Stable mean arrival dates and increasing male variance in spring-migrating American robins

Stable mean arrival dates and increasing male variance in spring-migrating American robins | 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 Search Search ADVANCED SEARCH SCROLL Journal of Avian Biology This is a preprint and has not been peer reviewed. Data may be preliminary. 12 May 2026 V1 Latest version Share on Stable mean arrival dates and increasing male variance in spring-migrating American robins Authors : Richard Thiel [email protected] and Matthew Schuler 0000-0002-4258-3000 [email protected] Authors Info & Affiliations https://doi.org/10.22541/authorea.15003109/v1 Under Review Journal of Avian Biology Peer review timeline 15 views 6 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract American robins (Turdus migratorius) display three plumage phenotypes: males with dark black heads, an intermediate phenotype that is sex-indistinct, and females with gray-brown heads. We investigated potential changes to the predicted protandrous arrival sequence using 1,878 robin observations across 253 sampling days in west-central Wisconsin during the springs of 1983 to 1989 and 2011 to 2019. Males arrived first (mean first-arrival 14 March), intermediate-phenotype birds next (24 March), and females last (30 March). Spring snowstorms occurred in roughly one of every three years and produced no detectable shift in arrival timing, consistent with photoperiod-driven migration patterns. Necropsies of four males killed during an April 2018 snowstorm revealed advanced malnutrition in two individuals, indicating increased stress for males who risk migrating north earlier. Between the early (1983–1989) and late (2011–2019) windows, mean first-arrival dates of all three phenotypes showed no significant changes. However, the year-to-year variance of male arrival date roughly doubled from the early to later window, while female variance remained unchanged. This sex-asymmetric pattern suggests that males absorb climate-driven migration risk through wider arrival flexibility, while females retain a more conservative schedule. Overwintering robins, absent from the study area in the early period, have appeared with increasing regularity since 2003, and the first overwintering female was documented in 2020. As the overwintering population shifts northward and spring weather becomes more variable, late-season storms are likely to disproportionately impact early-arriving males. For now, population-level effects may be buffered by a more conservative female migration strategy. Supplementary Material File (appendix.docx) appendix Download 281.14 KB Information & Authors Information Version history V1 Version 1 12 May 2026 Peer review timeline Under Review Journal of Avian Biology 12 May 2026 Review Complete Collection Journal of Avian Biology Keywords population ecology disease ecology life history Turdus migratorius protandry migration spring snowstorm mortality bet-hedging climate variability eco-immunology maternal effects hormones life-history ageing migration climate change adaptation dispersal bird population ecology disease ecology life history Authors Affiliations Richard Thiel [email protected] Wisconsin Department of Natural Resources, Babcock, United States View all articles by this author Matthew Schuler 0000-0002-4258-3000 [email protected] Wisconsin Department of Natural Resources, Babcock, United States View all articles by this author Metrics & Citations Metrics Article Usage 15 views 6 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Richard Thiel, Matthew Schuler. Stable mean arrival dates and increasing male variance in spring-migrating American robins. Authorea . 12 May 2026. DOI: https://doi.org/10.22541/authorea.15003109/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 . 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