Population differences in the length and early-life dynamics of telomeres among European pied flycatchers.

Telomere length and shortening rate are increasingly being used as biomarkers for long-term costs in ecological and evolutionary studies because of their relationships with survival and fitness. Both early-life conditions and growth, and later-life stressors can create variation in telomere shortening rate. Studies on between-population telomere length and dynamics are scarce, despite the expectation that populations exposed to varying environmental constraints would present divergent telomere length patterns. The pied flycatcher (Ficedula hypoleuca) is a passerine bird breeding across Eurasia (from Spain to western Siberia) and migrating through the Iberian Peninsula to spend the nonbreeding period in sub-Saharan Africa. Thus, different populations show marked differences in migration distance. We studied the large-scale variation of telomere length and early-life dynamics in the pied flycatcher by comparing six European populations across a north-south gradient (Finland, Estonia, England and Spain) predicting a negative effect of migration distance on adult telomere length, and of nestling growth on nestling telomere dynamics. There were clear population differences in telomere length, with English birds from midlatitudes having the longest telomeres. Telomere length did not thus show consistent latitudinal variation and was not linearly linked to differences in migration distance. Early-life telomere shortening rate tended to vary between populations. Fast growth was associated with shorter telomeres in the early life, but faster nestling growth affected telomeres more negatively in northern than southern populations. While the sources of between-population differences in telomere-related biology remain to be more intensively studied, our study illustrates the need to expand telomere studies at the between-population level.

Ecological engineering across a spatial gradient: Sociable weaver colonies facilitate animal associations with increasing environmental harshness.

The spatial distribution of animals in a landscape depends mainly on the distribution of resources. Resource availability is often facilitated by other species and can positively influence local species diversity and affect community structure. Species that significantly change resource availability are often termed ecosystem engineers. Identifying these species is important, but predicting where they have large or small impacts is a key challenge that will enhance the usefulness of the ecosystem engineering concept. In harsh and stressful environments, the stress gradient hypothesis predicts that community structure and function will be increasingly influenced by facilitative interactions. To test this hypothesis, we investigate how the ecosystem engineering role and importance of sociable weavers Philetairus socius varies across a spatial gradient of harshness, for which aridity served as a proxy. These birds build large colonies that are home to hundreds of weavers and host a wide range of avian and non-avian heterospecifics. We investigated the use of weaver colonies on multiple taxa (invertebrates, reptiles, birds and mammals) at multiple sites across a >1,000 km aridity gradient. We show that sociable weaver colonies create localized biodiversity hotspots across their range. Furthermore, trees containing sociable weaver colonies maintained localized animal diversity at sites with lower rainfall, an effect not as pronounced at sites with higher rainfall. Our results were consistent with predictions of the stress gradient hypothesis, and we provide one of the first tests of this hypothesis in terrestrial animal communities. Facilitation and amelioration by ecosystem engineers may mitigate some of the extreme impacts of environmental harshness.

Maternally transferred thyroid hormones and life-history variation in birds.

In vertebrates, thyroid hormones (THs) play an important role in the regulation of growth, development, metabolism, photoperiodic responses and migration. Maternally transferred THs are important for normal early phase embryonic development when embryos are not able to produce endogenous THs. Previous studies have shown that variation in maternal THs within the physiological range can influence offspring phenotype. Given the essential functions of maternal THs in development and metabolism, THs may be a mediator of life-history variation across species. We tested the hypothesis that differences in life histories are associated with differences in maternal TH transfer across species. Using birds as a model, we specifically tested whether maternally transferred yolk THs covary with migratory status, developmental mode and traits related to pace-of-life (e.g. basal metabolic rate, maximum life span). We collected un-incubated eggs (n = 1-21 eggs per species, median = 7) from 34 wild and captive bird species across 17 families and six orders to measure yolk THs [both triiodothyronine (T3) and thyroxine (T4)], compiled life-history trait data from the literature and used Bayesian phylogenetic mixed models to test our hypotheses. Our models indicated that both concentrations and total amounts of the two main forms of THs (T3 and T4) were higher in the eggs of migratory species compared to resident species, and total amounts were higher in the eggs of precocial species, which have longer prenatal developmental periods, than in those of altricial species. However, maternal yolk THs did not show clear associations with pace-of-life-related traits, such as fecundity, basal metabolic rate or maximum life span. We quantified interspecific variation in maternal yolk THs in birds, and our findings suggest higher maternal TH transfer is associated with the precocial mode of development and migratory status. Whether maternal THs represent a part of the mechanism underlying the evolution of precocial development and migration or a consequence of such life histories is currently unclear. We therefore encourage further studies to explore the physiological mechanisms and evolutionary processes underlying these patterns.

Breeding near heterospecifics as a defence against brood parasites: can redstarts lower probability of cuckoo parasitism using neighbours?

Breeding habitat choice based on the attraction to other species can provide valuable social information and protection benefits. In birds, species with overlapping resources can be a cue of good quality habitats; species with shared predators and/or brood parasites can increase joint vigilance or cooperative mobbing, while raptors may provide a protective umbrella against these threats. We tested whether the migratory common redstart (Phoenicurus phoenicurus) is attracted to breed near active nests of the great tit (Parus major), a keystone-information source for migrant passerine birds, or a top predator, the northern goshawk (Accipiter gentilis). This system is unique to test these questions because the redstart is a regular host for the common cuckoo (Cuculus canorus). Therefore, we also evaluated other possible benefits coming from the heterospecific attraction, especially in terms of reducing brood parasitism risk. We monitored redstart occupancy rates, onset of breeding, reproductive investment, and followed nest outcomes in terms of brood parasitism, nest predation risk and overall reproductive success. Redstarts avoided breeding near goshawks, but showed neither attraction nor avoidance to breed next to great tits. Both neighbours neither reduced brood parasitism risk nor affected overall nesting success in redstarts. Redstarts may not use heterospecific attraction for settlement decisions, as associations with other species can only exist when some benefits are gained. Thus, environmental cues may be more important than social information for redstarts when breeding habitat choice. Other front-line defence strategies may have a better impact reducing breeding negative interactions, such brood parasitism.

Ecological engineering across a temporal gradient: Sociable weaver colonies create year-round animal biodiversity hotspots.

Animal distribution in a landscape depends mostly on the availability of resources. This can be facilitated by other species that have positive effects on local species diversity and impact community structure. Species that significantly change resource availability are often termed ecosystem engineers. Identifying these species is key but predicting where they have large or small impacts is an even greater challenge. The stress-gradient hypothesis predicts that the importance of facilitative interactions that shape community structure and function will increase in stressful and harsh environments. In most environments, conditions will fluctuate between harsh and benign periods, yet how the impacts of ecosystem engineers will change in different conditions has received little attention. Monitoring for extended periods will increase the understanding of how engineers may mitigate the extreme differences between changing seasons. We investigated the role of sociable weavers Philetairus socius as ecosystem engineers and examined how the association of species to weaver colonies may vary across a seasonal (temporal) gradient. Sociable weavers build large colonies that are home to hundreds of weaver individuals but also host a wide range of other animal species. We investigated the use of weaver colonies by terrestrial and arboreal vertebrates and birds throughout a calendar year, encompassing harsh and benign periods. We demonstrate that the presence of sociable weaver colonies creates centres of animal activity. Colonies were used by the local Kalahari animal community for foraging, shade, territorial behaviours and roosting sites. Furthermore, animal activity increased with increased primary productivity, but this was not restricted to weaver colonies, suggesting that the importance of colonies does not directionally change across environmental conditions. Our results were not consistent with predictions of the stress-gradient hypothesis across a temporal gradient. We demonstrate the importance of sociable weavers as ecological engineers and the significance of their colonies in structuring the surrounding animal community. Colonies appear to provide a range of different resources for different species. Sociable weaver colonies have large ecological importance to local animal communities and, by mitigating environmental stress, may be increasingly important as human-driven climate change advances.

Pulses of anthropogenic food availability appear to benefit parents, but compromise nestling growth in urban red-winged starlings.

The provision of anthropogenic food undoubtedly influences urban bird fitness. However, the nature of the impact is unclear, with both benefits and costs of urban diets documented. Moreover, the influence of short-term fluctuations in food availability, linked to urban weekday/weekend cycles of human presence, is largely unknown. We explored whether breeding red-winged starlings Onychognathus morio in Cape Town, South Africa, altered foraging and provisioning behaviour between days with high human presence (HHP) and days with low human presence (LHP)-i.e. weekdays versus weekends and vacation days. We investigated the relationship between starling diet, adult body mass and nestling development. Breeding adults consumed and provisioned the same quantity of food, but a significantly greater proportion of anthropogenic food on HHP compared to LHP days. Adults apparently benefited from the anthropogenic diet, experiencing significantly greater mass gain on HHP days. However, nestlings experienced a cost, with the number of HHP days during the nestling period associated negatively with nestling size. Adults may, therefore, benefit from the high calorie content of anthropogenic food, while nestlings may be negatively affected by nutrient limitation. The quantity of food available in urban environments may, therefore, benefit adult survival, while its quality imposes a cost to nestling growth.

Information collected during the post-breeding season guides future breeding decisions in a migratory bird.

Breeding habitat choice and investment decisions are key contributors to fitness in animals. Density of individuals is a well-known cue of habitat quality used for future breeding decisions, but accuracy of density cues decreases as individuals disperse from breeding sites. Used nests remain an available information source also after breeding season, but whether such information is used for breeding decisions is less well known. We experimentally investigated whether migratory, cavity-nesting pied flycatchers (Ficedula hypoleuca) prospect potential breeding sites after breeding season and use old nests as a cue for future breeding decisions. In late summer 2013, forest sites were assigned to four treatments: (1) sites including nest boxes with old nests of heterospecifics (tits), (2) sites including suitable but empty nest boxes, (3) sites with unsuitable nest boxes, or (4) sites without any nest boxes. In the following year, we investigated pied flycatcher habitat choice and reproductive investment according to these "past" cues while also controlling for additional information sources present during settlement. Flycatchers preferred sites where tits had been perceived to breed in the previous year, but only if great tits were also currently breeding in the site and had a relatively high number of eggs. Old flycatchers avoided sites previously treated with suitable but empty cavities, whereas young flycatchers preferred sites where tits had apparently bred in the previous year. Also egg mass, but not clutch size or clutch mass, was affected by the combination of past treatment information and current tit abundance.

Maternal food supplementation and perceived predation risk modify egg composition and eggshell traits but not offspring condition.

Mothers may vary resource allocation to eggs and embryos, which may affect offspring fitness and prepare them for future environmental conditions. The effects of food availability and predation risk on reproduction have been extensively studied, yet their simultaneous impacts on reproductive investment and offspring early life conditions are still unclear. We experimentally manipulated these key environmental elements using a 2×2 full factorial design in wild, free-living pied flycatchers (Ficedula hypoleuca), and measured egg composition, eggshell traits and offspring condition. Eggs laid in food-supplemented nests had larger yolks and thicker shells independently of predation risk, while eggs laid in nests exposed to predator cues had lower levels of immunoglobulins, independent of food supplementation. In nests without predator cues, shell biliverdin content was higher in eggs laid in food-supplemented nests. Incubation was 1 day shorter in food-supplemented nests and shorter incubation periods were associated with higher hatching success, but there were no direct effects of maternal treatment on hatching success. To investigate the impact of maternal treatment (via egg composition) on the offspring, we performed full brood cross-fostering after hatching to unmanipulated nests. Maternal treatment did not significantly affect body mass and immunoglobulin levels of offspring. Our results suggest that although prenatal maternal cues affected egg composition, these egg-mediated effects may not have detectable consequences for offspring growth or immune capacity. Unpredictable environmental stressors may thus affect parental investment in the eggs, but parental care may level off costs and benefits of differential maternal egg allocation.

Interspecific information on predation risk affects nest site choice in a passerine bird.

BACKGROUND: Breeding site choice constitutes an important part of the species niche. Nest predation affects breeding site choice, and has been suggested to drive niche segregation and local coexistence of species. Interspecific social information use may, in turn, result in copying or rejection of heterospecific niche characteristics and thus affect realized niche overlap between species. We tested experimentally whether a migratory bird, the pied flycatcher Ficedula hypoleuca, collects information about nest predation risk from indirect cues of predators visiting nests of heterospecific birds. Furthermore, we investigated whether the migratory birds can associate such information with a specific nest site characteristic and generalize the information to their own nest site choice. RESULTS: Our results demonstrate that flycatchers can use the fate of heterospecific nesting attempts in their own nest site choice, but do so selectively. Young flycatcher females, when making the decision quickly, associated the fate of an artificial nest with nest-site characteristics and avoided the characteristic associated with higher nest predation risk. CONCLUSIONS: Copying nest site choices of successful heterospecifics, and avoiding choices which led to failed attempts, may amplify or counter effects of nest predation on niche overlap, with important consequences for between-species niche divergence-convergence dynamics, species coexistence and predator-prey interactions.

Urban blackbirds have shorter telomeres.

Urbanization, one of the most extreme human-induced environmental changes, represents a major challenge for many organisms. Anthropogenic habitats can have opposing effects on different fitness components, for example, by decreasing starvation risk but also health status. Assessment of the net fitness effect of anthropogenic habitats is therefore difficult. Telomere length is associated with phenotypic quality and mortality rate in many species, and the rate of telomere shortening is considered an integrative measure of the 'life stress' experienced by an individual. This makes telomere length a promising candidate for examining the effects of urbanization on the health status of individuals. We investigated whether telomere length differed between urban and forest-dwelling common blackbirds (Turdus merula). Using the terminal restriction fragment assay, we analysed telomere length in yearlings and older adults from five population dyads (urban versus forest) across Europe. In both age classes, urban blackbirds had significantly shorter telomeres (547 bp) than blackbirds in natural habitats, indicating lower health status in urban blackbirds. We propose several potential hypotheses to explain our results. Our findings show that even successful city dwellers such as blackbirds pay a price for living in these anthropogenic habitats.

Predator encounters have spatially extensive impacts on parental behaviour in a breeding bird community.

Predation risk has negative indirect effects on prey fitness, partly mediated through changes in behaviour. Evidence that individuals gather social information from other members of the population suggests that events in a community may impact the behaviour of distant individuals. However, spatially wide-ranging impacts on individual behaviour caused by a predator encounter elsewhere in a community have not been documented before. We investigated the effect of a predator encounter (hawk model presented at a focal nest) on the parental behaviour of pied flycatchers (Ficedula hypoleuca), both at the focal nest and at nearby nests different distances from the predator encounter. We show that nest visitation of both focal pairs and nearby pairs were affected, up to 3 h and 1 h, respectively. Parents also appeared to compensate initial disrupted feeding by later increasing nest visitation rates. This is the first evidence showing that the behaviour of nearby pairs was affected away from an immediate source of risk. Our results indicate that the impacts of short-term predator encounters may immediately extend spatially to the broader community, affecting the behaviour of distant individuals. Information about predators is probably quickly spread by cues such as intra- and heterospecific alarm calls, in communities of different taxa.

Brood size manipulations in a spatially and temporally varying environment: male Tengmalm's owls pass increased reproductive costs to offspring.

A key tool used to assess reproductive trade-offs in birds is brood size manipulation (BSM) experiments. Most BSM studies have examined the influence on short-term measures of reproductive output. Seldom evaluated are the effects on long-term fitness proxies under temporally or spatially varying environments. Unpredictable environments may affect reproductive trade-offs by altering the value of the brood or hampering optimization of reproductive effort. We reduced or enlarged broods of 140 male Tengmalm's owls Aegolius funereus by one chick during their first lifetime reproductive event. Males differed in age and bred in environments that varied in quality spatially (habitat structure) and temporally (abundance of main food). We measured the short-term (nestling number and condition) and long-term fitness proxies (survival, lifetime fledgling and recruits produced) until all experimental males disappeared from the population. BSMs did not affect fledgling number or condition, but in enlarged broods, offspring condition was lower in territories with a high proportion of agricultural fields. Importantly, no obvious impacts on long-term fitness proxies emerged; lifetime fledgling and recruit production of males did not differ between the BSM treatments. Thus, the primary caregiver (i.e. Tengmalm's owl males) passed increased reproductive costs to their offspring, which is in agreement with other studies investigating intergenerational reproductive trade-offs in species of intermediate lifespan. Reluctance to accept increased current reproductive costs in these systems highlights the potential for sexual conflict in bi-parental care systems in which one of the pair is the primary caregiver.

Informed renesting decisions: the effect of nest predation risk.

Animals should cue on information that predicts reproductive success. After failure of an initial reproductive attempt, decisions on whether or not to initiate a second reproductive attempt may be affected by individual experience and social information. If the prospects of breeding success are poor, long-lived animals in particular should not invest in current reproductive success (CRS) in case it generates costs to future reproductive success (FRS). In birds, predation risk experienced during breeding may provide a cue for renesting success. Species having a high FRS potential should be flexible and take predation risk into account in their renesting decisions. We tested this prediction using breeding data of a long-lived wader, the southern dunlin Calidris alpina schinzii. As predicted, dunlin cued on predation risk information acquired from direct experience of nest failure due to predation and ambient nest predation risk. While the overall renesting rate was low (34.5%), the early season renesting rate was high but declined with season, indicating probable temporal changes in the costs and benefits of renesting. We develop a conceptual cost-benefit model to describe the effects of the phase and the length of breeding season on predation risk responses in renesting. We suggest that species investing in FRS should not continue breeding in short breeding seasons in response to predation risk but without time constraints, their response should be similar to species investing in CRS, e.g. within-season dispersal and increased nest concealment.

Investigating the impacts of artificial light via blackouts.

Natural experiments provide remarkable opportunities to test the large-scale effects of human activities. Widespread energy blackouts offer such an 'experiment' to test the impacts of artificial light at night (ALAN) on wildlife. We use the situation in South Africa, where regular scheduled blackouts are being implemented, to highlight this opportunity.

Urbanization correlates with the prevalence and richness of blood parasites in Eurasian Blackbirds (Turdus merula).

Urbanization is increasing worldwide, producing severe environmental impacts. Biodiversity is affected by the expansion of cities, with many species being unable to cope with the different human-induced stressors present in these landscapes. However, this knowledge is mainly based on research from taxa such as plants or vertebrates, while other organisms like protozoa have been less studied in this context. The impact of urbanization on the transmission of vector-borne pathogens in wildlife is still unclear despite its relevance for animal and human health. Here, we investigated whether cities are associated with changes in the prevalence and richness of lineages of three vector-borne protozoans (Plasmodium, Haemoproteus and Leucocytozoon) in Eurasian blackbirds (Turdus merula) from multiple urban and forest areas in Europe. Our results show important species-specific differences between these two habitat types. We found a significant lower prevalence of Leucocytozoon in urban birds compared to forest birds, but no differences for Plasmodium and Haemoproteus. Furthermore, the richness of parasite lineages in European cities was higher for Plasmodium but lower for Leucocytozoon than in forests. We also found one Plasmodium lineage exclusively from cities while another of Leucocytozoon was only found in forests suggesting a certain level of habitat specialization for these protozoan vectors. Overall, our findings show that cities provide contrasting opportunities for the transmission of different vector-borne pathogens and generate new scenarios for the interactions between hosts, vectors and parasites.

Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide.

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

Higher nest predation risk in association with a top predator: mesopredator attraction?

Breeding close to top predators is a widespread reproductive strategy. Breeding animals may gain indirect benefits if proximity to top predators results in a reduction of predation due to suppression of mesopredators. We tested if passerine birds gain protection from mesopredators by nesting within territories of a top predator, the Ural owl (Strix uralensis). We placed nest boxes for pied flycatchers (Ficedula hypoleuca) in Ural owl nest sites and in control sites (currently unoccupied by owls). The nest boxes were designed so that nest predation risk could be altered (experimentally increased) after flycatcher settlement; we considered predation rate as a proxy of mesopredator abundance. Overall, we found higher nest predation rates in treatment than in control sites. Flycatcher laying date did not differ between sites, but smaller clutches were laid in treatment sites compared to controls, suggesting a response to perceived predation risk. Relative nest predation rate varied between years, being higher in owl nest sites in 2 years but similar in another; this variation might be indirectly influenced by vole abundance. Proximity to Ural owl nests might represent a risky habitat for passerines. High predation rates within owl territories could be because small mesopredators that do not directly threaten owl nests are attracted to owl nest sites. This could be explained if some mesopredators use owl territories to gain protection from their own predators, or if top predators and mesopredators independently seek similar habitats.

Genetic differentiation in an endangered and strongly philopatric, migrant shorebird.

BACKGROUND: Populations living in fragmented habitats may suffer from loss of genetic variation and reduced between-patch dispersal, which are processes that can result in genetic differentiation. This occurs frequently in species with reduced mobility, whereas genetic differentiation is less common among mobile species such as migratory birds. The high dispersal capacity in the latter species usually allows for gene flow even in fragmented landscapes. However, strongly philopatric behaviour can reinforce relative isolation and the degree of genetic differentiation. The Southern Dunlin (Calidris alpina schinzii) is a philopatric, long-distance migratory shorebird and shows reduced dispersal between isolated breeding patches. The endangered population of the Southern Dunlin breeding at the Baltic Sea has suffered from habitat deterioration and fragmentation of coastal meadows. We sampled DNA across the entire population and used 12 polymorphic microsatellite loci to examine whether the environmental changes have resulted in genetic structuring and loss of variation. RESULTS: We found a pattern of isolation-by-distance across the whole Baltic population and genetic differentiation between local populations, even within the southern Baltic. Observed heterozygosity was lower than expected throughout the range and internal relatedness values were positive indicating inbreeding. CONCLUSIONS: Our results provide long-term, empirical evidence for the theoretically expected links between habitat fragmentation, population subdivision, and gene flow. They also demonstrate a rare case of genetic differentiation between populations of a long-distance migratory species. The Baltic Southern Dunlin differs from many related shorebird species that show near panmixia, reflecting its philopatric life history and the reduced connectivity of its breeding patches. The results have important implications as they suggest that reduced connectivity of breeding habitats can threaten even long-distance migrants if they show strong philopatry during breeding. The Baltic Southern Dunlin warrants urgent conservation efforts that increase functional connectivity and gene flow between breeding areas.

Predator proximity as a stressor in breeding flycatchers: mass loss, stress protein induction, and elevated provisioning.

We investigated the physiological and behavioral consequences for prey breeding at different distances from a nesting predator. In a natural setting, Pied Flycatchers (Ficedula hypoleuca) made territory location decisions relative to established Sparrowhawk (Accipiter nisus) nests. From female flycatchers attending nests at different distances from Sparrowhawk nests, we measured body mass, blood stress protein (HSP60 and HSP70), and plasma immunoglobulin levels at the beginning (initial) and end (final) of the flycatcher breeding cycle, and provisioning rates during the nestling phase. We found that individuals breeding in closer proximity to Sparrowhawk nests, under higher perceived predation risk, showed significantly lower body mass, higher stress protein and immunoglobulin levels, and higher nestling provisioning rates compared to those individuals breeding farther away. Across the range of distances investigated (30-610 m), final stress protein levels decreased linearly with distance, whereas the final measures of the other variables showed unimodal trends, increasing or decreasing until an intermediate distance (approximately 350 m) and reversing the direction of the trend. Within 300 m, however, all measures showed significant linear associations with distance from the Sparrowhawk nest. Body mass and stress protein associations with distance from Sparrowhawk nests were only present during late breeding, and not in early incubation. Spatial proximity to Sparrowhawk nests consistently explained significant variation in both physiological and behavioral measures, despite the multitude of potential sources of variation for these measures in a natural setting. This suggests that predictable spatial patterns in these measures in avian communities are determined by the sites of breeding predators. Habitat selection decisions of migrant prey that vary only slightly spatially have consequences even at the cellular level, which plausibly have impacts on individual survival. In addition, this study suggests that predation risk is an important factor affecting physiological condition of prey, including stress protein induction in terrestrial vertebrates.

Habitat selection as an antipredator behaviour in a multi-predator landscape: all enemies are not equal.

1. Breeding territory choice constitutes a crucial antipredator behaviour for animals that determines reproductive success and survival during the breeding season. On arrival to breeding grounds migrant prey face a multitude of 'waiting' predators already settled within the landscape. 2. We studied territory selection and reproductive investment of migrant pied flycatcher (Ficedula hypoleuca) relative to breeding pygmy owls (POs) (Glaucidium passerinum) and Tengmalm's owls (TOs) (Aegolius funereus). Diurnal POs present a greater predation threat to adult flycatchers (up to 80% songbirds in diet) compared with nocturnal TOs (up to 36%). 3. During territory selection, pied flycatchers strongly avoided POs (occupation: 42% in presence vs. 92% in absence of owl nest) but not TOs (80% vs. 75%). This suggests that flycatchers are able to distinguish between two potential predators, avoiding dangerous POs but not obviously responding to the less risky TOs. 4. Flycatchers responded to presence of PO nests with c. 4-day delay in the start of egg-laying. A significantly prolonged nest building period contributed to this potentially costly breeding delay. Flycatchers further significantly reduced initial reproductive investment in presence of POs by laying 8.2% smaller clutch sizes, even if laying date was controlled. No breeding delay and clutch size reduction was found relative to TO presence. 5. Our results highlight flexibility in breeding territory selection and reproductive strategies as antipredator responses to perceived risk in a multi-predator environment. This supports the idea that for prey, not all predators are equal.