 Large game Ursus arctos 0 1 1 Small game Vulpes vulpes 483 314 797 Small game Nyctereutes procyonoides 89 33 122 Small game Meles meles 1 45 46 Small game Lepus europaeus, Lepus timidus 15 12 27 Small game Martes martes 2 6 8 Small mammal Erinaceus europaeus 3 1 4 Domestic animal Felis catus 521 114 635 Domestic animal Canis lupus familiaris 50 9 59 Unidentified Unidentified 57 7 64 Human Human 67 3 70 Total 1585 1308 2893 Analysis of the two monitoring periods revealed significant changes in species composition and crossing frequencies. The proportion of large game crossings increased from 19–58% ( p < 0.001; χ² = 453; 95% CI -0.42 to -0.36 ), while domestic animal crossings declined from 36–9.4% ( p < 0.001; χ² = 299; 95% CI 0.38 to 0.31). Small game crossings slightly decreased from 37–31% ( p < 0.01; χ² = 17; 95% CI 0.04 to 0.1; Fig. 1 ). In both monitoring periods, roe deer crossings dominated among large game (49% and 95%, respectively). The monthly comparison (first period months vs second period months) indicated that roe deer crossings increased significantly (p < 0.001) except in March (p = 0.8, Fig. 2 ). Crossings peaked in May, likely related to fawning or establishing home ranges. Roe deer territorial markings on the overpass were first time registered only during follow-up monitoring period. This suggests that for follow-up monitoring period roe deer had successfully adapted to using the overpass. Wild boar crossings declined sharply most likely due to population collapse from African swine fever (ASF) and intensified hunting pressure (Kruuse et al. 2016 ). Given that ASF caused a dramatic decline in wild boar numbers across Estonia, their reduced presence on the overpass aligns with national population trends (Estonian Environment Agency 2024 ). However, a positive finding in follow-up monitoring period were the observations of moose as many as 23 crossings, red deer, and brown bear, which were not observed during the initial monitoring. Probably the height growth of deciduous trees like grey alder ( Alnus incana ) and shrubs like willow ( Salix spp. ) exceeding two meters has facilitated increased movement of large game on Kolu ecoduct. Moose numbers during study period in Estonia have been quite stable or even decreasing, thus not contributing into increased crossing numbers (Estonian Environment Agency 2024 ). Among small game species, red fox and raccoon dog crossings declined significantly. This decline may be linked to sarcoptic mange outbreaks, which are known to periodically reduce canid populations (Escobar et al. 2021 ). However, badger crossings increased, which corresponds with the species’ growing population in Estonia. Vegetation growth on the overpass likely influenced species behavior. Over time, deciduous trees and shrubs have grown, providing better cover. Studies suggest that well-vegetated overpasses encourage use by large mammals (Rosell et al. 2023 ). The minimal human presence (0.2% in the follow-up monitoring) also likely supports greater wildlife use (Denneboom et al. 2021 ). These results are consistent with findings from previous studies, where long-term monitoring has shown increasing wildlife adaptation to crossing structures (Soanes et al. 2024 ). Importantly, wildlife crossings in addition to contributing to ecological connectivity also support wildlife and ecosystems in adapting to climate change (Littlefield et al. 2024 ). However, species-specific responses vary, indicating that continued monitoring is necessary to evaluate long-term ecological impacts. Conclusions The follow-up monitoring of the Kolu ecoduct demonstrates that large mammals, particularly roe deer, have increasingly adapted to using the structure. The overpass’s naturalization over time and minimal human disturbance have most likely contributed to its success as shown by moose and bear crossings during the second monitoring period. The decline of wild boar numbers is obviously caused by ASF, which is widespread in Estonia. However, certain small game species also showed a decline in crossings, indicating the need for ongoing monitoring to assess long-term ecological impacts. These findings highlight the importance of adaptive management in wildlife mitigation strategies. Declarations Funding Declaration This research was funded by Estonian Transport Administration through the projects “Monitoring the Performance of Wildlife Mitigation Measures on Main Road 2, Tallinn-Tartu-Võru-Luhamaa, Aruvalla-Kose Section” (contract 15–00242/015) and “Monitoring the Performance of the Kolu and Kohatu Ecoducts and Related Wildlife Facilities” (contract 1–12/20/1920-1), conducted by the Estonian Naturalists’ Society. Author Contribution All authors contributed to the study conception and design. Fieldworks, data collection and dataset preparation were carried out by MK, AT and HV and descriptive analysis were performed by MK and AT. Statistical analysis were performed by AT. The first draft of the manuscript was written by MK. All authors provided critical feedback and approved the final version. Acknowledgement We thank the Estonian Transport Administration for initiating and funding this research. Data Availability Datasets generated in this study are stored in Estonian Transport Administration and the authors and will be made available upon request. References Barrueto M, Ford AT, Clevenger AP (2014) Anthropogenic effects on activity patterns of wildlife at crossing structures. Ecosphere 5(3):1–19. https://doi.org/10.1890/ES13-00382.1 Benítez-López A, Alkemade R, Verweij PA (2010) The impacts of roads and other infrastructure on mammal and bird populations: A meta-analysis. Biol Conserv 143(6):1307–1316. https://doi.org/10.1016/j.biocon.2010.02.009 Denneboom D, Bar-Massada A, Shwartz A (2021) Factors affecting usage of crossing structures by wildlife – A systematic review and meta-analysis. Sci Total Environ 777:146061. https://doi.org/10.1016/j.scitotenv.2021.146061 Escobar LE, Carver S, Cross PC et al (2021) Sarcoptic mange: an emerging panzootic in wildlife. Transbound Emerg Dis 69(3):927–942. https://doi-org.ezproxy.utlib.ut.ee/ 10.1111/tbed.14082 Estonian Environment Agency (2024) Ulukiasurkondade seisund ja küttimissoovitus 2024. (Status of Game populations in Estonia and proposal for hunting in 2024. In Estonian). Available at https://keskkonnaportaal.ee/sites/default/files/SEIREARUANNE_2024.pdf . Accessed 27 March 2025 Estonian Transport Administration (2023) 2022. aasta riigiteede liiklussageduste andmed. (Traffic data for national roads in 2022. In Estonian) Forman RTT et al (2003) Road ecology: science and solutions. Island, Washington, DC, USA Kaal L et al (2015) Liiklusloenduse tulemused 2014. aastal. (Results of traffic counts in 2014. In Estonian). AS Teede Tehnokeskus Kruuse M, Enno S-E, Oja T (2016) Temporal patterns of wild boar-vehicle collisions in Estonia, at the northern limit of its range. Eur J Wildl Res 62(6):787–791. https://doi.org/10.1007/s10344-016-1042-9 Littlefield CE, Suraci JP, Kintsch J, Callahan R, Cramer P, Cross MS, Dickson BG, Duncan LA, Fisher JR, Freeman PT, Seidler R, Wearn A, Andrews KM, Brocki M, Dodd N, Gagnon J, Johnson A, Krosby M, Skroch M, Sutherland R (2024) Evaluating and elevating the role of wildlife road crossings in climate adaptation. Front Ecol Environ e2816. https://doi.org/10.1002/fee.2816 Mysłajek RW, Olkowska E, Wronka-Tomulewicz M et al (2020) Mammal use of wildlife crossing structures along a new motorway in an area recently recolonized by wolves. Eur J Wildl Res 66:79. https://doi.org/10.1007/s10344-020-01412-y R Core Team (2022) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.r-project.org/ Rosell C et al (2023) Solutions to mitigate impacts and benefit nature. In: C. Rosell., (Eds.) 2023. IENE Biodiversity and infrastructure. A handbook for action. https://www.biodiversityinfrastructure.org/ . Accessed 3 October 2024 Seiler A, Guinard E, Mot R (2023) Ecological effects of Infrastructure. In: C. Rosell (Eds.) 2023. IENE Biodiversity and infrastructure. A handbook for action. https://www.biodiversityinfrastructure.org/ . Accessed 3 October 2024 Soanes K, Rytwinski T, Fahrig L, Huijser MP, Jaeger JAG, Teixeira FZ, van der Ree R, van der Grift EA (2024) Do wildlife crossing structures mitigate the barrier effect of roads on animal movement? A global assessment. J Appl Ecol 61(3):417–430. https://doi.org/10.1111/1365-2664.14582 Trombulak SC, Frissell CA (2000) Review of Ecological Effects of Roads on Terrestrial and Aquatic Communities. Conserv Biol 14:18–30. https://doi.org/10.1046/j.1523-1739.2000.99084.x Valdmann H, Erimäe R, Erimäe J, Tull A, Kruuse M (2022) Kolu ja Kohatu ökoduktide ning nendega seotud ulukirajatiste toimivuse seire lõpparuanne. (Monitoring the performance of the Kolu and Kohatu ecoducts and related wildlife facilities. Final report. In Estonian). Estonian Naturalists` Society. Available at https://transpordiamet.ee/sites/default/files/documents/2023-02/Kolu_Kohatu_seire_l%C3%B5pparuanne_sh_V_etapp_nov_2022.pdf . Accessed 10 June 2024 Valdmann H, Kruuse M (2016) Põhimaantee 2 Tallinn-Tartu-Võru-Luhamaa Aruvalla-Kose lõigu ulukirajatiste, sh Kuusiku ökodukti seire lõpparuanne. (Monitoring the performance of wildlife mitigation measures on main road 2, Tallinn-Tartu-Võru-Luhamaa, Aruvalla-Kose section. Final report. Estonian). Estonian Naturalists` Society van der Ree R, Smith J, Grilo C (eds) (2015) Handbook of Road Ecology. Wiley Blackwell, Oxford Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 16 Sep, 2025 Read the published version in European Journal of Wildlife Research → Version 1 posted Editorial decision: Revision requested 28 Jul, 2025 Reviewers agreed at journal 21 May, 2025 Reviews received at journal 19 May, 2025 Reviewers agreed at journal 19 May, 2025 Reviewers invited by journal 16 May, 2025 Editor assigned by journal 02 May, 2025 Submission checks completed at journal 02 May, 2025 First submitted to journal 28 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6328232","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":458866554,"identity":"b0def47a-35b9-4fff-8b96-64275af75e65","order_by":0,"name":"Maris Kruuse","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFElEQVRIiWNgGAWjYJCCAwwMCRDWByCWALMMiNTCOAOogygtDDAtzDxwLXiAbvvZhwd/MKTlG9xIf/jYNsemTrKB+fHrigIGOX4cWszOpBsc5mHIsdxwI8fYOHdbmoQ0A5uZ5RkDBmPJBhxaDqQxHGZgqDAwuJHDJp277bCEHFDQsMGAIXHDARxazj9jADoMpCX9+W/Lbf+BWti/gbTU78el5UYawwGgw4BaEsyYGbcdADqMx/ghUEsCrkAzu/GM4TCPQZqB5Jk3xpK925IlZzbzlDE2GEgYzsDpsDTmjz8qkg34jqc//PBzmx2/xPH2zR8b/tjI8+PwPgSguIGZgU0ClgiIBswfSFM/CkbBKBgFwxwAANA2VoawE1hVAAAAAElFTkSuQmCC","orcid":"","institution":"Centre of Estonian Rural Research and Knowledge","correspondingAuthor":true,"prefix":"","firstName":"Maris","middleName":"","lastName":"Kruuse","suffix":""},{"id":458866555,"identity":"d73b0f26-09f7-49b2-86c8-8c35a7ef7d4d","order_by":1,"name":"Ants Tull","email":"","orcid":"","institution":"University of Tartu","correspondingAuthor":false,"prefix":"","firstName":"Ants","middleName":"","lastName":"Tull","suffix":""},{"id":458866557,"identity":"43458a38-faaa-40ce-a48e-3d642dda3ca0","order_by":2,"name":"Harri Valdmann","email":"","orcid":"","institution":"University of Tartu","correspondingAuthor":false,"prefix":"","firstName":"Harri","middleName":"","lastName":"Valdmann","suffix":""}],"badges":[],"createdAt":"2025-03-28 12:38:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6328232/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6328232/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10344-025-01996-3","type":"published","date":"2025-09-16T15:57:17+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83121423,"identity":"c4ce1ae4-90b4-475b-bfad-b2c1f21f04a7","added_by":"auto","created_at":"2025-05-20 08:59:11","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":54299,"visible":true,"origin":"","legend":"\u003cp\u003eProportions of different animal and human crossings on Kolu wildlife overpass during the initial and follow-up monitoring periods.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6328232/v1/6371bc068f8ad7c8e0f1488a.jpeg"},{"id":83121422,"identity":"151cdaca-1acc-490d-a1b2-1ef235d88c4c","added_by":"auto","created_at":"2025-05-20 08:59:11","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":92560,"visible":true,"origin":"","legend":"\u003cp\u003eRoe deer crossings on the Kolu overpass during the initial monitoring period (March 12, 2015 – October 31, 2016) and follow-up monitoring period (November 6, 2020 – October 25, 2022).\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6328232/v1/11e24a12c16e979a9fb7705a.jpeg"},{"id":91889785,"identity":"486b1ed1-882a-4139-bbf2-85440551335a","added_by":"auto","created_at":"2025-09-22 16:01:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":560704,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6328232/v1/8ae2c7f3-eb2e-46fb-a6ac-4e37cd2e2f4a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBalancing human mobility with ecological connectivity is crucial for sustainable transport infrastructure (Trombulak and Frissell \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Forman et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Ben\u0026iacute;tez-L\u0026oacute;pez et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Roads with traffic exceeding 10,000 vehicles per day pose a significant barrier to wildlife and increase mortality risk during crossing attempts (Seiler et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Such roads are often fenced to improve traffic safety, forming complete barriers for most animals. To mitigate these effects, it is necessary to identify important wildlife movement corridors and construct crossing structures at suitable locations (van der Ree et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn Estonia, crossing structures, including wildlife overpasses, are increasingly used to minimize the impact of roads and enhance traffic safety. However, the evidence base for evaluating the effectiveness of these structures remains limited (Soanes et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). We aimed to provide further evidence supporting the hypothesis that large mammals exhibit a \u0026ldquo;learning curve\u0026rdquo; when using crossing structures, leading to increased crossing frequency over time (Barrueto et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Mysłajek et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eKolu wildlife overpass is located in Kose Parish, Northern Estonia (N 59.18785, E 25.06043). The area consists of forests, fields, and grasslands forming a green corridor suitable for moose (\u003cem\u003eAlces alces\u003c/em\u003e) crossings where the Kolu overpass was constructed. The overpass was built in 2013 as part of the reconstruction of Aruvalla-Kose section of the T2 (E263) Tallinn-Tartu-V\u0026otilde;ru-Luhamaa road. It spans a 22 m wide corridor over a four-lane highway, featuring sound barriers and vegetation to encourage wildlife use.\u003c/p\u003e \u003cp\u003eTraffic intensity on this section increased by over a third from 2014 (10,000 vehicles/day) to 2022 (13,545 vehicles/day) (Kaal et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Estonian Transport Administration \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe initial monitoring of animal crossing events on Kolu overpass started in 2015, approximately one year after construction, and lasted 22 months. Weekly observations included track identification and analysis of camera trap data. Two infrared-triggered Uovision UM565-SMS GPRS 12 MP trail cameras were placed on both ends of a sand strip in the middle of the overpass.\u003c/p\u003e \u003cp\u003eThe follow-up monitoring period, lasting 25 months from 2020 to 2022, we used three infrared-triggered Willfine 4G cameras placed on the sand strip. Track observations were conducted monthly as supplementary data but were not included in the current analysis.\u003c/p\u003e \u003cp\u003eEach recorded crossing event included date, time, species, number of individuals, crossing direction, and additional behavioral observations. Duplicate detections from multiple cameras were excluded from the analysis. Parametric two-proportion z-tests were applied to find differences between larger game, smaller game or domestic animal groups (large game, small game and domestic animals) between two time periods. The method defines successes (number of animal crossings) and failures (non-target species crossings) and computes the total observations for each period by adding successes and failures. Non-parametric Mann-Whitney U tests were used to compare roe deer crossings between months of the two monitoring periods. All statistical tests were carried out in R (ver. 4.1.3, R Development Core Team 2022).\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eDuring the initial monitoring in 2015\u0026ndash;2016, we observed presence of 12 wild mammal species, including large game \u0026ndash; roe deer (\u003cem\u003eCapreolus capreolus\u003c/em\u003e), wild boar (\u003cem\u003eSus scrofa\u003c/em\u003e), grey wolf (\u003cem\u003eCanis lupus\u003c/em\u003e) and Eurasian lynx (\u003cem\u003eLynx lynx\u003c/em\u003e); small game \u0026ndash; red fox (\u003cem\u003eVulpes vulpes\u003c/em\u003e), raccoon dog (\u003cem\u003eNyctereutes procyonoides\u003c/em\u003e), European hare (\u003cem\u003eLepus europaeus\u003c/em\u003e), mountain hare (\u003cem\u003eLepus timidus\u003c/em\u003e), pine marten (\u003cem\u003eMartes martes\u003c/em\u003e) and European badger (\u003cem\u003eMeles meles\u003c/em\u003e); also European hedgehog (\u003cem\u003eErinaceus europaeus\u003c/em\u003e) and red squirrel (\u003cem\u003eSciurus vulgaris\u003c/em\u003e). Among domestic animals, cats and dogs were recorded (Valdmann and Kruuse \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). During the follow-up monitoring period in 2020\u0026ndash;2022, a total of 14 wild mammal species were identified, including all Estonian ungulates (moose, red deer (\u003cem\u003eCervus elaphus\u003c/em\u003e), roe deer and wild boar) and large carnivores \u0026ndash; lynx and brown bear (\u003cem\u003eUrsus arctos\u003c/em\u003e). Among the smaller mammals red fox, badger, raccoon dog, European and mountain hare, pine marten, hedgehog and a unidentified bat (\u003cem\u003eChiroptera\u003c/em\u003e) were recorded. Also, cats and dogs were present (Valdmann et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNumber of different species` crossings on Kolu wildlife overpass during the initial and follow-up monitoring period; 600 and 719 days, respectively\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClassification\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2015\u0026ndash;2016\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2020\u0026ndash;2022\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eCapreolus capreolus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e728\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e872\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eSus scrofa\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e143\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e147\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eAlces alces\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eCervus elaphus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eCanis lupus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eLynx lynx\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLarge game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eUrsus arctos\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eVulpes vulpes\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e483\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e314\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e797\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eNyctereutes procyonoides\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e122\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eMeles meles\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eLepus europaeus, Lepus timidus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall game\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eMartes martes\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmall mammal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eErinaceus europaeus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDomestic animal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eFelis catus\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e521\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e635\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDomestic animal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eCanis lupus familiaris\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUnidentified\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnidentified\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHuman\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHuman\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1585\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1308\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2893\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAnalysis of the two monitoring periods revealed significant changes in species composition and crossing frequencies. The proportion of large game crossings increased from 19\u0026ndash;58% (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001; χ\u0026sup2; = 453; 95% CI -0.42 to -0.36 ), while domestic animal crossings declined from 36\u0026ndash;9.4% (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001; χ\u0026sup2; = 299; 95% CI 0.38 to 0.31). Small game crossings slightly decreased from 37\u0026ndash;31% (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01; χ\u0026sup2; = 17; 95% CI 0.04 to 0.1; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn both monitoring periods, roe deer crossings dominated among large game (49% and 95%, respectively). The monthly comparison (first period months \u003cem\u003evs\u003c/em\u003e second period months) indicated that roe deer crossings increased significantly (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) except in March (p\u0026thinsp;=\u0026thinsp;0.8, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Crossings peaked in May, likely related to fawning or establishing home ranges. Roe deer territorial markings on the overpass were first time registered only during follow-up monitoring period. This suggests that for follow-up monitoring period roe deer had successfully adapted to using the overpass.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWild boar crossings declined sharply most likely due to population collapse from African swine fever (ASF) and intensified hunting pressure (Kruuse et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Given that ASF caused a dramatic decline in wild boar numbers across Estonia, their reduced presence on the overpass aligns with national population trends (Estonian Environment Agency \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, a positive finding in follow-up monitoring period were the observations of moose as many as 23 crossings, red deer, and brown bear, which were not observed during the initial monitoring. Probably the height growth of deciduous trees like grey alder (\u003cem\u003eAlnus incana\u003c/em\u003e) and shrubs like willow (\u003cem\u003eSalix spp.\u003c/em\u003e) exceeding two meters has facilitated increased movement of large game on Kolu ecoduct. Moose numbers during study period in Estonia have been quite stable or even decreasing, thus not contributing into increased crossing numbers (Estonian Environment Agency \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong small game species, red fox and raccoon dog crossings declined significantly. This decline may be linked to sarcoptic mange outbreaks, which are known to periodically reduce canid populations (Escobar et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, badger crossings increased, which corresponds with the species\u0026rsquo; growing population in Estonia.\u003c/p\u003e \u003cp\u003eVegetation growth on the overpass likely influenced species behavior. Over time, deciduous trees and shrubs have grown, providing better cover. Studies suggest that well-vegetated overpasses encourage use by large mammals (Rosell et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The minimal human presence (0.2% in the follow-up monitoring) also likely supports greater wildlife use (Denneboom et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThese results are consistent with findings from previous studies, where long-term monitoring has shown increasing wildlife adaptation to crossing structures (Soanes et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Importantly, wildlife crossings in addition to contributing to ecological connectivity also support wildlife and ecosystems in adapting to climate change (Littlefield et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, species-specific responses vary, indicating that continued monitoring is necessary to evaluate long-term ecological impacts.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe follow-up monitoring of the Kolu ecoduct demonstrates that large mammals, particularly roe deer, have increasingly adapted to using the structure. The overpass\u0026rsquo;s naturalization over time and minimal human disturbance have most likely contributed to its success as shown by moose and bear crossings during the second monitoring period. The decline of wild boar numbers is obviously caused by ASF, which is widespread in Estonia. However, certain small game species also showed a decline in crossings, indicating the need for ongoing monitoring to assess long-term ecological impacts. These findings highlight the importance of adaptive management in wildlife mitigation strategies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding Declaration\u003c/h2\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003eThis research was funded by Estonian Transport Administration through the projects \u0026ldquo;Monitoring the Performance of Wildlife Mitigation Measures on Main Road 2, Tallinn-Tartu-V\u0026otilde;ru-Luhamaa, Aruvalla-Kose Section\u0026rdquo; (contract 15\u0026ndash;00242/015) and \u0026ldquo;Monitoring the Performance of the Kolu and Kohatu Ecoducts and Related Wildlife Facilities\u0026rdquo; (contract 1\u0026ndash;12/20/1920-1), conducted by the Estonian Naturalists\u0026rsquo; Society.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Fieldworks, data collection and dataset preparation were carried out by MK, AT and HV and descriptive analysis were performed by MK and AT. Statistical analysis were performed by AT. The first draft of the manuscript was written by MK. All authors provided critical feedback and approved the final version.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank the Estonian Transport Administration for initiating and funding this research.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eDatasets generated in this study are stored in Estonian Transport Administration and the authors and will be made available upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBarrueto M, Ford AT, Clevenger AP (2014) Anthropogenic effects on activity patterns of wildlife at crossing structures. 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Estonian Naturalists` Society\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan der Ree R, Smith J, Grilo C (eds) (2015) Handbook of Road Ecology. Wiley Blackwell, Oxford\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-wildlife-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejwr","sideBox":"Learn more about [European Journal of Wildlife Research](http://link.springer.com/journal/10344)","snPcode":"10344","submissionUrl":"https://submission.nature.com/new-submission/10344/3","title":"European Journal of Wildlife Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"wildlife overpass, monitoring, camera trap, mammals, road ecology","lastPublishedDoi":"10.21203/rs.3.rs-6328232/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6328232/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWildlife passages aim to improve connectivity between habitats fragmented by heavily trafficked roads. However, their effectiveness must be monitored. Kolu ecoduct, Estonia\u0026rsquo;s first wildlife overpass, was built in 2013 during the reconstruction of the Aruvalla-Kose section of the T2 (E263) road. To evaluate its usage, we analyzed camera trap data from two periods: initial monitoring (March 12, 2015 \u0026ndash; October 31, 2016), which recorded 1,585 crossings, and follow-up monitoring (November 6, 2020 \u0026ndash; October 25, 2022), which recorded 1,308 crossings.\u003c/p\u003e \u003cp\u003eOver this period, the distribution of mammal species using the overpass changed significantly. The proportion of domestic animal crossings declined from 36\u0026ndash;9.4%, while large game crossings increased from 19\u0026ndash;58%. Small game crossings slightly decreased from 37\u0026ndash;31%. Unidentified crossings dropped from 3.6\u0026ndash;0.5%. Human presence was rare, decreasing from 4.2% in the initial period to just 0.2% in the follow-up monitoring.\u003c/p\u003e","manuscriptTitle":"Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-20 08:51:06","doi":"10.21203/rs.3.rs-6328232/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-28T09:59:27+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"321146940338012425076957411502320117993","date":"2025-05-21T18:24:01+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-19T11:49:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"16464270292550230043601058174123246113","date":"2025-05-19T06:37:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-16T07:46:18+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-02T04:48:50+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-02T04:46:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Wildlife Research","date":"2025-03-28T12:34:31+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-wildlife-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ejwr","sideBox":"Learn more about [European Journal of Wildlife Research](http://link.springer.com/journal/10344)","snPcode":"10344","submissionUrl":"https://submission.nature.com/new-submission/10344/3","title":"European Journal of Wildlife Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"eecfc117-44f0-4c8c-8dc9-c1a5643b4752","owner":[],"postedDate":"May 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-22T15:59:10+00:00","versionOfRecord":{"articleIdentity":"rs-6328232","link":"https://doi.org/10.1007/s10344-025-01996-3","journal":{"identity":"european-journal-of-wildlife-research","isVorOnly":false,"title":"European Journal of Wildlife Research"},"publishedOn":"2025-09-16 15:57:17","publishedOnDateReadable":"September 16th, 2025"},"versionCreatedAt":"2025-05-20 08:51:06","video":"","vorDoi":"10.1007/s10344-025-01996-3","vorDoiUrl":"https://doi.org/10.1007/s10344-025-01996-3","workflowStages":[]},"version":"v1","identity":"rs-6328232","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6328232","identity":"rs-6328232","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}