Experimental nest cooling reveals dramatic effects of heatwaves on reproduction in a Mediterranean bird of prey

Future climatic scenarios forecast increases in average temperatures as well as in the frequency, duration, and intensity of extreme events, such as heatwaves. Whereas behavioral adjustments can buffer direct physiological and fitness costs of exposure to excessive temperature in wild animals, these may prove more difficult during specific life stages when vagility is reduced (e.g., early developmental stages). By means of a nest cooling experiment, we tested the effects of extreme temperatures on different stages of reproduction in a cavity-nesting Mediterranean bird of prey, the lesser kestrel (Falco naumanni), facing a recent increase in the frequency of heatwaves during its breeding season. Nest temperature in a group of nest boxes placed on roof terraces was reduced by shading them from direct sunlight in 2 consecutive years (2021 and 2022). We then compared hatching failure, mortality, and nestling morphology between shaded and non-shaded (control) nest boxes. Nest temperature in control nest boxes was on average 3.9 degrees C higher than in shaded ones during heatwaves, that is, spells of extreme air temperature (>37 degrees C for =2 consecutive days) which hit the study area during the nestling-rearing phase in both years. Hatching failure markedly increased with increasing nest temperature, rising above 50% when maximum nest temperatures exceeded 44 degrees C. Nestlings from control nest boxes showed higher mortality during heatwaves (55% vs. 10% in shaded nest boxes) and those that survived further showed impaired morphological growth (body mass and skeletal size). Hence, heatwaves occurring during the breeding period can have both strong lethal and sublethal impacts on different components of avian reproduction, from egg hatching to nestling growth. More broadly, these findings suggest that the projected future increases of summer temperatures and heatwave frequency in the Mediterranean basin and elsewhere in temperate areas may threaten the local persistence of even relatively warm-adapted species

Within-colony segregation of foraging areas: from patterns to processes

Spatial segregation of foraging areas among conspecifics breeding in neighbouring colonies has been observed in several colonial vertebrates and is assumed to originate from competition and information use. Segregation between foraging individuals breeding in different parts of a same colony has comparatively received limited attention, even though it may have strong impacts on colony structure and individual fitness, and thus on population dynamics of colonial species. To shed light on the processes (namely competition and memory) driving small-scale spatial segregation of foraging areas in colonial species, we used empirical data and developed an individual based model (IBM). By GPS tracking lesser kestrels Falco naumanni breeding in an urban area and foraging in the surrounding farmland, we found that foraging areas of individuals nesting in two close-by (ca 600 m) roof terraces (i.e. nest clusters) were significantly spatially segregated. Individuals from different nest clusters showed different departure bearings and encountered different habitats but showed similar fitness traits. Individuals from the same cluster did not seem to follow conspecifics when leaving for a foraging trip. The IBM, based on data from seven roof terraces, showed that such collective spatial segregation does not necessitate social information use: personal information and memory may be sufficient to mechanistically explain intra-colony segregation of foraging areas. Besides, there was a clear distance-dependent segregation: individuals from distant clusters segregated more, matching what is observed at large spatial scales (i.e. among neighbouring colonies). Our results do not question the fact that colonial species may use social information during foraging or that colonies can act as information centres. Instead, they suggest that within-colony foraging range spatial segregation, arising from simple mechanisms not necessarily involving information sharing, might be widespread in colonial systems. These results thus further challenge the long-standing view that colonies should be regarded as single cohesive entities

Experimental nest cooling reveals dramatic effects of heatwaves on reproduction in a Mediterranean bird of prey

Data corresponding to the manuscript GCB-23-0747 titled "Experimental nest cooling reveals dramatic effects of heatwaves on reproduction in a Mediterranean bird of prey