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1. Change in beak overhangs of cliff swallows over 40 years: Partly a response to parasites?

   https://doi.org/10.1371/journal.pone.0263422  

   Wagnon, Gigi S.; Pletcher, Olivia M.; Brown, Charles R. (February 2022, PLOS ONE)

   Ruiz-Rodriguez, Magdalena (Ed.)

   Some birds exhibit a maxillary overhang, in which the tip of the upper beak projects beyond the lower mandible and may curve downward. The overhang is thought to help control ectoparasites on the feathers. Little is known about the extent to which the maxillary overhang varies spatially or temporally within populations of the same species. The colonial cliff swallow ( Petrochelidon pyrrhonota ) has relatively recently shifted to almost exclusive use of artificial structures such as bridges and highway culverts for nesting and consequently has been exposed to higher levels of parasitism than on its ancestral cliff nesting sites. We examined whether increased ectoparasitism may have favored recent changes in the extent of the maxillary overhang. Using a specimen collection of cliff swallows from western Nebraska, USA, spanning 40 years and field data on live birds, we found that the extent of the maxillary overhang increased across years in a nonlinear way, peaking in the late 2000’s, and varied inversely with cliff swallow colony size for unknown reasons. The number of fleas on nestling cliff swallows declined in general over this period. Those birds with perceptible overhangs had fewer swallow bugs on the outside of their nest, but they did not have higher nesting success than birds with no overhangs. The intraspecific variation in the maxillary overhang in cliff swallows was partly consistent with it having a functional role in combatting ectoparasites. The temporal increase in the extent of the overhang may be a response by cliff swallows to their relatively recent increased exposure to parasitism. Our results demonstrate that this avian morphological trait can change rapidly over time. 

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2. Conservation Measures to Increase Breeding Success of Cliff Swallows (Petrochelidon pyrrhonota) in Massachusetts

   https://doi.org/10.1656/045.028.0212  

   Silver, M. (January 2021, Northeastern naturalist)

   Petrochelidon pyrrhonota (Cliff Swallow) is experiencing significant population declines in parts of its breeding range, particularly in northeastern North America. At 12 active Cliff Swallow colonies in western Massachusetts in 2019–2020, we examined the extent to which installation of artificial nests, providing of mud sources, and control of Passer domesticus (House Sparrow) affected colony size and reproductive success of Cliff Swallows. While there was a trend for colony size to increase at sites with artificial nests, there was not a significant size increase at these sites from 2019–2020. Cliff Swallow nesting success was significantly lower at colony sites where House Sparrows were present, compared to those at which they were absent. The number of nesting Cliff Swallows at 2 sites where mud sources were enhanced increased from 2019 to 2020. Efforts to control House Sparrows by shooting at 1 site were unsuccessful. Our study suggests that without effective control of House Sparrows, Cliff Swallows are likely to keep declining in Massachusetts, regardless of other management techniques used. 

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3. Birds of a Feather Flock Together: Extent of Long-Term Consistency of Colony-Size Choice in Cliff Swallows

   https://doi.org/10.3389/fevo.2022.860407  

   Brown, Charles R.; Hannebaum, Stacey L. (March 2022, Frontiers in Ecology and Evolution)

   Explaining why animal groups vary in size is a fundamental problem in behavioral ecology. One hypothesis is that life-history differences among individuals lead to sorting of phenotypes into groups of different sizes where each individual does best. This hypothesis predicts that individuals should be relatively consistent in their use of particular group sizes across time. Little is known about whether animals’ choice of group size is repeatable across their lives, especially in long-lived species. We studied consistency in choice of breeding-colony size in colonially nesting cliff swallows ( Petrochelidon pyrrhonota ) in western Nebraska, United States, over a 32-year period, following 6,296 birds for at least four breeding seasons. Formal repeatability of size choice for the population was about 0.41. About 45% of individuals were relatively consistent in choice of colony size, while about 40% varied widely in the colony size they occupied. Birds using the smaller and larger colonies appeared more consistent in size use than birds occupying more intermediate sized colonies. Consistency in colony size was also influenced by whether a bird used the same physical colony site each year and whether the site had been fumigated to remove ectoparasites. The difference between the final and initial colony sizes for an individual, a measure of the net change in its colony size over its life, did not significantly depart from 0 for the dataset as a whole. However, different year-cohorts did show significant net change in colony size, both positive and negative, that may have reflected fluctuating selection on colony size among years based on climatic conditions. The results support phenotypic sorting as an explanation for group size variation, although cliff swallows also likely use past experience at a given site and the extent of ectoparasitism to select breeding colonies. 

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4. The influence of subcolony-scale nesting habitat on the reproductive success of Adélie penguins

   https://doi.org/10.1038/s41598-021-94861-7  

   Schmidt, Annie E.; Ballard, Grant; Lescroël, Amélie; Dugger, Katie M.; Jongsomjit, Dennis; Elrod, Megan L.; Ainley, David G. (December 2021, Scientific Reports)

   null (Ed.)

   Abstract Group-size variation is common in colonially breeding species, including seabirds, whose breeding colonies can vary in size by several orders of magnitude. Seabirds are some of the most threatened marine taxa and understanding the drivers of colony size variation is more important than ever. Reproductive success is an important demographic parameter that can impact colony size, and it varies in association with a number of factors, including nesting habitat quality. Within colonies, seabirds often aggregate into distinct groups or subcolonies that may vary in quality. We used data from two colonies of Adélie penguins 73 km apart on Ross Island, Antarctica, one large and one small to investigate (1) How subcolony habitat characteristics influence reproductive success and (2) How these relationships differ at a small (Cape Royds) and large (Cape Crozier) colony with different terrain characteristics. Subcolonies were characterized using terrain attributes (elevation, slope aspect, slope steepness, wind shelter, flow accumulation), as well group characteristics (area/size, perimeter-to-area ratio, and proximity to nest predators). Reproductive success was higher and less variable at the larger colony while subcolony characteristics explained more of the variance in reproductive success at the small colony. The most important variable influencing subcolony quality at both colonies was perimeter-to-area ratio, likely reflecting the importance of nest predation by south polar skuas along subcolony edges. The small colony contained a higher proportion of edge nests thus higher potential impact from skua nest predation. Stochastic environmental events may facilitate smaller colonies becoming “trapped” by nest predation: a rapid decline in the number of breeding individuals may increase the proportion of edge nests, leading to higher relative nest predation and hindering population recovery. Several terrain covariates were retained in the final models but which variables, the shapes of the relationships, and importance varied between colonies. 

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5. Social foraging and the associated benefits of group‐living in C liff S wallows decrease over 40 years

   https://doi.org/10.1002/ecm.1602  

   Brown, Charles R; Brown, Mary B; Hannebaum, Stacey L; Wagnon, Gigi S; Pletcher, Olivia M; Page, Catherine E; West, Amy C; O'Brien, Valerie A (May 2024, Ecological Monographs)

   Abstract Animals that feed socially can sometimes better locate prey, often by transferring information about food that is patchy, dense, and temporally and spatially unpredictable. Information transfer is a potential benefit of living in breeding colonies where unsuccessful foragers can more readily locate successful ones and thereby improve feeding efficiency. Most studies on social foraging have been short term, and how long‐term environmental change affects both foraging strategies and the associated benefits of coloniality is generally unknown. In the colonial Cliff Swallow (Petrochelidon pyrrhonota), we examined how social foraging, information transfer, and feeding ecology changed over a 40‐year period in western Nebraska. Relative to the 1980s, Cliff Swallows in 2016–2022 were more likely to forage solitarily or in smaller groups, spent less time foraging, were more successful as solitaries, fed in more variable locations, and engaged less in information transfer at the colony site. The total mass of insects brought back to nestlings per parental visit declined over the study. The diversity of insect families captured increased over time, and some insect taxa dropped out of the diet, although the three most common insect families remained the same over the decades. Nestling Cliff Swallow body mass at 10 days of age and the number of nestlings surviving per nest declined more sharply with colony size in 2015–2022 than in 1984–1991 at sites where the confounding effects of ectoparasites were removed. Adult body mass during the provisioning of nestlings was lower in more recent years, but the change did not vary with colony size. The reason(s) for the reduction in social foraging and information transfer over time is unclear, but the consequence is that colonial nesting may no longer offer the same fitness advantages for Cliff Swallows as in the 1980s. The results illustrate the flexibility of foraging behavior and dynamic shifts in the potential selective pressures for group living. 

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