Adult body mass is heritable, positively genetically correlated and under selection of differing shapes between the sexes in a bird with little apparent sexual dimorphism.

In most animals, body mass varies with ecological conditions and is expected to reflect how much energy can be allocated to reproduction and survival. Because the sexes often differ in their resource acquisition and allocation strategies, variations in adult body mass and their consequences on fitness can differ between the sexes. Assessing the relative contributions of environmental and genetic effects (i.e. heritability)-and whether these effects and their fitness consequences are sex-specific-is essential to gain insights into the evolution of sexual dimorphism and sexual conflicts. We used 20+ years of data to study the sources of variation in adult body mass and associated fitness consequences in a bird with biparental care, the Alpine swift (Tachymarptis melba). Swifts appear monomorphic to human observers, though subtle dimorphisms are present. We first investigated the effects of weather conditions on adult body mass using a sliding window analysis approach. We report a positive effect of temperature and a negative effect of rainfall on adult body mass, as expected for an aerial insectivorous bird. We then quantified the additive genetic variance and heritability of body mass in both sexes and assessed the importance of genetic constraints on mass evolution by estimating the cross-sex genetic correlation. Heritability was different from zero in both sexes at ~0.30. The positive cross-sex genetic correlation and comparable additive genetic variance between the sexes suggest the possibility for evolutionary constraints when it comes to body mass. Finally, we assessed the sex-specific selection on adjusted body mass using multiple fitness components. We report directional positive and negative selection trending towards stabilizing and diversifying selection on females and males respectively in relation to the weighted proportion of surviving fledglings. Overall, these results suggest that while body mass may be able to respond to environmental conditions and evolve, genetic constraints would result in similar changes in both sexes or an overall absence of response to selection. It remains unclear whether the weak (1%) dimorphism in Alpine swift body mass we report is simply a result of the similar fitness peaks between the sexes or of genetic constraints.

Molecular investigation on infection by haemosporidians in three Western Palearctic species of swift (Apodidae) and their ectoparasitic louse flies.

Swifts (Apodidae) are an unusual group of birds that spend most of their lives in flight, landing only when breeding. Although this aerial lifestyle greatly reduces their likelihood of being bitten by vectors and infected by vector-born parasites, swifts can still be heavily infested during breeding by nest-based vectors such as louse flies (Hippoboscidae). Here, we investigated host, vector, and vector-borne parasite relationships in the three most widespread swift species in the Western Palearctic (WP): common swifts (Apus apus), pallid swifts (A. pallidus), and alpine swifts (Tachymarptis melba), their nest-based louse flies (Crataerina pallida and C. melbae) and avian haemosporidians (genera Haemoproteus, Plasmodium, and Leucocytozoon). Studies of haemosporidian infections in Apodidae remain limited, with clear evidence of infection found to date in just four Neotropical and one Australasian species. The possible role of louse flies in transmitting haemosporidian infections has never been tested in swifts. We assessed the occurrence of haemosporidian infection by PCR screenings of DNA from blood samples from 34 common swifts and 44 pallid swifts from Italy, and 45 alpine swifts from Switzerland. We also screened 20 ectoparasitic louse flies present on 20 birds and identified them by both morphological features and cytochrome oxidase subunit 1 (COI) barcodes. Our results provide no evidence of haemosporidian infection in the 123 swifts tested or in the two louse fly species we identified. Our findings are consistent with available knowledge showing no haemosporidian occurrence in WP swift species and that the most likely infection route for these highly aerial species (via louse fly ectoparasites during nesting) is unlikely.

Estimating the long-term repeatability of food-hoarding behaviours in an avian predator.

Food-hoarding behaviour is widespread in the animal kingdom and enables predictable access to food resources in unpredictable environments. Within species, consistent variation among individuals in food-hoarding behaviours may indicate the existence of individual strategies, as it likely captures intrinsic differences in how individuals cope with risks (e.g. starvation, pilferage). Using 17 years of data, we estimated the long-term repeatability of 10 food-hoarding behaviours in a population of Eurasian pygmy owls (Glaucidium passerinum), a small avian predator subject to high temporal fluctuations in its main prey abundance. We found low repeatability in the proportion of shrews and the average prey mass stored for both sexes, while females were moderately repeatable in the mass and the number of prey items stored. These two pairs of behaviours were tightly correlated among individuals and might represent two different sets of individual strategies to buffer against starvation risks.

Climate change and perishable food hoards of an avian predator: Is the freezer still working?

Changing climate can modify predator-prey interactions and induce declines or local extinctions of species due to reductions in food availability. Species hoarding perishable food for overwinter survival, like predators, are predicted to be particularly susceptible to increasing temperatures. We analysed the influence of autumn and winter weather, and abundance of main prey (voles), on the food-hoarding behaviour of a generalist predator, the Eurasian pygmy owl (Glaucidium passerinum), across 16 years in Finland. Fewer freeze-thaw events in early autumn delayed the initiation of food hoarding. Pygmy owls consumed more hoarded food with more frequent freeze-thaw events and deeper snow cover in autumn and in winter, and lower precipitation in winter. In autumn, the rotting of food hoards increased with precipitation. Hoards already present in early autumn were much more likely to rot than the ones initiated in late autumn. Rotten food hoards were used more in years of low food abundance than in years of high food abundance. Having rotten food hoards in autumn resulted in a lower future recapture probability of female owls. These results indicate that pygmy owls might be partly able to adapt to climate change by delaying food hoarding, but changes in the snow cover, precipitation and frequency of freeze-thaw events might impair their foraging and ultimately decrease local overwinter survival. Long-term trends and future predictions, therefore, suggest that impacts of climate change on wintering food-hoarding species could be substantial, because their 'freezers' may no longer work properly. Altered usability and poorer quality of hoarded food may further modify the foraging needs of food-hoarding predators and thus their overall predation pressure on prey species. This raises concerns about the impacts of climate change on boreal food webs, in which ecological interactions have evolved under cold winter conditions.

Age and sex differences in numerical responses, dietary shifts, and total responses of a generalist predator to population dynamics of main prey.

Fluctuations in the abundance of main prey species might shape animal communities, by inducing numerical responses and dietary shifts in predators. Whether numerical responses and dietary shifts differ among individuals of different age and sex has so far gained little attention. These differences could affect how much predators consume main and alternative prey, thus causing variation in predation pressure on main and alternative prey species. We studied the effect of fluctuating main prey abundance (voles) in autumn on the age and sex composition of a food-hoarding population of Eurasian pygmy owls Glaucidium passerinum (327 individuals), and on the species composition of their food stores in western Finland during 2003-2017 (629 food stores). Numbers of yearlings (< 1-year old) of both sexes and adult (+ 1-year old) females increased with increasing vole abundance. During low vole abundance, adult owls stored more small birds and less small mammals than yearlings. Females stored more small mammals than males and showed a tendency to store less birds. The amount of consumed birds (the most important alternative prey), and in particular of crested, willow, great, and blue tits, increased with low vole densities. Our results show that numerical, functional, and total responses of pygmy owls, and probably also other vertebrate predators, to the availability of the main prey in winter are shaped by the age and sex composition of the predator population, which both show large spatio-temporal variation in boreal forests.

Trait-specific sensitive developmental windows: Wing growth best integrates weather conditions encountered throughout the development of nestling Alpine swifts.

The size and growth patterns of nestling birds are key determinants of their survival up to fledging and long-term fitness. However, because traits such as feathers, skeleton and body mass can follow different developmental trajectories, our understanding of the impact of adverse weather on development requires insights into trait-specific sensitive developmental windows. We analysed data from nestling Alpine swifts in Switzerland measured throughout growth up to the age of 50 days (i.e. fledging between 50 and 70 days), for wing length and body mass (2693 nestlings in 25 years) and sternum length (2447 nestlings in 22 years). We show that the sensitive developmental windows for wing and sternum length corresponded to the periods of trait-specific peak growth, which span almost the whole developmental period for wings and the first half for the sternum. Adverse weather conditions during these periods slowed down growth and reduced size. Although nestling body mass at 50 days showed the greatest inter-individual variation, this was explained by weather in the two days before measurement rather than during peak growth. Interestingly, the relationship between temperature and body mass was not linear, and the initial sharp increase in body mass associated with the increase in temperature was followed by a moderate drop on hot days, likely linked to heat stress. Nestlings experiencing adverse weather conditions during wing growth had lower survival rates up to fledging and fledged at later ages, presumably to compensate for slower wing growth. Overall, our results suggest that measures of feather growth and, to some extent, skeletal growth best capture the consequences of adverse weather conditions throughout the whole development of offspring, while body mass better reflects the short, instantaneous effects of weather conditions on their body reserves (i.e. energy depletion vs. storage in unfavourable vs. favourable conditions).

Shrinking Alpine chamois: higher spring temperatures over the last 27 years in Switzerland are linked to a 3 kg reduction in body mass of yearlings.

Although climate change is considered to be partly responsible for the size change observed in numerous species, the relevance of this hypothesis for ungulates remains debated. We used body mass measurements of 5635 yearlings (i.e. 1.5 years old) of Alpine chamois (Rupicapra rupicapra) harvested in September in the Swiss Alps (Ticino canton) from 1992 to 2018. In our study area, during this period, yearlings shrank by ca 3 kg while temperatures between May and July rose by 1.7°C. We identified that warmer temperatures during birth and the early suckling period (9 May to 2 July in the year of birth) had the strongest impact on yearling mass. Further analyses of year-detrended mass and temperature data indicate that this result was not simply due to changes in both variables over years, but that increases in temperature during this particularly sensitive time window for development and growth are responsible for the decrease in body mass of yearling chamois. Altogether, our results suggest that rising temperatures in the Alpine regions could significantly affect the ecology and evolution of this wild ungulate.

The hidden cost of following currents: Microplastic ingestion in a planktivorous seabird.

Microplastics are increasingly pervasive pollutants, particularly abundant in the neuston where they drift with currents. We assessed dietary microplastic ingestion in the Mediterranean storm petrel (Hydrobates pelagicus melitensis), a small pelagic seabird that forages on plankton and inhabit the Mediterranean sea, one of the most polluted seas worldwide. We collected spontaneous regurgitates from 30 chick-rearing individuals and used GPS tracking data from 7 additional individuals to locate foraging areas. Birds foraged in pelagic areas characterized by water stirring and mixing, and regurgitates from 14 individuals (i.e. 45 %) contained microplastics. Fibers were the dominant shape (56 %), with polyester, polyethylene and nylon being the most frequent polymers. Our findings highlight the potential sensitivity of this species of conservation interest to plastic pollution and suggest that storm petrel regurgitates can be a valuable matrix to investigate microplastic ingestion in planktonic foragers, providing a characterization of spatio-temporal patterns of microplastic exposure in pelagic environments.