Biology subjects

Reichard, D. G.

Publications and source records attributed to Reichard, D. G..

8 recordsLinked to original sources

bioRxiv2025

Predator type and relative risk affects the repeatability of nest defense in a songbird

Interindividual differences in nest defense towards a single predator type have been shown to be repeatable in multiple species, supporting the presence of personality. Here, we assessed if the nest defense of female northern house wrens (Troglodytes aedon) was repeatable across different types of predators, which is predicted by personality and largely untested. Over three years, we placed a decoy of a common nest predator, the eastern rat snake (Pantherophis alleghaniensis), on top of nest boxes and measured female behavior. Each season, we also presented a second stimulus of varying threat level, including an eastern chipmunk decoy (Tamias striatus), a taxidermied Coopers hawk (Accipiter cooperii), and a novel object of unknown threat. We measured repeatability between each pair of threats and compared the population-level response to the snake across years. Nest defense was significantly repeatable between the snake and chipmunk, which presented similar risks. It was also repeatable between the snake and novel object despite the population-level response to the object being significantly weaker. In contrast, nest defense was not repeatable between the snake and the hawk, which posed a significant threat to adult survival that may have disrupted the consistency of the female response. Finally, the average, population-level response to the snake did not detectably differ among years, indicating stability in this behavior despite high turnover in breeding adults. These results suggest the presence of personality in nest defense, but more research is needed to evaluate the effect of high-risk predators on the repeatability of this behavior. Significance StatementDifferences among individuals in the strength of nest defense are often repeatable towards a specific predator, indicating the presence of personality. However, few studies have tested the repeatability of nest defense across different predators of varying threat levels. Personality predicts that weak/strong responders to one predator should also be weak/strong to another. We tested this prediction in female northern house wrens by placing decoys of different predators and a novel object on top of their nest boxes to measure nest defense. Nest defense was repeatable between two predators of similar risk and between a predator and a novel object of unknown risk. However, nest defense was not repeatable between a low and high-risk predator. The results suggest the presence of personality, but research is needed on the effects of high-risk predators that appear to disrupt behavioral consistency.

animal behavior and cognition↗

bioRxiv2025

AI, citizen science, and the 2024 eclipse emphasize the importance of light for bird behavior

On April 8th 2024, a total solar eclipse disrupted light-dark cycles for North American birds during the lead-up to spring reproduction. Compiling over 10,000 community observations and AI analyses of nearly 100,000 vocalizations, we found that bird behavior was significantly affected by these few minutes of unexpected afternoon darkness. More than half of wild bird species changed their biological rhythms, with many producing a dawn chorus in the aftermath of the eclipse. This natural experiment demonstrates the power of technology-enabled and public science projects to understand our natural world. Further, it underscores the power of light in structuring animal behavior: even when night lasts for just four minutes, robust behavioral changes ensue.

animal behavior and cognition↗

bioRxiv2025

The effects of human presence, restraint, and stressed neighbors on corticosterone levels in domesticated budgerigars (Melopsittacus undulatus)

Limiting stress during interactions between captive animals and humans is important for effective husbandry. One physiological change during the vertebrate stress response is the release of glucocorticoid hormones. Here, we measured plasma corticosterone in female domesticated budgerigars (Melopsittacus undulatus) to test whether human presence, restraint, or removal and return of a newly stressed neighbor increases corticosterone. The presence of humans for 15 minutes at the beginning of the experiment did not significantly elevate corticosterone above baseline levels, suggesting that birds that acclimate to humans are minimally affected by their presence. However, at the end of the experiment after multiple blood sampling events, the same human presence test significantly elevated corticosterone above baseline and human presence levels measured at the beginning of the experiment. Thus, repeated blood sampling could cause progressively stronger stress responses to human presence. Restraint-induced corticosterone levels were significantly higher than all other treatments, indicating that human handling activates the stress response. After stressed birds were returned home, corticosterone levels of their neighbors were significantly higher than baseline at 25- and 45-minutes post-return. However, the 25- and 45-minute corticosterone levels were not significantly different from each other, or levels induced by human presence at the beginning or end of the experiment. This outcome suggests that social transmission of stress was limited across the sampled time frame. These data highlight the importance of evaluating the costs and benefits of different human-animal interactions in captivity, including in domesticated species that are more tolerant of forced proximity to humans. Research HighlightsO_LIHuman presence only elevated plasma corticosterone after multiple blood sampling events. C_LIO_LIRestraint significantly increased corticosterone levels relative to all other treatments. C_LIO_LIMinimal evidence for social transmission of stress. C_LI

zoology↗

bioRxiv2024

Repeatability of an extended phenotype: causes and consequences of nest variation in a free-living songbird

LAY SUMMARYO_LIRepeatability of construction behaviors in the wild is understudied C_LIO_LIHouse Wrens are a cavity-nesting songbird C_LIO_LIHouse Wren nests are highly variable in their morphology C_LIO_LIFemale House Wrens are repeatable in cup composition, but not nest dimensions C_LIO_LIThe dimensions of the nest are built to match the dimensions of the cavity C_LIO_LIHouse Wren nests are unrelated to nestling survival or female condition C_LIO_LIFemale preferences for nest building may explain nest variation C_LI Construction behavior is an aspect of the extended phenotype that allows organisms to build structures that alter their environments in potentially beneficial ways. Although individuals vary in the expression of this extended phenotype (e.g., structure morphology), the repeatability of construction behaviors remain understudied, especially among free-living populations. Many oviparous taxa construct nests, making them of particular interest because variation in nest architecture may directly affect fitness. Using a free-living, cavity-nesting songbird, the Northern House Wren (Troglodytes aedon aedon), as our model, we estimated the contribution of the primary builder (the female) to nest variability by measuring the repeatability of nest morphology between successive clutches. We further examined whether nest morphology was related to the dimensions of the nesting cavity, breeding date, or nest success. We found the composition of the cup lining to be a highly repeatable behavior for the nesting female, although the size and composition of the structural platform appeared more related to the dimensions of the cavity. Nest morphology remained variable throughout the breeding season, showing no significant correlations with breeding date, and it was unrelated to clutch size or offspring survival. Our study suggests that variation in construction behavior is likely the product of multiple factors including the preferences of the builder and physical constraints. The absence of any clear links between construction behavior and fitness indicates that nest morphology is not under strong selection. As a result, diverse female building preferences may explain the extreme among-individual variation in nest structure in this species.

animal behavior and cognition↗

bioRxiv2023

Risk assessment during nest defense against three simulated predators by female northern house wrens (Troglodytes aedon aedon)

Offspring predation is one of the greatest obstacles to an organisms reproductive success, but parents vary in the strength of their response to potential predators. One explanation for this variable investment is that defending current offspring has the potential to lower future reproductive success if the predator is also capable of injuring or killing the parent. Northern house wrens (Troglodytes aedon) are cavity-nesting songbirds that defend against multiple species of nest predators including small mammals, birds of prey, and snakes. Here, we used three different predator decoys: two nest predators - an eastern chipmunk (Tamias striatus) and an eastern ratsnake (Pantherophis alleghaniensis) - as well as a predator of both offspring and adults - a juvenile Coopers hawk (Accipiter cooperi) - to elicit nest defense and test whether females use risk assessment to modulate their antipredator behavior. We found that antipredator behaviors were not significantly different between the two nest predators, which posed a high risk to the nestlings, but lower risk to the parents as neither species frequently captures adult wrens outside the nest box. However, female wrens never dove at or attacked the Coopers hawk while they frequently attacked both the snake and chipmunk decoys. Neighboring house wrens from adjacent territories were also less likely to respond to the hawk, but more heterospecifics mobbed the hawk than the snake decoy. Collectively, these results show that risk assessment and the strength of the antipredator response varies substantially both within and among species. Female house wrens exhibit plasticity in their nest defense behavior, and they respond to different types of predators in a way that could maximize lifetime fitness while risking the loss of their current offspring.

evolutionary biology↗

bioRxiv2021

Seasonal song variation in male Carolina Wrens (Thryothorus ludovicianus)

Birdsongs primary function is attracting and stimulating mates and repelling rivals during the breeding season. However, many species also sing during the nonbreeding season, which raises questions about the function of nonbreeding song and the proximate mechanisms underlying its production. In this study, we compared spectral and temporal measurements from a large sample of breeding (N = 267) and nonbreeding songs (N = 283) of Carolina Wrens (Thryothorus ludovicianus), a nonmigratory, temperate species that sings year-round. We found that breeding songs were longer than nonbreeding songs and had more syllables within each song. Trill rate, the number of notes per syllable, minimum and maximum frequency and frequency bandwidth did not differ detectably between the two seasons. This study is the first to examine seasonal song differences in Carolina Wrens and provides a basis for future investigations into the drivers behind this seasonal variation.

animal behavior and cognition↗

bioRxiv2019

Urban birdsongs: higher minimum song frequency of an urban colonist persists in a common garden experiment

Environmental changes caused by urbanization and noise pollution can have profound effects on acoustic communication. Many organisms use higher sound frequencies in urban environments with low-frequency noise, but the developmental and evolutionary mechanisms underlying these shifts are less clear. We used a common garden experiment to ask whether changes in minimum song frequency observed 30 years after a songbird colonized an urban environment are a consequence of behavioral flexibility or canalized changes that occur early in development. We captured male juvenile dark-eyed juncos (Junco hyemalis thurberi) from two recently diverged populations (urban and mountain) soon after they reached independence (aged 25-40 days), raised them in identical indoor aviaries, and studied their songs at an age of three years. We found that the large population difference in minimum frequency observed in the field persisted undiminished in the common garden despite the absence of noise. We also found some song sharing between the common garden and natal field populations, indicating that early song memorization before capture could contribute to the persistent song differences in adulthood. These results are the first to show that frequency shifts in urban birdsong are maintained in the absence of noise by genetic evolution and/or early life experiences.

evolutionary biology↗

bioRxiv2019

Patterns of annual and seasonal immune investment in a temporal reproductive opportunist

Historically, investigations of how organisms investments in immunity fluctuate in response to environmental and physiological changes have focused on seasonally breeding organisms that confine reproduction to seasons with mild environmental conditions and abundant resources. Consequently, knowledge of how harsh environmental conditions and reproductive effort may interact to shape investment in immunity remains limited. The red crossbill, Loxia curvirostra, is a songbird that can breed on both short, cold and long, warm days if conifer seeds are abundant. This species provides an ideal system to investigate the influence of environmental fluctuations, reproductive investment, and their potential interactions on patterns of immune investment. In this study, we measured inter- and intra-annual immune variation in crossbills across four consecutive summers (2010-2013) and multiple seasons within one year (summer 2011-spring 2012) to explore how physiological and environmental factors impact this immune variation. Overall, the data suggest that immunity varies seasonally, among years, and in response to environmental fluctuations in food resources, precipitation, and temperature, but less in response to physiological measures such as reproduction. Collectively, this system demonstrates that a reproductively flexible organism may breed when conditions allow simultaneous investment in survival-related processes rather than at the expense of them.

ecology↗