Where do winter crows go? Characterizing partial migration of American Crows with satellite telemetry, stable isotopes, and molecular markers

Townsend, Andrea K.; Frett, Blaire; McGarvey, Anne; Taff, Conor C.

doi:10.1642/auk-18-23.1

Cited by 18 publications

(14 citation statements)

References 57 publications

(83 reference statements)

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“…We also determined that strategy was not fixed: 5 of the 23 birds captured in multiple years changed strategies between winters. While studies of some partially migratory systems have found strategy switching to be uncommon (Gillis et al , Townsend et al ), our results are consistent with the larger number of studies that have found individual strategies are flexible (Able and Belthoff , Ogonowski and Conway , Palacín et al , Hegemann et al ). The occurrence of strategy switching in western bluebirds suggests that migratory strategy is not controlled by a simple genetic dimorphism in this system.…”

Section: Discussionsupporting

confidence: 90%

“…Chan () found that some birds only developed migratory restlessness in the presence of others, an observation which led him to suggest interactions with other individuals may be a key cue for initiating migration in this species (Chan and Kikkawa , Chan ). Social influences have been proposed to play a role in determining migratory strategies in other species, such as great bustards Otis tarda (Palacín et al ), and pied avocets Recurvirostra avosetta (Chambon et al ), where strategies appear to be influenced by an individual's integration into winter flocks.…”

Section: Introductionmentioning

confidence: 99%

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Correlates of alternative migratory strategies in western bluebirds

Dale

Nocera

Franks

et al. 2019

Journal of Avian Biology

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Partial migration occurs when only some animals in a population migrate. While evidence suggests that migratory strategies are partially controlled by genes, individual and environmental conditions which alter the cost‐benefit trade‐off of migration among individuals are also likely to play a role. Three hypotheses have been advanced to explain condition‐dependent partial migration: the arrival time, dominance and body size hypotheses. In this study, we asked whether these hypotheses explained differences in migratory strategy among individuals in a partially migratory population of western bluebirds Sialia mexicana breeding in southern British Columbia, Canada. We used stable hydrogen isotope signatures in claw tissue to determine migratory strategy of individual bluebirds, and examined patterns of migration at both individual and population levels. The proportion of resident bluebirds varied significantly over the three years of the study, and across study sites. Several migrants switched to the resident strategy between years; however, we found no evidence of strategy switching in the opposite direction. Young birds were significantly more likely to be resident than older birds, a pattern which could arise if early arrival is particularly important for birds obtaining a territory for the first time. Furthermore, young females were the most likely of all sex–age classes to be resident, which may reflect a survival advantage of residency for young females. Finally, birds mated assortatively by migratory strategy and isotopic evidence suggests that members of a pair often wintered in the same place. Our results provided no support for the dominance or body size hypotheses, and only limited support for the arrival time hypothesis in bluebirds. However, taken together, we suggest that our findings indicate that social factors may influence migratory strategies in this system.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Correlates of alternative migratory strategies in western bluebirds

Dale

Nocera

Franks

et al. 2019

Journal of Avian Biology

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“…The potential costs of migration are high: migratory individuals may encounter unfamiliar environments with novel threats, as well as the energetic costs of movement (Wikelski et al, ), predation risks (Lindström, ; Ydenberg, Butler, Lank, Smith, & Ireland, ) and temporal investment to the detriment of time otherwise invested in breeding fitness (Alerstam et al, ). The biological processes underlying the evolution of migration are little known (Griswold, Taylor, & Norris, ; Townsend, Frett, McGarvey, & Taff, ; Vélez‐Espino, McLaughlin, & Robillard, ), but in order to have evolved, migration must—in sufficient instances—offer a benefit relative to not migrating (‘residency’ hereafter) to either breeding success or survival (Griswold et al, ; Lundberg, ; McKinnon et al, ; Zúñiga et al, ).…”

Section: Introductionmentioning

confidence: 99%

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

Buchan

Gilroy

Catry

et al. 2019

Journal of Animal Ecology

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Partial migration—wherein migratory and non‐migratory individuals exist within the same population—represents a behavioural dimorphism; for it to persist over time, both strategies should yield equal individual fitness. This balance may be maintained through trade‐offs where migrants gain survival benefits by avoiding unfavourable conditions, while residents gain breeding benefits from early access to resources. There has been little overarching quantitative analysis of the evidence for this fitness balance. As migrants—especially long‐distance migrants—may be particularly vulnerable to environmental change, it is possible that recent anthropogenic impacts could drive shifts in fitness balances within these populations. We tested these predictions using a multi‐taxa meta‐analysis. Of 2,939 reviewed studies, 23 contained suitable information for meta‐analysis, yielding 129 effect sizes. Of these, 73% (n = 94) reported higher resident fitness, 22% (n = 28) reported higher migrant fitness, and 5% (n = 7) reported equal fitness. Once weighted for precision, we found balanced fitness benefits across the entire dataset, but a consistently higher fitness of residents over migrants in birds and herpetofauna (the best‐sampled groups). Residency benefits were generally associated with survival, not breeding success, and increased with the number of years of data over which effect sizes were calculated, suggesting deviations from fitness parity are not due to sampling artefacts. A pervasive survival benefit to residency documented in recent literature could indicate that increased exposure to threats associated with anthropogenic change faced by migrating individuals may be shifting the relative fitness balance between strategies.

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“…Here, we included as “potential breeders” all adult birds sampled during the breeding season (June through August) in each of the two study populations within the same 4‐km‐diameter areas from which we sampled nestlings (Figure ; California: n = 258 males, 134 females, and 262 offspring; New York: n = 33 males, 38 females, and 134 offspring). Individuals at this scale interacted with each other in the winter months at communal roosts and local diurnal activity centres, as indicated by satellite telemetry, GPS telemetry and mark–resight data (Taff et al., ; Townsend, Frett, McGarvey, & Taff, A.K. Townsend, unpublished data).…”

Section: Methodsmentioning

confidence: 88%

Apparent inbreeding preference despite inbreeding depression in the American crow

et al. 2019

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Although matings between relatives can have negative effects on offspring fitness, apparent inbreeding preference has been reported in a growing number of systems, including those with documented inbreeding depression. Here, we examined evidence for inbreeding depression and inbreeding preference in two populations (Clinton, New York and Davis, California, USA) of the cooperatively breeding American crow (Corvus brachyrhynchos). We then compared observed inbreeding strategies with theoretical expectations for optimal, adaptive levels of inbreeding, given the inclusive fitness benefits and population-specific magnitude of inbreeding depression. We found that low heterozygosity at a panel of 33 microsatellite markers was associated with low survival probability (fledging success) and low white blood cell counts among offspring in both populations. Despite these costs, our data were more consistent with inbreeding preference than avoidance: the observed heterozygosity among 396 sampled crow offspring was significantly lower than expected if local adults were mating by random chance. This pattern was consistent across a range of spatial scales in both populations. Theoretically adaptive levels of inbreeding, given the magnitude of inbreeding depression, were predicted to be very low in the California population, whereas complete disassociative mating was predicted in the New York population. Sexual conflict might have contributed to the apparent absence of inbreeding avoidance in crows. These data add to an increasing number of examples of an "inbreeding paradox," where inbreeding appears to be preferred despite inbreeding depression. This article is protected by copyright. All rights reserved.

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Where do winter crows go? Characterizing partial migration of American Crows with satellite telemetry, stable isotopes, and molecular markers

Abstract: BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Cited by 18 publications

References 57 publications

Correlates of alternative migratory strategies in western bluebirds

Correlates of alternative migratory strategies in western bluebirds

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

Apparent inbreeding preference despite inbreeding depression in the American crow

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