Hatching failure in an aerial insectivore, the tree swallow (Tachycineta bicolor), is driven by embryonic mortality, not infertility

Hatching failure in an aerial insectivore, the tree swallow (Tachycineta bicolor), is driven by embryonic mortality, not infertility | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 17 February 2026 V1 Latest version Share on Hatching failure in an aerial insectivore, the tree swallow (Tachycineta bicolor), is driven by embryonic mortality, not infertility Authors : Hannah Tench 0009-0003-3951-5140 [email protected] , Nicola Hemmings 0000-0003-2418-3625 , and Russell Dawson Authors Info & Affiliations https://doi.org/10.22541/au.177128834.49461026/v1 181 views 97 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Aerial insectivores in North America have rapidly declined over the past half century, and factors contributing to these declines are poorly understood. To understand demographic changes in populations, it is important to investigate mortality in all life stages, including prenatally. Egg development is a crucial stage in the life cycle of birds, and across species including aerial insectivores, up to 17% of eggs fail to hatch under normal conditions. Hatching failure is due to either infertility or embryonic mortality; however, methods to distinguish between these two causes have been underused. In 2022 and 2023, we monitored 1090 eggs laid by tree swallows (Tachycineta bicolor) from 191 nests at three study sites in British Columbia, Canada. Using fluorescence microscopy to identify embryonic and sperm nuclei, we conservatively estimated that 98.3% – 100% of eggs were fertile, and most cases of hatching failure were therefore due to embryonic mortality, not infertility. Embryonic mortality was most likely to occur during early incubation, before development is usually macroscopically visible. We also used fluorescence microscopy to examine 114 eggs laid by tree swallows kept in long-term frozen storage and found that not only could fertility be assessed, but the fertility rate of these eggs was similarly close to 100%. To our knowledge, this study is the first to quantify fertility using embryonic nuclei in tree swallows, and provides the basis for further investigation into factors contributing to hatching failure in this species. Our success using frozen eggs for fertility testing is especially relevant for conservation groups and captive breeding facilities that may already have unhatched eggs stored in freezers, or are limited by capacity or funding and need to place eggs in long-term storage until resources are available for testing. Supplementary Material File (main text_hatching failure in tree swallows.docx) Download 721.82 KB Information & Authors Information Version history V1 Version 1 17 February 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords aerial insectivores fertility fluorescence microscopy hatching success tree swallows Authors Affiliations Hannah Tench 0009-0003-3951-5140 [email protected] University of Northern British Columbia View all articles by this author Nicola Hemmings 0000-0003-2418-3625 University of Sheffield View all articles by this author Russell Dawson University of Northern British Columbia View all articles by this author Metrics & Citations Metrics Article Usage 181 views 97 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Hannah Tench, Nicola Hemmings, Russell Dawson. Hatching failure in an aerial insectivore, the tree swallow (Tachycineta bicolor), is driven by embryonic mortality, not infertility. Authorea . 17 February 2026. DOI: https://doi.org/10.22541/au.177128834.49461026/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . Format Please select one from the list RIS (ProCite, Reference Manager) EndNote BibTex Medlars RefWorks Direct import Tips for downloading citations document.getElementById('citMgrHelpLink').addEventListener('click', function() { popupHelp(this.href); return false; }); $(".js__slcInclude").on("change", function(e){ if ($(this).val() == 'refworks') $('#direct').prop("checked", false); $('#direct').prop("disabled", ($(this).val() == 'refworks')); }); View Options View options PDF View PDF Figures Tables Media Share Share Share article link Copy Link Copied! Copying failed. 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