Frederick Verbruggen

The expansion of human activities has increased the need for animal rehabilitation, especially for urban-breeding species such as herring gulls (Larus argentatus) and lesser black-backed gulls (Larus fuscus), which now commonly nest on buildings and industrial sites. This study evaluates rehabilitation effectiveness by comparing survival and post-release reintegration, measured through habitat use and the degree of association with human-dominated environments, between rehabilitated and wild juvenile gulls along the Belgian coast. From 2012 to 2023, 3443 juveniles were ringed and monitored. Estimated apparent survival varied with age and species and was broadly similar between rehabilitated and wild birds, although rehabilitated lesser black-backed gulls showed slightly lower apparent survival than their wild counterparts. Differences in habitat use and association with local human population density were largely confined to juveniles: rehabilitated juveniles were resighted more often in intertidal areas with lower human population densities, with patterns converging in older age classes. Our results suggest rehabilitation can support urban gull populations by yielding broadly wild-like apparent survival.

Ring-necked parakeets (Psittacula krameri) are among the most successful avian invaders in Europe. Since their establishment in the 1970s, populations have expanded across the continent, with urban areas serving as primary strongholds. Despite growing concern over their ecological impacts, including competition with native cavity-nesting species and agricultural damage, fine-scale information on how breeding individuals use urban landscapes remains limited. Understanding space use and habitat selection during the breeding season is essential for predicting further range expansion and informing management strategies. Here, we present the preliminary results of an ongoing GPS telemetry study investigating the spatial ecology of breeding ring-necked parakeets in the city of Antwerp, Belgium. Individual parakeets were captured at breeding sites using mist nets deployed near active nest cavities. Birds were fitted with lightweight solar-powered GPS transmitters (~5 g) attached via Teflon harnesses. Tags were programmed to record locations throughout the breeding period (April–June), which mainly corresponds to the chick-rearing period. Concurrent with the telemetry work, we conduct standardized field observations at sites identified from GPS fixes and at matched comparison sites across the urban landscape. At each site, we record resource availability through systematic surveys of the nearest trees and their phenological state, and collect focal behavioral observations of foraging parakeets. This links individual movement patterns to fine-scale habitat characteristics and food resource availability. Our analysis characterizes the relationship between urbanization gradients and space use, specifically determining the extent to which home range size and foraging selectivity vary across different habitat configurations. We examine how the concentration of food resources influences the trade-off between commute distances and quality of foraging sites.

Urbanization is transforming the breeding habitats of many bird species. Key urban features, such as elevated temperatures, poor water drainage, altered predator communities, including cats, and the presence of anthropogenic food sources, such as human waste, can influence the risk of embryo mortality and alter parental care, particularly in open-nesting species. Parents may adjust incubation behavior to buffer embryos against these conditions, but whether this suffices to maintain reproductive success remains unclear. We investigated how rooftop breeding affects incubation behavior and reproductive success in Larus argentatus (Herring Gull) by comparing rooftop- and ground-nesting pairs across 2 breeding seasons in Belgium. Using temperature loggers placed in artificial eggs, we quantified daily off-bout frequency and duration with the incR package in 78 nests (2023: 11 ground, 15 rooftop; 2024: 22 ground, 30 rooftop). We predicted that rooftop-nesting pairs would reduce off-bout frequency and/or duration relative to ground-nesting pairs, thereby limiting egg exposure to environmental conditions. We further predicted that, if these adjustments effectively buffer embryos from rooftop stressors, hatching success would be comparable between environments. In line with our behavioral predictions, rooftop-nesting pairs took fewer off-bouts per day than ground-nesting pairs, particularly in 2024 (2024 ground/rooftop ratio = 3.49, 95% CI: 2.28–5.34), whereas off-bout duration did not differ. However, hatching success was lower in rooftop nests, even after excluding egg predation or breakage (odds ratio = 0.05, 95% CI: 0.01–0.35), suggesting that the observed behavioral changes did not fully mitigate environmental stressors. Hatchling size was comparable across environments (mean head + bill size: rooftop = 47.77 ± 1.77 mm, ground = 47.84 ± 1.06 mm), indicating that differences in reproductive success were driven mainly by embryo mortality rather than altered embryonic growth. These findings suggest that urban rooftops impose incubation-stage challenges, altering incubation dynamics and breeding outcomes in open-nesting birds.

Global environmental changes alter the availability and predictability of marine resources, forcing marine predators to adapt their diets and foraging strategies. Lesser black‐backed gulls Larus fuscus exhibit individual differences in foraging consistency within and across years, which could influence reproductive success. Using stable isotope analysis (SIA) of chick feathers collected over three consecutive years (2021–2023), we examined whether year‐to‐year change in marine diet proportion within pairs, during the peak chick demand period, was reflected in the size of the chicks at fledging (head–bill size, tarsus length, and body mass). Despite an overall high marine dietary contribution of around 85%, pairs showing a greater year‐to‐year change in marine diet produced heavier chicks at fledging in the year with the lowest marine proportion. Our findings support the potential adaptive value of dietary flexibility under changing environmental conditions, highlighting the importance of long‐term monitoring for understanding seabird population resilience.

The post-fledging period is a critical phase for inexperienced birds, who must navigate and explore unfamiliar environments to locate essential resources for survival. Successful foraging during this stage relies on acquiring spatial knowledge through exploration, which may develop early in life. In this study, we examined whether the early-life exploratory phenotype, assessed through an open field test (OFT) during the nestling phase, predicts post-fledging behaviour and survival. GPS tracking data from 34 juvenile lesser black-backed gulls (Larus fuscus) over a 20-day period were used to quantify habitat preferences, spatial use (mean squared displacement and revisitation patterns) and time spent flying, foraging and resting. Survival was monitored over six months following fledging, encompassing migration. Early-life exploratory phenotype predicted habitat use: individuals with a more exploratory phenotype frequented urban habitats more often, whereas those with a less exploratory phenotype relied more on agricultural areas. However, exploratory phenotypes did not predict spatial use or survival. These findings indicate that behavioural variation established early in life can have lasting ecological consequences. The absence of a link between exploratory phenotype and survival may reflect phenotype–habitat matching, stochastic environmental factors, or that the OFT does not capture the behavioural components most relevant to survival.

Response inhibition - the ability to suppress or stop actions - is crucial for adaptive behaviour across species. In Part 1 of this study, we presented a conceptual framework for understanding response inhibition as multifaceted. Specifically, we conceptualised response inhibition as a race between a ‘go runner’ and a ‘stop runner’. These runners are modulated by the type of stimulus that triggers the runner, the relative timing between stimuli, and the type of actions that are elicited. In Part 2, the framework is used to make predictions about correlations between different measures of response inhibition across three tasks: the detour barrier task, the thwarting task, and the stop-change task. These predictions were tested in two closely related bird species: herring gulls ( Larus argentatus ) and lesser black-backed gulls ( Larus fuscus ). The correlations between specific measures of response inhibition were generally weak. This pattern of results supports the idea that response inhibition is not a unitary ability, but rather a set of partly independent components. These findings highlight the importance of task context and trigger type in shaping inhibitory performance, and they illustrate how conceptual and mathematical models can guide more nuanced interpretations of inhibition across different ecological and experimental settings.