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Owls (Strigiformes) evolved specific adaptations to their nocturnal predatory lifestyle, such as asymmetrical ears, a facial disc, and a feather structure allowing silent flight. Owls also share some traits with diurnal raptors and other nocturnal birds, such as cryptic plumage patterns, reversed sexual size dimorphism and acute vision and hearing. The genetic basis of some of these adaptations to a nocturnal predatory lifestyle has been studied by candidate gene approaches, but rarely with genome-wide scans. Here, we used a genome-wide comparative analysis to test for selection in the early history of the owls. We estimated the substitution rates in the coding regions of twenty bird genomes, including eleven owls of which five were newly sequenced. Then, we tested for functional overrepresentation across the genes that showed signals of selection. In the ancestral branch of the owls, we found traces of positive selection in the evolution of genes functionally related to visual perception, especially to phototransduction, and to chromosome packaging. Several genes that have been previously linked to acoustic perception, circadian rhythm and feather structure also showed signals of an accelerated evolution in the origin of the owls. We discuss the functions of the genes under positive selection and their putative association with the adaptation to the nocturnal predatory lifestyle of the owls.

Age‐specific variation in reproductive effort can affect population dynamics, and is a key component of the evolution of reproductive tactics. Late‐life declines are a typical feature of variation in reproduction. However, the cause of these declines, and thus their implications for the evolution of life‐history tactics, may differ. Some prior studies have shown late‐life reproductive declines to be tied to chronological age, whereas other studies have found declines associated with terminal reproduction irrespective of chronological age. We investigated the extent to which declines in late life reproduction are related to chronological age, terminal reproductive attempt or a combination of both in the thorn‐tailed rayadito Aphrastura spinicauda, a small passerine bird that inhabits the temperate forest of South America. To this end we used long‐term data (10 years) obtained on reproductive success (laying date, clutch size and nestling weight) of females in a Chilean population. Neither chronological age nor terminal reproductive attempt explained variation in clutch size or nestling weight, however we observed that during the terminal reproductive attempt older females tended to lay later in the breeding season and younger females laid early in the breeding season, but this was not the case when the reproductive attempt was not the last. These results suggests that both age‐dependent and age‐independent effects influence reproductive output and therefore that the combined effects of age and physiological condition may be more relevant than previously thought.

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Within‐population variation in timing of breeding may be linked to a trade‐off between the risks and benefits of breeding earlier. This trade‐off may be mediated by individual risk‐taking behaviour, but this needs to be assessed in detail in wild populations. Here, we recorded timing of breeding and risk‐taking behaviour during three consecutive breeding seasons in a resident population of Thorn‐tailed Rayadito Aphrastura spinicauda located in Navarino Island (55°S), southern Chile. Navarino is a high‐latitude, highly seasonal continental island in southern Chile where early breeding may be risky for rayaditos, given the presence of low temperatures, storms and relatively low food abundance during early spring. We used novel environment tests to assess exploratory behaviour, which in turn was used as a proxy of risk‐taking behaviour. In addition, we evaluated the potential consequences of timing of breeding and risk‐taking behaviour on three measures of reproductive success: clutch size, number of fledglings produced and body condition of the offspring. We found that risk‐prone individuals started breeding earlier than risk‐averse individuals but we did not find evidence for an effect of timing of breeding on any of the variables of seasonal breeding success. However, we observed that fast‐exploring females tended to lay smaller clutches. Measurements reflecting lifetime reproductive success may better reflect an effect of timing of breeding and risk‐taking behaviour, but this needs to be studied. Our results support the idea that risk‐taking behaviour is linked to early breeding in high‐latitude environments. We suggest that, despite the risks that low temperatures and snowstorms pose to breeding rayaditos during early spring, it is possible that early breeders increase the probability of occupying better nesting cavities and they may adjust the timing of breeding to match brood provisioning with peak resource abundance.

Life-history theory predicts that hosts may adjust the costs of parasites by altering their reproductive effort. Haemosporidian parasites can affect the reproductive output of wild birds in multiple ways. Thorn-tailed Rayaditos Aphrastura spinicauda breeding in Navarino Island, southern Chile (55°-40°S), experience a high prevalence of the haemosporidian Leucocytozoon spp., which opens the possibility of exploring how these parasites may affect reproductive output in a Neotropical bird species. We compared several variables describing reproductive output (laying date, clutch size, incubation period, brood size, nestling body condition and early-life telomere length) of infected and non-infected parents (individually and as breeding pairs). We found that infected females and breeding pairs with both parents infected showed significantly shorter incubation periods than uninfected Thorn-tailed Rayaditos. Furthermore, breeding pairs where both parents were infected raised nestlings with higher body condition than nestlings for which infection was present in only one or in neither of the parents. Our results suggest that the higher the parental investment, the higher the risk of relapse of chronic infection by Leucocytozoon spp. Thorn-tailed Rayaditos that decrease their incubation period pay the cost of infection to take advantage of early breeding through a greater availability of resources, producing nestlings with higher body condition.

Understanding the targets of selection associated with changes in behavioral traits represents an important challenge of current evolutionary research. Owls (Strigiformes) are a diverse group of birds, most of which are considered nocturnal raptors. However, a few owl species independently adopted a diurnal lifestyle in their recent evolutionary history. We searched for signals of accelerated rates of evolution associated with a diurnal lifestyle using a genome-wide comparative approach. We estimated substitution rates in coding and non-coding conserved regions of the genome of seven owl species, including three diurnal species. Substitution rates of the non-coding elements were more accelerated than those of protein-coding genes. We identified new, owl-specific conserved non-coding elements as candidates of parallel evolution during the emergence of diurnality in owls. Our results shed light on the molecular basis of adaptation to a new niche and highlight the importance of regulatory elements for evolutionary changes in behavior. These elements were often involved in the neuronal development of the brain.

Extra-pair behavior is present in ~76% of all socially monogamous birds with biparental care whose genetic mating system has been described through molecular methods (Brouwer & Griffith, 2019). This behavior consists of males and females copulating with individuals other than their social partner, and as a consequence, broods of socially monogamous pairs may have several genetic fathers (Kempenaers & Schlicht, 2010).From extra-pair behavior, males can obtain a direct benefit on fitness by increasing the number of sired offspring, while females may obtain indirect benefits by increasing offspring genetic quality (good genes hypothesis, see Hamilton & Zuk, 1982; genetic compatibility hypothesis, see Mitton et al., 1993;Brown, 1997). Additionally, it is possible that unfaithful females reduce the risk of clutch failure in case their social partner is infertile (Kempenaers & Schlicht, 2010;Santema et al., 2020). Nevertheless, given that males do not provide resources for the extra-pair female and their offspring, extra-pair behavior may have some costs that are yet unclear. For instance, in House sparrows (Passer domesticus), extra-pair offspring show lower probability of