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Abstract The risk of predation directly affects the physiology, behavior, and fitness of wild birds. Strong social connections with conspecifics could help individuals recover from a stressful experience such as a predation event; however, competitive interactions also have the potential to exacerbate stress. Few studies have investigated the interaction between environmental stressors and the social landscape in wild bird populations. In 2 years of field studies, we experimentally simulated predation attempts on breeding female tree swallows (Tachicyneta bicolor). At the same time, we manipulated female breast plumage color, a key social signal. Simulated predation events on tree swallows early in the nestling period reduced young nestlings' mass by approximately 20% and shortened telomere lengths. Ultimately, only 31% of nestlings in the predation group fledged compared with 70% of control nestlings. However, the effects of experimental manipulations were timing dependent: the following year when we swapped the order of the experimental manipulations and simulated predation during incubation, there were no significant effects of predation on nestling condition or fledging success. Contrary to our expectations, manipulation of the social environment did not affect the response of tree swallows to simulated predation. However, manipulating female plumage during the nestling period did reduce nestling skeletal size and mass, although the effects depended on original plumage brightness. Our data demonstrate that transient stressors on female birds can have carry‐over effects on their nestlings if they occur during critical periods in the breeding season.
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Nestling growth rate and food consumption increases under experimentally prolonged daylength in a New World sparrow
When evaluating avian reproduction, life history theory examines the trade‐offs between parental effort, the number and size of offspring, and the rate of nestling development. The growth rates and body sizes of developing birds vary geographically and can diverge with both latitude and migratory strategy. In terms of offspring size, growth rate can deviate in nestlings of the same or similar species due to the correlated influences of weather events, predation pressure, food availability, number of nestmates and parental provisioning. Furthermore, a longer photoperiod for species nesting at higher latitudes increases the duration over which a nestling can be fed each day, and increased nestling provisioning has been positively correlated with growth rate. Whether the amount of time a bird is fed during development drives this variation in growth rate and morphology is unknown. By removing supplemental environmental stressors (e.g. weather, predation) and standardizing feeding rate and environment, we explored the influence of daily duration of nestling provisioning on dark‐eyed junco Junco hyemalis nestlings. We hand‐reared 65 chicks of a sedentary junco subspecies J. h. carolinensis under both their natural photoperiod and the longer photoperiod of a closely related migratory subspecies J. h. hyemalis and compared growth rate, mass, morphology and the amount of food consumed. Average growth rate, fasted mass, wing length and total daily food consumption were all greater in birds hand‐reared under the longer, more northern photoperiod treatment. These findings suggest that increased daily photoperiod at higher latitudes may allow for greater total food provisioning and thus may play a role in the ability of parents in compressed breeding seasons to produce high quality offspring. This points to a trade‐off between provisioning effort and nestling growth rate in lower latitude (shorter photoperiod) populations and points to an important role of developmental plasticity on growth rate and morphology.
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- PAR ID:
- 10466173
- Date Published:
- Journal Name:
- Journal of Avian Biology
- ISSN:
- 0908-8857
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The dark-eyed junco (Junco hyemalis) has experienced rapid phenotypic diversification within the last 18,000 years, resulting in several subspecies that reside in partially overlapping regions across North America. These subspecies have distinct plumage and morphology. If members of a subspecies disproportionately mate with one another, we would expect genetic differences to accumulate between the subspecies. In parallel, their learned songs could also accumulate changes. If song is used by individuals to recognize members of their own subspecies during mate selection, which would prevent the production of less fit hybrid offspring between subspecies, then song differences might co-localize with subspecies boundaries. Here, we quantify 10 song features to explore subspecies-level song variation using song recordings from community-science databases. We build a machine learning classifier to measure how accurately the subspecies’ songs can be distinguished from one another. Here, we show that songs of dark-eyed junco subspecies exhibit significant song-feature differences. However, these differences do not necessarily lead to distinguishability between subspecies. Notably, we find that subspecies pairs with adjacent ranges that do not hybridize have much more distinguishable songs, and also more evidence for genetic differentiation, than pairs that are known to hybridize. Thus, song distinguishability appears to have predictive power about which subspecies will hybridize, suggesting that song might play a role in reinforcing certain subspecies boundaries more than others. Finally, we analyze subspecies-level song differences alongside available genetic data and geographic coordinates to characterize the current evolutionary landscape of the dark-eyed junco subspecies complex. We observe geographic signal in the song and genetic data, indicating that individuals who share a range are more likely to share song characteristics and be genetically similar. This study illuminates the existence of subspecies-level song differences in the dark-eyed junco and provides further clarity on the role learned song plays in reinforcing reproductive boundaries between dark-eyed junco subspecies.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/jav.03113
