Simultaneous GPS-tracking of parents reveals a similar parental investment within pairs, but no immediate co-adjustment on a trip-to-trip basis

Prospecting movements link phenotypic traits to female annual potential fitness in a nocturnal predator

Recent biologging technology reveals hidden life and breeding strategies of nocturnal animals. Combining animal movement patterns with individual characteristics and landscape features can uncover meaningful behaviours that directly influence fitness. Consequently, defining the proximate mechanisms and adaptive value of the identified behaviours is of paramount importance. Breeding female barn owls (Tyto alba), a colour-polymorphic species, recurrently visit other nest boxes at night. We described and quantified this behaviour for the first time, linking it with possible drivers, and individual fitness. We GPS-equipped 178 female barn owls and 122 male partners from 2016 to 2020 in western Switzerland during the chick rearing phase. We observed that 111 (65%) of the tracked breeding females were (re)visiting nest boxes while still carrying out their first brood. We modelled their prospecting parameters as a function of brood-, individual- and partner-related variables and found that female feather eumelanism predicted the emergence of prospecting behaviour (less melanic females are usually prospecting). More importantly we found that increasing male parental investment (e.g., feeding rate) increased female prospecting efforts. Ultimately, females would (re)visit a nest more often if they had used it in the past and were more likely to lay a second clutch afterwards, consequently having higher annual fecundity than non-prospecting females. Despite these apparent immediate benefits, they did not fledge more chicks. Through biologging and long-term field monitoring, we highlight how phenotypic traits (melanism and parental investment) can be related to movement patterns and the annual potential reproductive output (fecundity) of female barn owls.

Active breeding seabirds prospect alternative breeding colonies

Compared to other animal movements, prospecting by adult individuals for a future breeding site is commonly overlooked. Prospecting influences the decision of where to breed and has consequences on fitness and lifetime reproductive success. By analysing movements of 31 satellite- and GPS-tracked gull and tern populations belonging to 14 species in Europe and North America, we examined the occurrence and factors explaining prospecting by actively breeding birds. Prospecting in active breeders occurred in 85.7% of studied species, across 61.3% of sampled populations. Prospecting was more common in populations with frequent inter-annual changes of breeding sites and among females. These results contradict theoretical models which predict that prospecting is expected to evolve in relatively predictable and stable environments. More long-term tracking studies are needed to identify factors affecting patterns of prospecting in different environments and understand the consequences of prospecting on fitness at the individual and population level.

Energetic and behavioral consequences of migration: an empirical evaluation in the context of the full annual cycle

Seasonal migrations are used by diverse animal taxa, yet the costs and benefits of migrating have rarely been empirically examined. The aim of this study was to determine how migration influences two ecological currencies, energy expenditure and time allocated towards different behaviors, in a full annual cycle context. We compare these currencies among lesser black-backed gulls that range from short- (< 250 km) to long-distance (> 4500 km) migrants. Daily time-activity budgets were reconstructed from tri-axial acceleration and GPS, which, in conjunction with a bioenergetics model to estimate thermoregulatory costs, enabled us to estimate daily energy expenditure throughout the year. We found that migration strategy had no effect on annual energy expenditure, however, energy expenditure through time deviated more from the annual average as migration distance increased. Patterns in time-activity budgets were similar across strategies, suggesting migration strategy does not limit behavioral adjustments required for other annual cycle stages (breeding, molt, wintering). Variation among individuals using the same strategy was high, suggesting that daily behavioral decisions (e.g. foraging strategy) contribute more towards energy expenditure than an individual's migration strategy. These findings provide unprecedented new understanding regarding the relative importance of fine versus broad-scale behavioral strategies towards annual energy expenditures.

Songbird parents coordinate offspring provisioning at fine spatio-temporal scales

For parents, rearing offspring together is far from a purely cooperative exercise, as a conflict of interest (‘sexual conflict’) exists over their optimum level of care. Recent theory emphasizes that sexual conflict can be evolutionarily resolved, and complete parental cooperation can occur, if parents directly respond (‘negotiate’) to each other and coordinate their level of care. Despite numerous experiments showing that parents are responsive to each other, we still lack empirical evidence of the behavioural mechanisms by which this negotiation occurs.

In this study, we investigated the spatio‐temporal coordination of parental provisioning behaviour as a possible mechanism of negotiation over parental care.

We deployed an automated radiotracking technology to track the provisioning activity of wild great tit Parus major pairs during chick rearing. Our analyses represent the first detailed spatial and temporal description of foraging coordination in songbird parents in a natural context.

We demonstrate that the foraging behaviour of the two parents is highly coordinated in space and time, with parents changing their foraging locations in conjunction with their partners' movements.

Therefore, foraging coordination could be a mechanism by which parents directly monitor and respond to each other's level of investment.