Developmental stage-dependent effects of perceived predation risk on physiology and fledging success of tree swallows (Tachycineta bicolor)

Abstract

The risk of predation directly affects physiology, behavior, and fitness of wild birds. Social interactions with conspecifics may affect how individuals respond to stressors such as predators. Strong social connections could help individuals recover from a stressful experience; 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. Here, 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 negatively affected their nestlings condition, telomere lengths, and fledging success. However, the effects of experimental manipulations were timing-dependent: simulated predation during the early nestling period was more detrimental than predation during incubation. 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 affect nestling size, indicating an effect of the social environment on reproductive success. Our data demonstrate that transient stressors on breeding female birds can have carry-over effects on their nestlings, some of which may be long-lasting.

Joint effects of social interactions and environmental challenges on physiology, internal microbiome, and reproductive performance in tree swallows (Tachycineta bicolor)

“…Thermal environment during development is known to be important for tree swallows (Shipley et al, 2020, 2022; Uehling et al, 2020) and could have resulted in different overall energy expenditures for nestlings in predator-treated nests if nestlings were more exposed to ambient temperature because of reduced parental brooding. While some studies have suggested that nestlings might directly respond to predator cues (Ibáñez-Álamo et al, 2011; Zwaan & Martin, 2020), there was no evidence for these effects in our study (McNew et al, 2022).…”

“…Thus, it is unclear exactly why fewer nestlings fledged from predator-treated nests, though it seems likely that mortality soon after hatching played a role. We only found a clear effect of predator treatments on fledging success when the treatments occurred during the nestling period, suggesting that the effect was sensitive to timing in the breeding cycle (see McNew et al, 2022 for further discussion). Although it is worth noting that even in experiment two, nests that received the predation treatment only fledged an average of 60% of the nestlings as control nests, but given the variation and sample size this difference was not statistically distinguishable.…”

“…We assessed the support for either interactions between the treatments or main effects of each treatment by comparing marginal effects using the package where appropriate (Lenth, 2020). Note that more detailed analyses of the effect of treatments and cross fostering on nestling development and physiology are included in separate studies (McNew et al, 2022; Taff, Johnson, et al, 2022).…”

“…However, we also collected similar data and carried out an equal brood size cross fostering experiment on nestlings during these years. Primary analyses of nestling data are presented in a separate study (McNew et al, 2022). On day 12 after hatching, we banded nestlings with a USGS aluminum band, took the same morphological measurements as described above for adults, and took blood samples.…”

Social signal manipulation and environmental challenges have independent effects on physiology, internal microbiome, and reproductive performance in tree swallows (Tachycineta bicolor)

“…However, we also collected similar data and carried out an equal brood size cross-fostering experiment on nestlings during these years; each nest included in this study had an equal number of nestlings cross-fostered with another nest of the same age. Primary analyses of nestling data are presented in a separate study (McNew et al, 2022). On Day 12 after hatching, we banded nestlings with a United States Geological Survey aluminum band, took the same morphological measurements as described above for adults, and took blood samples.…”