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1. A pre‐breeding immune challenge delays reproduction in the female dark‐eyed junco Junco hyemalis

   https://doi.org/10.1111/jav.01464  

   Needham, Katie B. ; Cook, Natalie J. ; Rutherford, Alexa R. ; Greives, Timothy J. ( September 2017 , Journal of Avian Biology)

   Precise timing of life‐history transitions in predictably changing environments is hypothesized to aid in individual survival and reproductive success, by appropriately matching an animal's physiology and behavior with prevailing environmental conditions. Therefore, it is imperative for individuals to time energetically costly life‐history stages (i.e. reproduction) so they overlap with seasonal peaks in food abundance and quality. Female lifetime reproductive fitness is affected by several factors that influence energy balance, including arrival date, timing of egg production, and energetic condition. Therefore, any extra energetic costs during reproduction may negatively affect timing of egg production, and ultimately a female's fitness. For example, mounting an immunological response elicits a high energetic cost, and this transfer of resources towards cell and immune system maintenance could have direct negative effects on reproductive timing. In order to determine whether an immune challenge delays onset of breeding (i.e. egg production), we administered either a humoral immune challenge (keyhole limpet hemocyanin (KLH)) (treatment) or physiological saline (control) to free‐living female dark‐eyed juncosJunco hyemalisin the period immediately prior to egg‐laying (∼4 weeks). We found that KLH‐injected females artificially delayed clutch initiation when compared to control females. These data help to refine our understanding of how free‐living birds allocate resources between reproduction and self‐maintenance processes during the critical pre‐laying period of the annual cycle.

    

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2. Long‐term research and hierarchical models reveal consistent fitness costs of being the last egg in a clutch

   https://doi.org/10.1111/1365-2656.13232  

   Acevedo, Cheyenne R. ; Riecke, Thomas V. ; Leach, Alan G. ; Lohman, Madeleine G. ; Williams, Perry J. ; Sedinger, James S. ; Koons, ed., David ( April 2020 , Journal of Animal Ecology)

   Maintenance of phenotypic heterogeneity in the face of strong selection is an important component of evolutionary ecology, as are the consequences of such heterogeneity. Organisms may experience diminishing returns of increased reproductive allocation as clutch or litter size increases, affecting current and residual reproductive success. Given existing uncertainty regarding trade‐offs between the quantity and quality of offspring, we sought to examine the potential for diminishing returns on increased reproductive allocation in a long‐lived species of goose, with a particular emphasis on the effect of position in the laying sequence on offspring quality.

   To better understand the effects of maternal allocation on offspring survival and growth, we estimated the effects of egg size, timing of breeding, inter‐ and intra‐annual variation, and position in the laying sequence on gosling survival and growth rates of black brantBranta bernicla nigricansbreeding in western Alaska from 1987 to 2007.

   We found that gosling growth rates and survival decreased with position in the laying sequence, regardless of clutch size. Mean egg volume of the clutch a gosling originated from had a positive effect on gosling survival (β = 0.095, 95% CRI: 0.024, 0.165) and gosling growth rates (β = 0.626, 95% CRI: 0.469, 0.738). Gosling survival (β = −0.146, 95% CRI: −0.214, −0.079) and growth rates (β = −1.286, 95% CRI: −1.435, −1.132) were negatively related to hatching date.

   These findings indicate substantial heterogeneity in offspring quality associated with their position in the laying sequence. They also potentially suggest a trade‐off mechanism for females whose total reproductive investment is governed by pre‐breeding state.

    

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3. Birds advancing lay dates with warming springs face greater risk of chick mortality

   https://doi.org/10.1073/pnas.2009864117  

   Shipley, J. Ryan ; Twining, Cornelia W. ; Taff, Conor C. ; Vitousek, Maren N. ; Flack, Andrea ; Winkler, David W. ( September 2020 , Proceedings of the National Academy of Sciences)

   In response to a warming planet with earlier springs, migratory animals are adjusting the timing of essential life stages. Although these adjustments may be essential for keeping pace with resource phenology, they may prove insufficient, as evidenced by population declines in many species. However, even when species can match the tempo of climate change, other consequences may emerge when exposed to novel conditions earlier in the year. Here, using three long-term datasets on bird reproduction, daily insect availability, and weather, we investigated the complex mechanisms affecting reproductive success in an aerial insectivore, the tree swallow (Tachycineta bicolor). By examining breeding records over nearly half a century, we discovered that tree swallows have continuously advanced their egg laying by ∼3 d per decade. However, earlier-hatching offspring are now exposed to inclement weather events twice as often as they were in the 1970s. Our long-term daily insect biomass dataset shows no long-term trends over 25 y but precipitous drops in flying insect numbers on days with low ambient temperatures. Insect availability has a considerable impact on chick survival: Even a single inclement weather event can reduce offspring survival by >50%. Our results highlight the multifaceted threats that climate change poses on migrating species. The decoupling between cold snap occurrence and generally warming spring temperatures can affect reproductive success and threaten long-term persistence of populations. Understanding the exact mechanisms that endanger aerial insectivores is especially timely because this guild is experiencing the steepest and most widespread declines across North America and Europe.

    

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4. Ontogenetic effects of brood parasitism by the Brown‐headed Cowbird on host offspring

   https://doi.org/10.1002/ecy.3925  

   Jones, Todd M. ; Di Giovanni, Alexander J. ; Hauber, Mark E. ; Ward, Michael P. ( January 2023 , Ecology)

   Nest‐sharer avian brood parasites do not evict or otherwise kill host chicks, but instead inflict a range of negative effects on their nestmates that are mediated by interactions between the parasite and host life history traits. Although many of the negative fitness effects of avian brood parasitism are well documented across diverse host species, there remains a paucity of studies that have examined the impacts of parasitism across the entirety of host ontogeny (i.e., from when an egg is laid until independence). More specifically, few studies have examined the impact of brood parasitism on the pre‐ and post‐fledging development, physiology, behavior, and survival of host offspring. To help fill this knowledge gap, we assessed the effects of brood parasitism by Brown‐headed Cowbirds (Molothrus ater) across the ontogeny (incubation, nestling, and post‐fledging period) of nine sympatrically breeding host species in central Illinois, USA; due to sample sizes, impacts on the post‐fledging period were only examined in two of the nine species. Specifically, we examined the impact of brood parasitism on ontogenetic markers including the embryonic heart rate, hatching rate, nestling period length, nest survival, and offspring growth and development. Additionally, in species in which we found negative impacts of cowbird parasitism on host nestmate ontogeny, we examined whether the difference in adult size between parasites and their hosts and their hatching asynchrony positively predicted variation in host costs across these focal taxa. We found that costs of cowbird parasitism were most severe during early nesting stages (reduction in the host clutch or brood size) and were predicted negatively by host size and positively by incubation length. In contrast, we only found limited costs of cowbird parasitism on other stages of host ontogeny; critically, post‐fledging survival did not differ between host offspring that fledged alongside cowbirds and those that did not. Our findings (i) highlight the direct costs of cowbird parasitism on host fitness, (ii) provide evidence for when (the stage) those costs are manifested, and (iii) may help to explain why many anti‐cowbird defenses of hosts have evolved for protection from parasitism during the laying and incubation stages.

    

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5. Convergent niche shifts of endangered parrots (genus Amazona ) during successful establishment in urban southern California

   https://doi.org/10.1111/ddi.13817  

   Ramirez, Brenda R. ; Freeland, Rowdy J. ; Muhlheim, Allison ; Zellmer, Amanda J. ; DeRaad, Devon A. ; Kirsch, Eliza J. ; Mutchler, Marquette J. ; Secor, Maeve B. ; Reckling, Kelsey R. ; Schedl, Margaret E. ; et al ( February 2024 , Diversity and Distributions)

   Introduced species offer insight on whether and how organisms can shift their ecological niches during translocation. The genusAmazonaoffers a clear test case, where sister species Red‐crowned (A. viridigenalis) and Lilac‐crowned Parrots (A. finschi) have established breeding populations in southern California following introduction via the pet trade from Mexico where they do not coexist. After establishment in the 1980s, introduced population sizes have increased, with mixed species flocks found throughout urban Los Angeles. Here, we investigate the differences between the environmental conditions of the native and introduced ranges of these now co‐occurring species.

   Southern California and Mexico.

   Using environmental data on climate and habitat from their native and introduced ranges, we tested whether Red‐crowned and Lilac‐crowned Parrots have divergent realized niches between their native ranges, and whether each species has significantly shifted its realized niche to inhabit urban southern California. We also analysed data from Texas and Florida introductions of Red‐crowned Parrots for comparative analysis.

   There are significant differences in the native‐range niches of both parrot species, but a convergence into a novel, shared environmental niche into urban southern California, characterized by colder temperatures, less tree cover and lower rainfall. Texas and Florida Red‐crowned Parrots also show evidence for niche shifts with varying levels of niche conservatism through the establishment of somewhat different realized niches.

   Despite significant niche shifts, introduced parrots are thriving, suggesting a broad fundamental niche and an ability to exploit urban resources. Unique niche shifts in different U.S. introductions indicate thatAmazonaparrots can adapt to diverse environmental conditions, with cities offering a resource niche and the timing of introduction playing a crucial role. Cities can potentially serve as refugia for threatened parrot species, but the risk of hybridization between species emphasizes the need for ongoing monitoring and genetic investigations.

    

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