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  1. Abstract

    Many animals rely on photoperiodic and non-photoperiodic environmental cues to gather information and appropriately time life-history stages across the annual cycle, such as reproduction, molt, and migration. Here, we experimentally demonstrate that the reproductive physiology, but not migratory behavior, of captive Pine Siskins (Spinus pinus) responds to both food and social cues during the spring migratory-breeding period. Pine Siskins are a nomadic finch with a highly flexible breeding schedule and, in the spring, free-living Pine Siskins can wander large geographic areas and opportunistically breed. To understand the importance of non-photoperiodic cues to the migratory-breeding transition, we maintained individually housed birds on either a standard or enriched diet in the presence of group-housed heterospecifics or conspecifics experiencing either the standard or enriched diet type. We measured body condition and reproductive development of all Pine Siskins and, among individually housed Pine Siskins, quantified nocturnal migratory restlessness. In group-housed birds, the enriched diet caused increases in body condition and, among females, promoted reproductive development. Among individually housed birds, female reproductive development differed between treatment groups, whereas male reproductive development did not. Specifically, individually housed females showed greater reproductive development when presented with conspecifics compared to heterospecifics. The highest rate of female reproductive development, however, was observed among individually housed females provided the enriched diet and maintained with group-housed conspecifics on an enriched diet. Changes in nocturnal migratory restlessness did not vary by treatment group or sex. By manipulating both the physical and social environment, this study demonstrates how multiple environmental cues can affect the timing of transitions between life-history stages with differential responses between sexes and between migratory and reproductive systems.

     
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  2. Our understanding of state-dependent behaviour is reliant on identifying physiological indicators of condition. Telomeres are of growing interest for understanding behaviour as they capture differences in biological state and residual lifespan. To understand the significance of variable telomere lengths for behaviour and test two hypotheses describing the relationship between telomeres and behaviour (i.e. the causation and the selective adoption hypotheses), we assessed if telomere lengths are longitudinally repeatable traits related to spring migratory behaviour in captive pine siskins ( Spinus pinus ). Pine siskins are nomadic songbirds that exhibit highly flexible, facultative migrations, including a period of spring nomadism. Captive individuals exhibit extensive variation in spring migratory restlessness and are an excellent system for mechanistic studies of migratory behaviour. Telomere lengths were found to be significantly repeatable ( R = 0.51) over four months, and shorter pre-migratory telomeres were associated with earlier and more intense expression of spring nocturnal migratory restlessness. Telomere dynamics did not vary with migratory behaviour. Our results describe the relationship between telomere length and migratory behaviour and provide support for the selective adoption hypothesis. More broadly, we provide a novel perspective on the significance of variable telomere lengths for animal behaviour and the timing of annual cycle events. 
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    Physiological preparations for migration generally reflect migratory strategy. Migrant birds fuel long-distance flight primarily with lipids, but carrying excess fuel is costly; thus, the amount of fat deposited prior to departure often reflects the anticipated flight duration or distance between refueling bouts. Seasonal pre-migratory deposition of fat is well documented in regular seasonal migrants, but is less described for more facultative species. We analyze fat deposits of free-living birds across several taxa of facultative migrants in the songbird subfamily Carduelinae, including house finches ( Haemorhous mexicanus ), American goldfinches ( Spinus tristis ), pine siskins ( Spinus pinus ) and four different North American ecotypes of red crossbills ( Loxia curvirostra ), to evaluate seasonal fat deposition during facultative migratory periods. Our data suggest that the extent of seasonal fat deposits corresponds with migratory tendency in these facultative taxa. Specifically, nomadic red crossbills with a seasonally predictable annual movement demonstrated relatively large seasonal fat deposits coincident with the migratory periods. In contrast, pine siskins, thought to be more variable in timing and initiation of nomadic movements, had smaller peaks in fat deposits during the migratory season, and the partial migrant American goldfinch and the resident house finch showed no peaks coincident with migratory periods. Within the red crossbills, those ecotypes that are closely associated with pine habitats showed larger peaks in fat deposits coincident with autumn migratory periods and had higher wing loading, whereas those ecotypes associated with spruces, Douglas-fir and hemlocks showed larger peaks coincident with spring migratory periods and lower wing loading. We conclude that population averages of fat deposits do reflect facultative migration strategies in these species, as well as the winter thermogenic challenges at the study locations. A difference in seasonal fattening and wing loading among red crossbill ecotypes is consistent with the possibility that they differ in their migratory biology, and we discuss these differences in light of crossbill reproductive schedules and phenologies of different conifer species. 
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  5. Abstract

    Building on the predictions of state‐dependent life‐history theory, telomeres are hypothesized to either correlate with or function as an adaptive, proximate mediator of an individual's behaviour and life‐history strategy. To further understand the relationship between telomeres, behaviour and life‐history strategies, we measured male behaviour, telomere lengths and telomere dynamics in a free‐living population of known‐age, male wire‐tailed manakinsPipra filicauda.

    Male wire‐tailed manakins perform coordinated displays with other males at leks and these displays form the basis of long‐term coalition partnerships. Males exhibit consistent individual differences in the number of social partners within their social network and the frequency of social interactions. Male sociality is also positively correlated with both social rise and reproductive success.

    We measured male behaviour using a telemetry‐based, proximity datalogging system and blood telomere lengths were quantified using qPCR. We examined the relationships between telomere length, telomere dynamics, social status, and male behaviour. We also quantified the repeatability of telomere lengths, examined age‐related changes in telomere length, and tested for instances of telomere elongation that exceed residual error in telomere length.

    Telomere length was found to be highly repeatable. More social males exhibited shorter telomeres and higher rates of telomere attrition. Telomeres did not significantly vary with age within or between individuals in either of the male social classes. Two out of 25 individuals exhibited patterns telomere elongation that exceeded residual error in telomere measurements.

    Here we show that telomeres consistently vary between male wire‐tailed manakins and these differences are related to variation in male social behaviour. In this relatively long‐lived species, telomeres appear to be flexible traits that can increase or decrease in length. Overall, this study provides observational support for the hypothesis that telomeres act as a molecular marker that relates to behaviour in a state‐dependent manner. We also provide insight into the molecular consequences of individual variation in male social behaviour.

    A freePlain Language Summarycan be found within the Supporting Information of this article.

     
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