First Documented Case of Pseudo-egg Incubation by Coragyps atratus in a Semiarid Environments

First Documented Case of Pseudo-egg Incubation by Coragyps atratus in a Semiarid Environments | 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 First Documented Case of Pseudo-egg Incubation by Coragyps atratus in a Semiarid Environments André Barbosa Reis, João Pedro Santos de Souza Gonçalves, Thiago Nascimento Zanetti This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6522153/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 11 You are reading this latest preprint version Abstract Inanimate objects, known as pseudo-eggs, have been observed in the nests of various bird species, often being incubated as if they were real eggs. This study presents the first documented case of pseudo-egg incubation by Coragyps atratus , observed in the semi-arid region of Paraíba, Brazil, where an individual treated a mollusk shell as an egg, displaying nesting behavior and aggression toward potential predators. The vulture's presence at the site for over a month coincided with the species' average incubation period, suggesting a significant behavioral interaction with the object. This report expands knowledge on bird-pseudo-egg interactions and underscores the need for further studies to understand the underlying factors driving such behaviors. Nesting behavior Inanimate objects Incubation period Behavioral interaction Bird-pseudo-egg interactions Figures Figure 1 Introduction Strange objects have been observed in nests of different bird species worldwide, especially those that nest on the ground (Conover, 1985; Mellink, 2002). These inanimate objects are pseudo-eggs (Conover, 1985), regarded by the birds as their own and incubated either alone or alongside real eggs (Schoombie and Schoombie, 2017). The exact cause of the presence of pseudo-eggs in nests is unknown; however, three main hypotheses, or a combination thereof, may lead birds to incubate inanimate objects (Schoombie and Schoombie, 2017). The first hypothesis is the incubation stimulus, initially investigated by Coulter (1980), which suggests that species adapted to an "ideal" clutch size adjust less frequently in the nest, leading to a shorter incubation period and consequently greater reproductive success. Thus, the presence of an optimal clutch size seems to lead to a better incubation stimulus, which could trigger the appearance of pseudo-eggs in nests, a case observed mainly in gulls (Beer, 1961; Beer, 1965; Baerends et al., 1970; Coulter, 1980). The second hypothesis is the mistaken egg, when objects with similar colors, shapes, and sizes nearby are dragged into the nest (Conover, 1985). The third is the mistaken food hypothesis, where birds regurgitate some object into their own nest and mistake it for an egg (Sugden, 1947; Twomey, 1948). This last hypothesis was observed with the common tern, which does not feed on snails (Power et al., 2018). However, females of this species consume shells during the laying period as a way to replenish lost calcium during eggshell formation (Nisbet, 1997). In cases of shell regurgitation, the female may perceive the object as an egg. Conover (1985) reports that 6.7% of ring-billed gull nests and 1.6% of California gull nests contained inanimate objects. More recently, a grey-headed albatross was observed “manufacturing” its own pseudo-egg made of plant fibers, which perhaps took on a rounded shape and “ideal” size after the bird repeatedly manipulated the material with its beak (Schoombie and Schoombie, 2017). Other records of pseudo-eggs have been documented, such as the long-billed curlew incubating mammal bones (Langlois et al., 2012), a Canada goose with a golf ball (Lee, 1998), and snail or crab shells, and even guano, in the nests of roseate terns and brown boobies (Mellink, 2002; Power et al., 2018). Laysan and black-footed albatrosses are occasionally found incubating objects such as beer cans, light bulbs, or even bricks when nesting near human-altered areas (Bartholomew and Howell, 1964; Grant, 1982). The black vulture ( Coragyps atratus ), widely distributed across the Americas, is particularly studied for its reproductive behavior adapted to anthropogenic environments. The reproductive cycle of this species involves a series of specific behaviors that ensure its reproductive success, from mating to parental care. Mating occurs mainly in open areas, where males perform visual and auditory displays to attract females (Baidoo, 2024). After pair formation, nesting generally occurs in natural cavities, such as tree hollows, cliff crevices, or even in abandoned human-made structures (Monsalvo et al., 2020). Unlike many birds, the black vulture does not construct an elaborate nest, preferring bare surfaces for egg-laying (Rush and Naveda-Rodríguez, 2024). The clutch usually consists of one to three eggs, which are whitish with brown spots, providing natural camouflage in the nesting environment. Both parents cooperate during incubation, a critical behavior for protecting the eggs from predators and adverse conditions (Rabenold, 1986; Parker et al., 1995). Both the male and female participate in incubating the eggs, which lasts approximately 32 to 39 days (Coleman and Fraser, 1987). The reproductive behavior of black vultures, adapted to a wide variety of environments, including anthropogenic ones, was also observed under natural conditions during a field trip. Methods On the morning of December 3, 2023, a birdwatching excursion was conducted along a busy dirt road in the municipality of Pocinhos (-7.07745, -36.05986), in the interior of the state of Paraíba, Northeastern Brazil. The region features hyperxerophilic caatinga vegetation, typical of the Brazilian semi-arid environment, characterized by sparse shrubs and large areas of exposed soil, with nearby human settlements. The excursion, which started around 6 a.m., was marked by the sighting of a black vulture on the roadside. The bird displayed a tame demeanor, allowing close approach and not being intimidated by the constant flow of vehicles. During the initial encounter, several photographs of the vulture were taken. A few hours later, around 8:29 a.m., the same vulture was observed again on the ground near the empty shell of a mollusk of the genus Megalobulimus , which was pink in color. The vulture moved towards the shell, a behavior initially interpreted as a search for food remains. However, an unusual behavior was observed, in which the vulture appeared to treat the shell as an egg, displaying signs of nesting (Fig. 1 ). During the observation, a local resident reported that the bird had been present in the area for at least a week and was fending off dogs that tried to approach. About a month after the event, a team member returned to the site and found that the vulture was still there, although they did not have a camera to document new images. Two days later, upon returning with photographic equipment, the vulture was no longer present. Results Among the hypotheses presented, it was not possible to fully fit the vulture's behavior into any one of them, as we could not determine the shell's history before being used by the bird. Furthermore, it is crucial to gather more records similar to the one described, as only by fully monitoring the individual’s routine and interaction with the pseudo-egg can we understand the origin and primary reason for this behavior. As a result, we were able to document a previously unreported behavior for the species, Coragyps atratus , thus expanding the current knowledge about its behavioral repertoire and ecological interactions. This novel observation highlights the importance of detailed field studies in unveiling unexpected aspects of species' life histories. Discussion The vulture's stay in the area for just over a month coincides with the species’ incubation period, further suggesting the bird's attempt to incubate the pseudo-egg, along with its aggressive behavior towards potential predators. It is important to highlight the account of Murphy, a 31-year-old bald eagle ( Haliaeetus leucocephalus ), observed caring for a rock as if it were an egg at the World Bird Sanctuary in Missouri (RFS website). This behavior is the most similar to the observed vulture behavior found in the literature. Moreover, it is worth noting that the behavior of many animals in captivity may differ significantly from what is seen in their natural habitat, due to factors such as the absence of environmental stimuli, social interactions, and hunting opportunities (Morgan and Tromborg, 2007). Conclusion Thus, we contribute here the first documented record of pseudo-egg incubation by vultures. This report opens up avenues for new studies investigating bird species and the factors leading to the incubation of inanimate objects as eggs. Lastly, we emphasize the importance of birdwatching practices by the public and the deposit of these records in citizen science platforms, allowing researchers to make new discoveries and conduct further studies. Declarations Acknowledgements I am deeply grateful to my birdwatching groups, 'Caatingueiros' and 'Jaquinhas de Gargaú,' as it was during a field trip with members of these groups that I had the opportunity to witness the unusual behavior of a vulture incubating a shell. I would also like to express my gratitude to my friends João Pedro and Thiago Zanetti, who accepted the invitation to co-author this scientific note with me. Thank you all very much. Conflict of interest statement We can confirm that the authors have no conflicts of interest to declare. Funding This research received no external funding. References Baerends, G. P., Drent, R. H., Glas, P. & Groenewold, H. 1970. An ethological analysis of incubation behaviour in the Herring Gull. Behaviour 17(Suppl.): 135–235. Baidoo, K. 2024. Agonistic Interactions and Tail-cocking Posture in the Black Vulture ( Coragyps atratus ). (Senior thesis). Princeton University. Bartholomew, G.A. & Howell,T. R. 1964. Experiments on nesting behaviour of Laysan and Black-footed albatrosses. Animal Behaviour 12: 549–558. Beer, C. G. (1961). Incubation and nest building behaviour of Black-headed Gulls. 1: Incubation behaviour in the incubation period. Behaviour 18: 62–105. Beer, C. G. 1965. Clutch size and incubation behaviour in Black-billed Gulls (Larus bulleri). Auk 82: 1–18. Coleman, J. S., & Fraser, J. D. (1987). Food habits of Black and Turkey vultures in Pennsylvania and Maryland. The Journal of wildlife management , 733-739. Conover, M.R. (1985) Foreign Objects In Bird Nests. Auk 102 (4):696–700 Coulter, M.C. (1980) "Stones: an Important Incubation Stimulus for Gulls and Terns," The Auk: Vol. 97: Iss. 4, Article 39. Grant, G. S., Pettit,T. D., Rahn, H.,Whittow, G. C. & Paganelli, C.V. 1982.Water loss from Laysan and Black-footed albatross eggs. Physiological Zoology 55: 405–414. Langlois, L.A., Murböck, K., Bulla, M., Kempenaers, B. (2012) Unusual incubation: Long-billed Dowitcher incubates mammalian bones. Ardea 100:206–210. https://doi.org/10.5253/078.100.0213 Lee, D.L. (1998) 3542. The journal of the Elisha Mitchell Scientific Society 114 (3):163 Mellink, E. (2002). Pseudo-eggs of brown Sula leucogaster and blue-footed S. nebouxii boobies in the Gulf of California, Mexico. Marine Ornithology, 30, 43-44. Monsalvo, J. A., Silva, M. A., Heming, N. M., & Marini, M. Â. (2020). Geographical variation and current knowledge on breeding traits of vultures in the neotropics. Ornithology Research, 28(1), 13-37. Morgan, K. N., & Tromborg, C. T. (2007). Sources of stress in captivity. Applied animal behaviour science, 102(3-4), 262-302. Nisbet, I. 1997. Female Common Terns Sterna hirundo eating mollusc shells: evidence for calcium deficits during egg laying. Ibis 139: 400–401. Parker, P. G., Waite, T. A., & Decker, M. D. (1995). Kinship and association in communally roosting black vultures. Animal Behaviour, 49 (2), 395-401. Power, A., Newton, S., O’connor, I. (2018) Common Terns Sterna hirundo incubating Common Garden Snail shells Helix aspersa on Rockabill Island. Seabird 31:88–91 Rabenold, P. P. (1986). Family associations in communally roosting black vultures. The Auk, 103(1), 32-41. Rush, S. A., & Naveda-Rodríguez, A. (2024). Conspecific nest destruction by black vulture ( Coragyps atratus ). Ornithology Research , 32 (1), 40-43. Schoombie, S. & Schoombie, J. (2017) Pseudo-egg “fabrication” by Grey-headed Albatrosses Thalassarche chrysostoma on Marion Island. SEABIRD 30:71–74 Sugden, J.W. (1947) Exotic Eggs In Nests Of California Gulls. Condor 49:93–96 Twomey, A.C. (1948) The Condor. 5-6. California Gulls And Exotic Eggs. Condor 50 (3):97–100 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 14 Aug, 2025 Reviews received at journal 11 Aug, 2025 Reviews received at journal 04 Aug, 2025 Reviews received at journal 15 Jul, 2025 Reviewers agreed at journal 14 Jul, 2025 Reviewers agreed at journal 10 Jul, 2025 Reviewers agreed at journal 04 Jul, 2025 Reviewers invited by journal 03 Jul, 2025 Editor assigned by journal 08 May, 2025 Submission checks completed at journal 08 May, 2025 First submitted to journal 24 Apr, 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6522153","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":481289614,"identity":"d3597664-6019-47eb-9920-189f1039fcae","order_by":0,"name":"André Barbosa Reis","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIie3RsYrCQBDG8U+ErTzTDkSSV9iQxsdZEVJplcZOQdhKsVV8DCGVxUhAmzxAiiBekzrVYWHhRQ7L1XQH7r8YpvnBwAA22/9MPqZAmzGpN3qfCIWsEQE68j3ibOdJVeHsdZ3shw77woO7vBgJFcd4s0YcChonxGUZoneSRoJ8FLY7UANNX4lbcTqYUWQWfk1uUFPtZCUxp9OXRNYEUEpgJGqi8IoEeRS3FlIFmqKwz1wGunc0Ey8f7nCdKN9fpd85c+E7rjaTv/OeG//+tGHcFNhsNtsHdAcyVUQlzggZ/AAAAABJRU5ErkJggg==","orcid":"","institution":"Universidade Federal Rural de Pernambuco","correspondingAuthor":true,"prefix":"","firstName":"André","middleName":"Barbosa","lastName":"Reis","suffix":""},{"id":481289615,"identity":"f1262625-495a-413c-995e-841d634a53be","order_by":1,"name":"João Pedro Santos de Souza Gonçalves","email":"","orcid":"","institution":"Universidade Federal da Paraíba","correspondingAuthor":false,"prefix":"","firstName":"João","middleName":"Pedro Santos de Souza","lastName":"Gonçalves","suffix":""},{"id":481289616,"identity":"5f88ec52-0ae6-4665-b8fb-b410bb8e3848","order_by":2,"name":"Thiago Nascimento Zanetti","email":"","orcid":"","institution":"Universidade Federal da Paraíba","correspondingAuthor":false,"prefix":"","firstName":"Thiago","middleName":"Nascimento","lastName":"Zanetti","suffix":""}],"badges":[],"createdAt":"2025-04-24 15:23:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6522153/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6522153/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86218315,"identity":"395f0bc1-0f89-4e87-8ffd-2baa26de13cd","added_by":"auto","created_at":"2025-07-08 06:25:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3343725,"visible":true,"origin":"","legend":"\u003cp\u003eInteraction between the black vulture \u003cem\u003eCoragyps atratus\u003c/em\u003e and a mollusk shell of the genus \u003cem\u003eMegalobulimus\u003c/em\u003e, revealing pseudo-egg incubation by the species in a caatinga area of the semi-arid region of Paraíba, Brazil. Photo taken with a Canon SL3 camera and a Canon 75-300mm lens.\u003c/p\u003e","description":"","filename":"figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6522153/v1/0587dbffe322636f0295d49b.png"},{"id":86218327,"identity":"0d0d9b80-ac16-44c0-b8b6-75da80d4b508","added_by":"auto","created_at":"2025-07-08 06:26:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5486168,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6522153/v1/f6d32fa5-d229-4938-95a6-49ee5b3cce1c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"First Documented Case of Pseudo-egg Incubation by Coragyps atratus in a Semiarid Environments","fulltext":[{"header":"Introduction","content":"\u003cp\u003eStrange objects have been observed in nests of different bird species worldwide, especially those that nest on the ground (Conover, 1985; Mellink, 2002). These inanimate objects are pseudo-eggs (Conover, 1985), regarded by the birds as their own and incubated either alone or alongside real eggs (Schoombie and Schoombie, 2017). The exact cause of the presence of pseudo-eggs in nests is unknown; however, three main hypotheses, or a combination thereof, may lead birds to incubate inanimate objects (Schoombie and Schoombie, 2017). The first hypothesis is the incubation stimulus, initially investigated by Coulter (1980), which suggests that species adapted to an \"ideal\" clutch size adjust less frequently in the nest, leading to a shorter incubation period and consequently greater reproductive success. Thus, the presence of an optimal clutch size seems to lead to a better incubation stimulus, which could trigger the appearance of pseudo-eggs in nests, a case observed mainly in gulls (Beer, 1961; Beer, 1965; Baerends et al., 1970; Coulter, 1980). The second hypothesis is the mistaken egg, when objects with similar colors, shapes, and sizes nearby are dragged into the nest (Conover, 1985). The third is the mistaken food hypothesis, where birds regurgitate some object into their own nest and mistake it for an egg (Sugden, 1947; Twomey, 1948). This last hypothesis was observed with the common tern, which does not feed on snails (Power et al., 2018). However, females of this species consume shells during the laying period as a way to replenish lost calcium during eggshell formation (Nisbet, 1997). In cases of shell regurgitation, the female may perceive the object as an egg.\u003c/p\u003e\u003cp\u003eConover (1985) reports that 6.7% of ring-billed gull nests and 1.6% of California gull nests contained inanimate objects. More recently, a grey-headed albatross was observed \u0026ldquo;manufacturing\u0026rdquo; its own pseudo-egg made of plant fibers, which perhaps took on a rounded shape and \u0026ldquo;ideal\u0026rdquo; size after the bird repeatedly manipulated the material with its beak (Schoombie and Schoombie, 2017). Other records of pseudo-eggs have been documented, such as the long-billed curlew incubating mammal bones (Langlois et al., 2012), a Canada goose with a golf ball (Lee, 1998), and snail or crab shells, and even guano, in the nests of roseate terns and brown boobies (Mellink, 2002; Power et al., 2018). Laysan and black-footed albatrosses are occasionally found incubating objects such as beer cans, light bulbs, or even bricks when nesting near human-altered areas (Bartholomew and Howell, 1964; Grant, 1982).\u003c/p\u003e\u003cp\u003eThe black vulture (\u003cem\u003eCoragyps atratus\u003c/em\u003e), widely distributed across the Americas, is particularly studied for its reproductive behavior adapted to anthropogenic environments. The reproductive cycle of this species involves a series of specific behaviors that ensure its reproductive success, from mating to parental care. Mating occurs mainly in open areas, where males perform visual and auditory displays to attract females (Baidoo, 2024). After pair formation, nesting generally occurs in natural cavities, such as tree hollows, cliff crevices, or even in abandoned human-made structures (Monsalvo et al., 2020). Unlike many birds, the black vulture does not construct an elaborate nest, preferring bare surfaces for egg-laying (Rush and Naveda-Rodr\u0026iacute;guez, 2024). The clutch usually consists of one to three eggs, which are whitish with brown spots, providing natural camouflage in the nesting environment. Both parents cooperate during incubation, a critical behavior for protecting the eggs from predators and adverse conditions (Rabenold, 1986; Parker et al., 1995). Both the male and female participate in incubating the eggs, which lasts approximately 32 to 39 days (Coleman and Fraser, 1987). The reproductive behavior of black vultures, adapted to a wide variety of environments, including anthropogenic ones, was also observed under natural conditions during a field trip.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eOn the morning of December 3, 2023, a birdwatching excursion was conducted along a busy dirt road in the municipality of Pocinhos (-7.07745, -36.05986), in the interior of the state of Para\u0026iacute;ba, Northeastern Brazil. The region features hyperxerophilic caatinga vegetation, typical of the Brazilian semi-arid environment, characterized by sparse shrubs and large areas of exposed soil, with nearby human settlements. The excursion, which started around 6 a.m., was marked by the sighting of a black vulture on the roadside. The bird displayed a tame demeanor, allowing close approach and not being intimidated by the constant flow of vehicles. During the initial encounter, several photographs of the vulture were taken. A few hours later, around 8:29 a.m., the same vulture was observed again on the ground near the empty shell of a mollusk of the genus \u003cem\u003eMegalobulimus\u003c/em\u003e, which was pink in color. The vulture moved towards the shell, a behavior initially interpreted as a search for food remains. However, an unusual behavior was observed, in which the vulture appeared to treat the shell as an egg, displaying signs of nesting (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). During the observation, a local resident reported that the bird had been present in the area for at least a week and was fending off dogs that tried to approach. About a month after the event, a team member returned to the site and found that the vulture was still there, although they did not have a camera to document new images. Two days later, upon returning with photographic equipment, the vulture was no longer present.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eAmong the hypotheses presented, it was not possible to fully fit the vulture's behavior into any one of them, as we could not determine the shell's history before being used by the bird. Furthermore, it is crucial to gather more records similar to the one described, as only by fully monitoring the individual\u0026rsquo;s routine and interaction with the pseudo-egg can we understand the origin and primary reason for this behavior. As a result, we were able to document a previously unreported behavior for the species, \u003cem\u003eCoragyps atratus\u003c/em\u003e, thus expanding the current knowledge about its behavioral repertoire and ecological interactions. This novel observation highlights the importance of detailed field studies in unveiling unexpected aspects of species' life histories.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe vulture's stay in the area for just over a month coincides with the species\u0026rsquo; incubation period, further suggesting the bird's attempt to incubate the pseudo-egg, along with its aggressive behavior towards potential predators. It is important to highlight the account of Murphy, a 31-year-old bald eagle (\u003cem\u003eHaliaeetus leucocephalus\u003c/em\u003e), observed caring for a rock as if it were an egg at the World Bird Sanctuary in Missouri (RFS website). This behavior is the most similar to the observed vulture behavior found in the literature. Moreover, it is worth noting that the behavior of many animals in captivity may differ significantly from what is seen in their natural habitat, due to factors such as the absence of environmental stimuli, social interactions, and hunting opportunities (Morgan and Tromborg, 2007).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThus, we contribute here the first documented record of pseudo-egg incubation by vultures. This report opens up avenues for new studies investigating bird species and the factors leading to the incubation of inanimate objects as eggs. Lastly, we emphasize the importance of birdwatching practices by the public and the deposit of these records in citizen science platforms, allowing researchers to make new discoveries and conduct further studies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI am deeply grateful to my birdwatching groups, \u0026apos;Caatingueiros\u0026apos; and \u0026apos;Jaquinhas de Garga\u0026uacute;,\u0026apos; as it was during a field trip with members of these groups that I had the opportunity to witness the unusual behavior of a vulture incubating a shell. I would also like to express my gratitude to my friends Jo\u0026atilde;o Pedro and Thiago Zanetti, who accepted the invitation to co-author this scientific note with me. Thank you all very much.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe can confirm that the authors have no conflicts of interest to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBaerends, G. P., Drent, R. H., Glas, P. \u0026amp; Groenewold, H. 1970. An ethological analysis of incubation behaviour in the Herring Gull. Behaviour 17(Suppl.): 135\u0026ndash;235.\u003c/li\u003e\n \u003cli\u003eBaidoo, K. 2024. Agonistic Interactions and Tail-cocking Posture in the Black Vulture (\u003cem\u003eCoragyps atratus\u003c/em\u003e). (Senior thesis). Princeton University.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eBartholomew, G.A. \u0026amp; Howell,T. R. 1964. Experiments on nesting behaviour of Laysan and Black-footed albatrosses. Animal Behaviour 12: 549\u0026ndash;558.\u003c/li\u003e\n \u003cli\u003eBeer, C. G. (1961). Incubation and nest building behaviour of Black-headed Gulls. 1: Incubation behaviour in the incubation period. Behaviour 18: 62\u0026ndash;105.\u003c/li\u003e\n \u003cli\u003eBeer, C. G. 1965. Clutch size and incubation behaviour in Black-billed Gulls (Larus bulleri). Auk 82: 1\u0026ndash;18.\u003c/li\u003e\n \u003cli\u003eColeman, J. S., \u0026amp; Fraser, J. D. (1987). Food habits of Black and Turkey vultures in Pennsylvania and Maryland. \u003cem\u003eThe Journal of wildlife management\u003c/em\u003e, 733-739.\u003c/li\u003e\n \u003cli\u003eConover, M.R. (1985) Foreign Objects In Bird Nests. Auk 102 (4):696\u0026ndash;700\u003c/li\u003e\n \u003cli\u003eCoulter, M.C. (1980) \u0026quot;Stones: an Important Incubation Stimulus for Gulls and Terns,\u0026quot; The Auk: Vol. 97: Iss. 4, Article 39.\u003c/li\u003e\n \u003cli\u003eGrant, G. S., Pettit,T. D., Rahn, H.,Whittow, G. C. \u0026amp; Paganelli, C.V. 1982.Water loss from Laysan and Black-footed albatross eggs. Physiological Zoology 55: 405\u0026ndash;414.\u003c/li\u003e\n \u003cli\u003eLanglois, L.A., Murb\u0026ouml;ck, K., Bulla, M., Kempenaers, B. (2012) Unusual incubation: Long-billed Dowitcher incubates mammalian bones. Ardea 100:206\u0026ndash;210. https://doi.org/10.5253/078.100.0213\u003c/li\u003e\n \u003cli\u003eLee, D.L. (1998) 3542. The journal of the Elisha Mitchell Scientific Society 114 (3):163\u003c/li\u003e\n \u003cli\u003eMellink, E. (2002). Pseudo-eggs of brown Sula leucogaster and blue-footed S. nebouxii boobies in the Gulf of California, Mexico. Marine Ornithology, 30, 43-44.\u003c/li\u003e\n \u003cli\u003eMonsalvo, J. A., Silva, M. A., Heming, N. M., \u0026amp; Marini, M. \u0026Acirc;. (2020). Geographical variation and current knowledge on breeding traits of vultures in the neotropics. Ornithology Research, 28(1), 13-37.\u003c/li\u003e\n \u003cli\u003eMorgan, K. N., \u0026amp; Tromborg, C. T. (2007). Sources of stress in captivity. Applied animal behaviour science, 102(3-4), 262-302.\u003c/li\u003e\n \u003cli\u003eNisbet, I. 1997. Female Common Terns Sterna hirundo eating mollusc shells: evidence for calcium deficits during egg laying. Ibis 139: 400\u0026ndash;401.\u003c/li\u003e\n \u003cli\u003eParker, P. G., Waite, T. A., \u0026amp; Decker, M. D. (1995). Kinship and association in communally roosting black vultures. Animal Behaviour, \u003cem\u003e49\u003c/em\u003e(2), 395-401.\u003c/li\u003e\n \u003cli\u003ePower, A., Newton, S., O\u0026rsquo;connor, I. (2018) Common Terns Sterna hirundo incubating Common Garden Snail shells Helix aspersa on Rockabill Island. Seabird 31:88\u0026ndash;91\u003c/li\u003e\n \u003cli\u003eRabenold, P. P. (1986). Family associations in communally roosting black vultures. The Auk, 103(1), 32-41.\u003c/li\u003e\n \u003cli\u003eRush, S. A., \u0026amp; Naveda-Rodr\u0026iacute;guez, A. (2024). Conspecific nest destruction by black vulture (\u003cem\u003eCoragyps atratus\u003c/em\u003e). \u003cem\u003eOrnithology Research\u003c/em\u003e, \u003cem\u003e32\u003c/em\u003e(1), 40-43.\u003c/li\u003e\n \u003cli\u003eSchoombie, S. \u0026amp; Schoombie, J. (2017) Pseudo-egg \u0026ldquo;fabrication\u0026rdquo; by Grey-headed Albatrosses Thalassarche chrysostoma on Marion Island. SEABIRD 30:71\u0026ndash;74\u003c/li\u003e\n \u003cli\u003eSugden, J.W. (1947) Exotic Eggs In Nests Of California Gulls. Condor 49:93\u0026ndash;96\u003c/li\u003e\n \u003cli\u003eTwomey, A.C. (1948) The Condor. 5-6. California Gulls And Exotic Eggs. Condor 50 (3):97\u0026ndash;100\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ornithology-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"orni","sideBox":"Learn more about [Ornithology Research](https://link.springer.com/journal/43388)","snPcode":"43388","submissionUrl":"https://submission.nature.com/new-submission/43388/3","title":"Ornithology Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Nesting behavior, Inanimate objects, Incubation period, Behavioral interaction, Bird-pseudo-egg interactions","lastPublishedDoi":"10.21203/rs.3.rs-6522153/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6522153/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInanimate objects, known as pseudo-eggs, have been observed in the nests of various bird species, often being incubated as if they were real eggs. This study presents the first documented case of pseudo-egg incubation by \u003cem\u003eCoragyps atratus\u003c/em\u003e, observed in the semi-arid region of Paraíba, Brazil, where an individual treated a mollusk shell as an egg, displaying nesting behavior and aggression toward potential predators. The vulture's presence at the site for over a month coincided with the species' average incubation period, suggesting a significant behavioral interaction with the object. This report expands knowledge on bird-pseudo-egg interactions and underscores the need for further studies to understand the underlying factors driving such behaviors.\u003c/p\u003e","manuscriptTitle":"First Documented Case of Pseudo-egg Incubation by Coragyps atratus in a Semiarid Environments","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-08 06:17:50","doi":"10.21203/rs.3.rs-6522153/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-14T19:05:06+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-11T20:07:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-04T15:18:53+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-15T14:07:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"56673618659356220755945761160215197441","date":"2025-07-14T22:35:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"50697276935169779953907715345653056283","date":"2025-07-10T20:27:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"160391657374442304952310441226804648581","date":"2025-07-04T07:16:45+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-03T11:49:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-08T09:00:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-08T08:50:51+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ornithology Research","date":"2025-04-24T15:20:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ornithology-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"orni","sideBox":"Learn more about [Ornithology Research](https://link.springer.com/journal/43388)","snPcode":"43388","submissionUrl":"https://submission.nature.com/new-submission/43388/3","title":"Ornithology Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ea263165-32a2-412c-95d1-e82133f1f4c3","owner":[],"postedDate":"July 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-03-08T01:08:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-08 06:17:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6522153","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6522153","identity":"rs-6522153","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}