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°C higher than in shaded ones during heatwaves, that is, spells of extreme air temperature (>37°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°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.

Monitoring Colonies of Large Gulls Using UAVs: From Individuals to Breeding Pairs.

Measuring success or failure in the conservation of seabirds depends on reliable long-term monitoring. Traditionally, this monitoring has been based on line transects and total or point counts, all of which are sensitive to subjective interpretation. Such methods have proven to consistently record fewer individuals than intensive efforts, while requiring many hours of fieldwork and resulting in high disturbance. New technologies, such as drones, are potentially useful monitoring tools, as they can cover large areas in a short time, while providing high-resolution data about bird numbers and status. This study conducted two types of Uncrewed Aerial Vehicle (UAV) surveys in a big colony of multispecies breeding gulls. From a 25 m height, we photographed 30 circle plots where nests were also counted on the ground, showing that the number of occupied nests/breeding pairs could be estimated accurately by multiplying the number of counted individuals with a 0.7 conversion factor. A fixed-wing UAV was used to photograph the entire island to compare drone counts with counts conducted by traditional methods, were we counted a higher number of breeding pairs than the traditional count (1.7-2.2 times more individuals). It was concluded that UAVs provided improved estimates of colony size with much reduced monitoring effort.

The effect of nest temperature on growth and survival in juvenile Great Tits Parus major.

For birds, maintaining an optimal nest temperature is critical for early-life growth and development. Temperatures deviating from this optimum can affect nestling growth and fledging success with potential consequences on survival and lifetime reproductive success. It is therefore particularly important to understand these effects in relation to projected temperature changes associated with climate change.Targets set by the 2015 Paris Agreement aim to limit temperature increases to 2°C, and, with this in mind, we carried out an experiment in 2017 and 2018 where we applied a treatment that increased Great Tit Parus major nest temperature by approximately this magnitude (achieving an increase of 1.6°C, relative to the control) during the period from hatching to fledging to estimate how small temperature differences might affect nestling body size and weight at fledging and fledging success.We recorded hatching and fledging success and measured skeletal size (tarsus length) and body mass at days 5, 7, 10, and 15 posthatch in nestlings from two groups of nest boxes: control and heated (+1.6°C).Our results show that nestlings in heated nest boxes were 1.6% smaller in skeletal size at fledging than those in the cooler control nests, indicating lower growth rates in heated boxes, and that their weight was, in addition, 3.3% lower.These results suggest that even fairly small changes in temperature can influence phenotype and postfledging survival in cavity-nesting birds. This has the potential to affect the population dynamics of these birds in the face of ongoing climatic change, as individuals of reduced size in colder winters may suffer from decreased fitness.

Problem-solving in a cooperative task in peach-fronted conures (Eupsittula aurea).

Cooperation is a complex behaviour found in many kinds of organisms and occurs between individuals of the same and different species. Several studies have examined the intentionality of this behaviour by testing the animals' understanding of the need for a partner when working in pairs. The mammalian species tested express such understanding, whereas most tested birds fail, especially when the test involves a delayed access to the setup by one of the co-operators. In the present study, the cooperative problem-solving capability of four peach-fronted conures (Eupsittula aurea) was investigated with the loose string test. All four parrots solved the paradigm by simultaneously pulling the ends of the same string to bring a platform with a food reward within reach. They were also capable of solving the task when one of the co-operators was delayed, even when visually isolated from each other. To further test their comprehension and to exclude the birds relying on task-associated cues, we video-recorded the trials and quantified possible cues and strategies for timing the pulling behaviour (e.g., sound of the partner's door when opening, sound of steps of partner approaching). The preferred cue to start pulling was to wait for their partner's arrival to the string. The number of vocalisations was significantly higher during visually isolated conditions and for successful trials compared to failed trials, suggesting possible information exchange. Our findings show that peach-fronted conures can solve a cooperative task, and that cooperation success is not determined by external cues or by partner identity or affinity.