Knemidokoptic mite infestation of island populations of Red-winged Blackbirds (Agelaius phoeniceus)
J.S. Marshall and S.K. Winnicki. In press for Wilson Journal of Ornithology
Knemidokoptic mites infest a number of bird species around the world and may lead to decreased survival, although relatively few studies have documented long-term effects on populations. We present 9 years of data monitoring the survival of Red-winged Blackbirds (Agelaius phoeniceus) in the Lake Erie, Ohio, USA islands. Blackbirds in our study first appeared with mite infestation in 2012. Percentage of the total number of blackbirds infested with mites peaked at 7.3% in 2013 and persisted at between 5 and 6% through the summer of 2018. We saw no differences in infestation rates based on blackbird sex or age. Unlike most other studies, we did recapture birds that had previously had infestations, and we detected no decline in recapture rate due to mite infestation. While that does not mean that blackbirds do not experience negative consequences of infestation, our evidence does suggest that low level infestation may be persistent in a population without dramatic declines in survivorship.
Ground-nesting by arboreal American robins (Turdus migratorius)
S.K. Winnicki, M.E. Hauber, T.J. Benson, and M. Abolins-Abols, check it out here!
Animals with dependent and vulnerable young need to decide where to raise their offspring to minimize ill effects of weather, competition, parasitism, and predation. These decisions have critical fitness consequences through impacting the survival of both adults and progeny. Birds routinely place their nest in specific sites, allowing species to be broadly classified based on nest location (e.g., ground- or tree-nesting). However, from 2018 to 2020, we observed 24 American robin (Turdus migratorius) nests placed not on their species-typical arboreal substrates or human-made structures but on the ground at a predator-rich commercial tree-farm in Illinois, USA. This behavior does not appear to be in response to competition and did not affect nest daily survival rate but was restricted to the early half of the breeding season. We hypothesize that ground nesting may be an adaptive response to avoid exposure and colder temperatures at sites above the ground early in the breeding season or a nonadaptive consequence of latent robin nest-placement flexibility.
Effects of patch-burn grazing on reproductive success of grassland songbirds
B.H.F. Verheijen, A.N. Erickson, W.A. Boyle, K.S. Leveritte, J.L. Sojka, L.A. Spahr, C.C. Tehn, E.J. Williams, S.K. Winnicki, and B.K. Sandercock, check it out here!
Referential alarm calling elicits future vigilance in a host of an avian brood parasite
Yellow warblers (Setophaga petechia) use referential ‘seet’ calls to warn mates of brood parasitic brown-headed cowbirds (Molothrus ater). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by seet calls on one day, extend their anti-parasitic responses into the future by engaging in vigilance at sunrise on the next day, when parasitism may occur. As predicted, daytime seet call playbacks caused female warblers to leave their nests less often on the following morning, relative to playbacks of both their generic anti-predator calls and silent controls. Thus, referential calls do not only convey the identity or the type of threat at present but also elicit vigilance in the future to provide protection from threats during periods of heightened vulnerability.
Developmental asynchrony and host species identity predict variability in nestling growth of an obligate brood parasite: a test of the “growth-tuning” hypothesis
Canadian Journal of Zoology: coauthors B.M. Strausberger, N.D. Antonson, D.E. Burhans, J. Lock, A.M. Kilpatrick, and M.E. Hauber, check it out here!
Generalist obligate brood parasites are excellent models for studies of developmental plasticity, as they experience a range of social and environmental variation when raised by one of their many hosts. Parasitic Brown-headed Cowbirds (Molothrus ater (Boddaert, 1783)) exhibit host-specific growth rates, yet cowbird growth rates are not predicted by hosts’ incubation or brooding periods. We tested the novel “growth-tuning” hypothesis which predicts that total asynchrony between cowbirds’ and hosts’ nesting periods results in faster parasitic growth in nests where host young fledge earlier than cowbirds. We tested this prediction using previously-published and newly-added nestling mass data across diverse host species. Total nesting period asynchrony (summed across incubation and brooding stages) predicted cowbird growth; 8-day old cowbirds were heavier in host nests with relatively shorter nesting periods. We further explored the drivers of variation in growth using mass measurements of cowbirds in Song Sparrow (Melospiza melodia (Wilson, 1810)) and Red-winged Blackbird (Agelaius phoeniceus (Linnaeus, 1766)) nests. Our top models included host species (cowbirds grew faster in sparrow nests), numbers of nestmates (slowest when raised alone), and sex (males grew faster). These results confirm that multiple social and environmental factors predict directional patterns of developmental plasticity in avian generalist brood parasites.
The limits of egg recognition: testing acceptance thresholds of American robins in response to decreasingly egg-shaped objects in the nest
Mark E. Hauber, Sarah K. Winnicki*, Jeffrey P. Hoover, Daniel Hanley and Ian R. Hays
Social interactions do not drive territory aggregation in a grassland songbird
Ecology 2020, coauthors: S.M. Munguía, E.J. Williams, and W.A. Boyle
Understanding the drivers of animal distributions is a fundamental goal of ecology and informs habitat management. The costs and benefits of colonial aggregations in animals are well established, but the factors leading to aggregation in territorial animals remain unclear. Territorial animals might aggregate to facilitate social behavior such as (1) group defense from predators and/or parasites, (2) cooperative care of offspring, (3) extra-pair mating, and/or (4) mitigation of extra-pair mating costs through kin selection. Using experimental and observational methods, we tested predictions of all four hypotheses in a tallgrass prairie in northeast Kansas, United States. Grasshopper Sparrow (Ammodramus savannarum) males formed clumps of territories in some parts of the site while leaving other apparently suitable areas unoccupied. Despite substantial sampling effort (653 territories and 223 nests), we found no support for any hypothesized social driver of aggregation, nor evidence that aggregation increases nest success. Our results run counter to previous evidence that conspecific interactions shape territory distributions. These results suggest one of the following alternatives: (1) the benefits of aggregation accrue to different life‐history stages, or (2) the benefits of territory aggregation may be too small to detect in short‐term studies and/or the consequences of aggregation are sufficiently temporally and spatially variable that they do not always appear to be locally adaptive, perhaps exacerbated by changing landscape contexts and declining population sizes. Check it out here!
The impact of maternal hormones on the growth and development of birds
(fondly known on Twitter as project #GrowBirdGrow)
We are investigating the ways in which the hormones passed from mom to egg ultimately influence the growth and behavior of bird embryos, chicks, and juveniles. Keep checking in using the @GrowBirdGrow Twitter as I update everyone on our progress!
The role of brood parasitism in shaping nestling growth and development strategies
(fondly known on Twitter as project #PrairieBabies)
In my master’s research, I seek to identify the effect(s) of Brown-headed Cowbird (Molothrus ater) brood parasitism on the growth and development of nestlings of three grassland-obligate host species: Grasshopper Sparrow (Ammodramus savannarum), Dickcissel (Spiza americana), and Eastern Meadowlark (Sturnella magna). Previous work on nestling development has illustrated the importance of perceived nest predation risk (e.g. Cheng and Martin 2012) and food availability (e.g. Ricklefs 1993)—in order to identify the variation explained by cowbird parasitism, we need to quantify the effect(s) of and interactions between food availability and predation risk as well. We will locate nests of each of the host species and identify the perceived predation risk, the food available to the nestlings, and the presence and risk of cowbirds at subsets of the total nests. We will then relate these factors to the skeletal growth, development (eyes opening, movement capacity), feather growth, and fat/muscle gain of the host nestlings, which we will calculate from nestling measurements taken every other day. At the conclusion of this study we hope to advance our knowledge of the impact of cowbirds, identify the development strategies that produce highest nest and post-fledge success in cowbird-dominated systems, and provide insight on the past and future evolution of cowbird hosts.
The Ideals of Female Sanctity in Merovingian and Carolingian Vitae
My undergraduate history research explored the ways that "holiness" was expressed in texts from Merovingian and Carolingian Gaul (5th-8th century, modern-day France). These saints' lives, or vitae, were written to commemorate the lives of and campaign for the canonization of deceased individuals. As such, they do not provide us with stories of historical reality, but rather give us insight into the values of the writers at the time. Therefore, I use vitae of female saints (especially the pretty awesome St. Radegund and St. Genovefa) to explore the ways gender identity interacted with religion; what language and motifs were acceptable ways to portray women's holiness? How did that change over time? How did gender and religion interact with other sociopolitical realities at the time? Ultimately I argued that these vitae portray a shift from warrior-like, action-based valor stories to passive, introspective piety as time progressed. This change mirrored the rise of the Church in Gaul; in the early Merovingian dynasty the spreading Church valued miraculous visible saints of all genders, representing the power of Christianity to the masses as the Church expanded. By the end of the Carolingian dynasty Christianity was firmly established in Gaul--at this point the Church did not need saints who showcased the incredible power of the religion, but rather saints who exhibited quiet, pious deference to the Church hierarchy. Please note that I have not revised this in years-- there are likely problematic references to a gender binary throughout the text. Read it here by clicking on the purple box!