Differences in adrenocortical responses between urban and rural burrowing owls: poorly-known underlying mechanisms and their implications for conservation

Abstract

<jats:title>Abstract</jats:title> <jats:p>The hypothalamus–pituitary–adrenal/interrenal (HPA) axis of vertebrates integrates external information and orchestrates responses to cope with energy-demanding and stressful events through changes in circulating glucocorticoid levels. Urbanization exposes animals to a wide variety of ever-changing stimuli caused by human activities that may affect local wildlife populations. Here, we empirically tested the hypothesis that urban and rural owls (Athene cunicularia) show different adrenocortical responses to stress, with urban individuals showing a reduced HPA-axis response compared to rural counterparts to cope with the high levels of human disturbance typical of urban areas. We applied a standard capture-restraint protocol to measure baseline levels and stress-induced corticosterone (CORT) responses. Urban and rural owls showed similar circulating baseline CORT levels. However, maximum CORT levels were attained earlier and were of lower magnitude in urban compared to rural owls, which showed a more pronounced and long-lasting response. Variability in CORT responses was also greater in rural owls and contained the narrower variability displayed by urban ones. These results suggest that only individuals expressing low-HPA-axis responses can thrive in cities, a pattern potentially mediated by three alternative and non-exclusive hypotheses: phenotypic plasticity, natural selection and matching habitat choice. Due to their different conservation implications, we recommend further research to properly understand wildlife responses to humans in an increasingly urbanized world.</jats:p>

Drivers of the Ectoparasite Community and Co-Infection Patterns in Rural and Urban Burrowing Owls

“…In addition, the permanence of a large number of nestlings inside the nests (we observed nests with up to 5–7 fledglings) during their first weeks of life may favor parasitization and parasite exchange between siblings. Further research is needed to understand whether these results may be also due to the lower immunocompetence of nestlings, or to the better nutritional state of adults, or if it is related to other environment or behavioral factors not considered here [ 42 ].…”

“…The number of individuals occupying each nest, i.e., breeders, nestlings, and individuals delaying dispersal [ 48 ], was obtained by intense monitoring throughout the breeding season [ 36 , 45 ]. The sex of adults was assigned by plumage pattern coloration [ 60 ] or, when needed for adults and nestlings, by molecular procedures using blood samples [ 42 ].…”

“…However, changes in conspecific density, resource availability and predation pressure commonly found in urban ecosystems [ 27 , 31 , 32 , 33 ] can have both positive and negative effects on the breeding performance and survival prospects of individuals [ 34 , 35 , 36 ]. Urbanization may also affect the parasite-host interactions by providing some effective resources to deal with ectoparasites: e.g., using cigarette butts within the nest material reduce the ectoparasite load in birds [ 37 ], or by increasing stress [ 38 ]: e.g., heavy metals [ 39 ], noise [ 40 ], human disturbance [ 41 ], but see [ 35 ], which can affect the body condition and health status of the individuals [ 42 ]. Thus, urban individuals can differ in their propensity to be parasitized compared to their rural counterparts.…”

Human protection drives the emergence of a new coping style in animals

“…Concerning the stress responses, results are less consistent, and 2 opposite patterns were described in response to urbanization. Some studies observed a reduced stress load or stress response [40,[44][45][46], while others highlighted increased post-stress corticosterone production [47,48] or increased heart rates [49] in urban animals (Fig 1. Urban (i) and Urban (ii)) [50].…”

Life history trade-offs in glucocorticoid-mediated habitat selection

“…Initially, selection of different habitats may be driven by chance variation in response to the environment among individuals (Bolnick et al, 2003). But because individuals are exposed to different stressors in the habitats they occupy, that chance variation in habitat use could also shape subsequent glucocorticoid production (Palma et al, 2020). Disruptive selection on both glucocorticoid profiles and habitat selection would then reinforce trade-offs between reproduction and survival by different individuals, resulting in both the physiological and spatial separation of populations over time (Lema, 2020).…”