Avian behavior in a changing world: how human effects change behavioral expression at the individual, population, and community level

Abstract

Human induced rapid environmental change (HIREC) is one of the largest threats to avian biodiversity and abundance (Rosenberg et al. 2019; Sih, Ferrari, and Harris 2011). Since selection acts on individual behavioral variation first, understanding which behavioral phenotypes are favored under these new selection pressures is necessary to understand how HIREC will eventually affect populations and communities (Alley et al. 2003; Bergstrom et al. 2015). With climate change acting so quickly, organisms have little time to respond and adapt to the novel conditions they face (Radchuk et al. 2019; Sih 2013). Under these altered conditions, selection may favor behavioral phenotypes that are maladaptive, such as individuals favoring a resource that lowers fitness, i.e. an ecological trap (Dwernychuk and Boag 1972; Robertson, Rehage, and Sih 2013). Understanding how maladaptive behaviors are selected from a spectrum of available behavioral phenotypes can help us reduce trap susceptibility and potentially even prevent ecological traps from occurring. Behavioral plasticity is necessary for an individual adjust to HIREC to avoid fitness loss and death. Understanding how phenotypic plasticity responds to a changing environment can aid us in understanding how these individuals will persist in HIREC. However, we do not know the limits of behavioral flexibility under these extremely altered conditions. While activational behavioral plasticity (i.e. behavioral flexibility) can help individuals respond to immediate extreme events, developmental plasticity (i.e. plasticity) can limit the types or number of responses an individual can produce (Buchholz et al. 2019; Both et al. 2004). Understanding these behavioral flexibility and plasticity limits can help us understand how individuals can mitigate the negative consequences of HIREC and give us an idea of future trait selection. This dissertation focused on how HIREC will affect avian behavioral responses, at the individual, population, community level in birds. My first chapter focuses on the effects of elevated noise levels on avian parental care and nestling development in eastern bluebirds (Sialia sialis). Anthropogenic noise is a ubiquitous feature of the American landscape, and is a known stressor for many bird species, leading to negative effects in behavior, physiology, reproduction, and ultimately fitness. While many studies examined how anthropogenic noise affects avian fitness, few also examined how noise impacts the relationship between parental care behavior and nestling fitness. We conducted Brownian noise playbacks for six hours a day during the nesting cycle on Eastern Bluebird (Sialia sialis) nest boxes to investigate if experimentally elevated noise affected parental care behavior, nestling body conditions, and nestling stress indices. We documented nest attendance by adult females using radio frequency identification (RFID), and we assessed nestling stress by measuring baseline corticosterone levels and telomere lengths. Adult bluebirds exposed to noise had significantly higher feeding rates earlier in the brood cycle than adults in the control group, but reduced feeding rates later in the cycle. Nestlings exposed to noise had higher body conditions than the control nestlings at eleven days of age, but conditions equalized between treatments by day fourteen. We found no differences in nestling baseline corticosterone levels or nestling telomere lengths between the two treatment groups. Our results revealed that noise altered adult behavior, which corresponded with altered nestling body condition. However, the absence of indicators of longer-term effects of noise on offspring suggests adult behavior may have been a short-term response. My second chapter focused on simulating how current and future climate conditions alter avian soundscapes using agent-based models, and how individual vocalizing behavior can impact the entire population. Climate change is increasing aridity in grassland and desert habitats across the southwestern United States, reducing available resources and drastically changing the breeding habitat of many bird species. Increases in aridity will reduce sound propagation distances, potentially impacting habitat soundscapes, and leading to a breakdown of the avian soundscapes, which could lead to the loss of vocal culture, reduced mating opportunities, and local population extinctions. We developed an agent-based model to examine how changes in aridity will affect both sound propagation and the ability of territorial birds to audibly contact their neighbors. We simulated vocal signal attenuation under a variety of environmental scenarios for the south central semi-arid prairies of the United States, ranging from contemporary weather conditions to predicted extremes under climate change. We also simulated how changes in physiological conditions, mainly evaporative water loss (EWL) would affect singing behavior. Under extreme climate change conditions, we found significantly fewer individuals successfully contacted all adjacent neighbors than did individuals in either the contemporary or mean climate change conditions. We also found that at higher sound frequencies and higher EWL, fewer individuals were able to successfully contact all of their neighbors, particularly in the extreme and extreme climate change conditions. These results indicate that climate change-mediated aridification may disrupt the avian soundscape, such that vocal communication no longer effectively functions for mate attraction or territorial defense. As climate change progresses increased aridity in current grasslands may favor shifts toward low frequency songs, colonial resource use, and altered songbird community compositions. My third and final chapter tested the conclusions outlined in chapter 2 on how avian singing activity and species composition vary across local climate conditions and access to water resources. Climate change is increasing aridity across multiple habitats throughout the world, which is likely reducing critical resources for songbirds in environments that are already resource limited. In addition to reducing food and water availability, increased aridity can reduce sound transmission distances and impose stress in the form of evaporative water loss on singing birds. To determine how aridity and water access affect avian vocal activity and detectability, we used automated recording units (ARUs) to sample soundscapes in shrub- and grassland ecosystems across an aridity gradient in Oklahoma, Texas, and New Mexico. We also examined the effect of water availability experimentally by providing supplemental water in two of the study sites. Avian vocal behavior decreased with increasing aridity across sites but was consistent across the morning acoustic period. Supplemental water did lead to increased detectable vocal behavior during arid conditions but only in one of the supplemental water experiments. During extremely arid conditions, only the most arid sites demonstrated significant negative responses, indicating these communities have some resilience to increasing aridity. Reduced vocal communication due to high aridity could be a warning sign of at-risk avian communities in some arid environments. Future studies should focus on how community composition and vocal characteristics change under increasing aridity.