This paper advances an hypothesis that the primary adaptive driver of seasonal migration is maintenance of site fidelity to familiar breeding locations. We argue that seasonal migration is therefore principally an adaptation for geographic persistence when confronted with seasonality -analogous to hibernation, freeze tolerance, or other organismal adaptations to cyclically fluctuating environments. These ideas stand in contrast to traditional views that bird migration evolved as an adaptive dispersal strategy for exploiting new breeding areas and avoiding competitors. Our synthesis is supported by a large body of research on avian breeding biology that demonstrates the reproductive benefits of breeding-site fidelity. Conceptualizing migration as an adaptation for persistence places new emphasis on understanding the evolutionary trade-offs between migratory behaviour and other adaptations to fluctuating environments both within and across species. Seasonality-induced departures from breeding areas, coupled with the reproductive benefits of maintaining breeding-site fidelity, also provide a mechanism for explaining the evolution of migration that is agnostic to the geographic origin of migratory lineages (i.e. temperate or tropical). Thus, our framework reconciles much of the conflict in previous research on the historical biogeography of migratory species. Although migratory behaviour and geographic range change fluidly and rapidly in many populations, we argue that the loss of plasticity for migration via canalization is an overlooked aspect of the evolutionary dynamics of migration and helps explain the idiosyncratic distributions and migratory routes of long-distance migrants. Our synthesis, which revolves around the insight that migratory organisms travel long distances simply to stay in the same place, provides a necessary evolutionary context for understanding historical biogeographic patterns in migratory lineages as well as the ecological dynamics of migratory connectivity between breeding and non-breeding locations.

the degree to which species can rapidly adapt is key to survival in the face of climatic and other anthropogenic changes. for little brown bats (Myotis lucifugus), whose populations have experienced declines of over 90% because of the introduced fungal pathogen that causes white-nose syndrome (WnS), survival of the species may ultimately depend upon its capacity for adaptive change. Here, we present evidence of selectively driven change (adaptation), despite dramatic nonadaptive genomic shifts (genetic drift) associated with population declines. We compared the genetic makeups of wild survivors versus non-survivors of WNS, and found significant shifts in allele frequencies of genes associated with regulating arousal from hibernation (GABARB1), breakdown of fats (cGMP-PK1), and vocalizations (FOXP2). Changes at these genes are suggestive of evolutionary adaptation, given that WNS causes bats to arouse with unusual frequency from hibernation, contributing to premature depletion of fat reserves. However, whether these putatively adaptive shifts in allele frequencies translate into sufficient increases in survival for the species to rebound in the face of WNS is unknown. Events that kill large portions of populations, including naturally and anthropogenically induced disasters, increasingly threaten biodiversity 1,2. Invasive species are a major trigger of these declines 3 , including invasive pathogens, against which native species can experience high mortality due to a lack of co-evolutionary defenses 4-6. Introduced fungal pathogens can be particularly dangerous-they can frequently survive in the environment for extended periods, affect a relatively broad range of hosts, and can be highly virulent 7 , thereby driving mass-mortalities of native species (e.g. amphibian chytrid 8 , snake fungal disease 9 , sea fan aspergillosis 10 , and others 11-13) as well as threatening agricultural crops 14,15 (e.g. rice blast disease 16 and Fusarium wilt in bananas 17). Although host mortalities may have little impact on fungal pathogens, the pathogens can exert incredibly strong selective pressures on their host populations 18. A pressing conservation question is whether host populations can evolve resistance or tolerance during such epidemics-a necessary first step towards preventing extinction. Strong selective pressures might theoretically lead to an evolutionary rescue effect if host populations adapt 19. However, acute events that kill off most members of a species also reduce the genetic diversity upon which natural selection can act, thereby limiting the capacity for adaptive change 20. White-nose syndrome (WNS) is a disease affecting bats, which is caused by the invasive fungus Pseudogymnoascus destructans 21. This highly destructive pathogen has decimated populations of bats, with 12 North American species currently affected 22 , and some populations experiencing losses of 90-100% 23. The fungus was first inadvertently introduced to North America by humans in 2006 (in the northeastern U.S.) 24 , and is spreading across...

White-nose syndrome is an introduced fungal disease that has reduced the size of hibernating populations of little brown bats ( Myotis lucifugus ) by 90% across much of eastern North America since 2007.  Herein, we report the recapture of eight, banded, male little brown bats with minimum ages of 18.6–25.6 years.  The recaptures occurred during winter 2019–2020, at a hibernaculum in Michigan where white-nose syndrome likely has been present since 2013–2014, indicating that these old and apparently healthy males are in their seventh season of exposure to the disease.  Hence, our data suggest that a long life in little brown bats and existence of white-nose syndrome are not necessarily incompatible.

Freezing temperatures are inherently challenging for life, which is water based. How species cope with these conditions fundamentally shapes ecological and evolutionary processes. Despite this, there is no comprehensive conceptual framework for cold-survival strategies—seasonal migration, cold resistance and torpor. Here, I propose a framework with four components for conceptualizing and quantifying cold-survival strategies. Cold-survival strategies are (i) collectively encompassed by the proposed framework, and that this full breadth of strategies should be considered in focal species or systems ( comprehensive consideration ). These strategies also (ii) exist on a spectrum, such that species can exhibit partial use of strategies, (iii) are non-exclusive, such that some species use multiple strategies concurrently ( combined use ) and (iv) should collectively vary inversely and proportionally with one another when controlling for the external environment (e.g. when considering species that occur in sympatry in their summer range), such that use of one strategy reduces, collectively, the use of others ( proportional use ). This framework is relevant to understanding fundamental patterns and processes in evolution, ecology, physiology and conservation biology.

We examine factors affecting the winter range limit of a migrating mammal, the silver-haired bat (Lasionycteris noctivagans), in states surrounding Lake Michigan, the fourth largest freshwater lake in the world. Using 555 citizen-based captures gathered between 1977 and 2016, we show that silver-haired bats overwinter (December-February) as far north as the 45th parallel, in areas roughly demarcated by the −12.2 • C (10 • F) mean daily minimum isotherm for January. Although summering populations adjacent to the lake are dominated by males, wintering animals are predominantly female and presumably migrants from north of Lake Superior. Logistic regression suggests that silver-haired bats are more likely to overwinter in warm areas, in counties near the lake, in urbanized locales, and on the west side of the lake. We believe that these small-bodied, solitary bats are hibernating in buildings and that use of human-made structures has allowed the silver-haired bat to overwinter in regions that are devoid of mines, caves and rock crevices and that are too cold for successful hibernation in trees. Lake Michigan impacts where this animal overwinters, presumably through the moderating influence of the lake on multiple aspects of the surrounding climate and because the shoreline likely is a major migratory pathway.