Swanson, Z. M. | bioRxiv Science

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↗

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↗