Roost site selection by Little Owls Athene noctua in relation to environmental conditions and life‐history stages

Roost site selection is a state‐dependent process, affected by the individual's costs and benefits of roosting at a specific site in the available environment. Costs and benefits of different roost sites vary in relation to intrinsic factors and environmental conditions. Thus, the cost–benefit functions of roost sites are expected to differ between seasons and life‐history stages, resulting in adjustments in roost site selection. Studying roost site selection throughout the year therefore provides information about year‐round habitat requirements at different life‐history stages. However, little is known about the roosting behaviour of birds. Here, the roost site selection of Little Owls Athene noctua was studied by repeated daytime location of 24 adult and 75 juvenile radiotagged individuals from July to November. Little Owls preferred sheltered roost sites such as tree cavities with multiple entrances. They increasingly used sheltered sites from summer to winter and preferentially used sheltered roost sites with low ambient temperatures. Juveniles used significantly less sheltered sites during dispersal than before and afterwards, and used less sheltered sites than adults within their home‐range. The survival probability of birds roosting frequently at exposed sites was reduced. Roost site selection is probably driven by the two mechanisms of predator avoidance and thermoregulation, and the costs of natal dispersal may include increased predation threat and higher energy expenditure for thermoregulation. We suggest that adequate roost sites, such as multi‐entrance tree cavities, are an important habitat requirement for Little Owls and that habitat quality can be affected by manipulating their availability.     

Post‐fledging survival of Little Owls Athene noctua in relation to nestling food supply

Among the range of determinants of post‐fledging survival in altricial birds, the energy supply to the growing juveniles is likely to play a central role. However, the exact mechanisms shaping post‐fledging survival are poorly understood. Using a food supplementation experiment, we determined the effect of variation in food supply on the survival of juvenile Little Owls Athene noctua from hatching to 2 months post‐fledging. Experimental broods were food‐supplemented for 36 days during the nestling and the early post‐fledging period. The fate of 307 juveniles (95 of them provided with extra food) was determined by nest monitoring and radiotelemetry. In unsupplemented birds, the rates of survival measured at 5‐day intervals were lowest during the nestling stage, remained low during the early post‐fledging stage and steadily increased after about 2 weeks post‐fledging. Food supplementation substantially increased nestling survival, but we detected no direct treatment effect on post‐fledging survival. Instead, we found a strong indirect effect of food supplementation, in that fledglings of good physical condition had markedly higher chances of surviving the post‐fledging period compared with those in poor condition. Experimental food supplementation increased survival over the first 3 months from 45% to 64.6%. This suggests that energy reserves built up during the nestling stage influence post‐fledging survival and ultimately parental reproductive output. The low nestling and post‐fledging survival shows that the early life‐history stages constitute a crucial bottleneck of reproductive ecology in Little Owls. The strong treatment effects on the number of independent offspring indicate that natural variation in food supply is an important determinant of spatio‐temporal patterns in Little Owl demography.     

Foraging behaviour of Magellanic Penguins during the early chick‐rearing period at Isla de los Estados,Argentina

Studies of the at‐sea distribution and trophic ecology of penguins are essential to understand their role in the broader marine food web. Magellanic Penguins Spheniscus magellanicus have a wide distribution and their foraging behaviour varies across breeding sites and between sexes, among others. In this study, we characterized the at‐sea areas, the diving strategies and the relative trophic level of Magellanic Penguins breeding at Isla de los Estados, Argentina, during the early chick‐rearing period. In addition, we quantified the interannual, sexual and individual variability in those parameters during three breeding seasons (2011–2013) using devices recording position and dive depth, and obtained blood samples for stable isotope analysis. During the early chick‐rearing period, Magellanic Penguins showed small differences between the sexes in their foraging behaviour and large overlap in the at‐sea areas used, suggesting no intraspecific variation between sexes. Although there was interannual variability in the foraging behaviour and the trophic level of the penguins, most of the studied nests managed successfully to raise both chicks during the first stage of the breeding cycle (guard stage). The foraging ecology of Magellanic Penguins from this colony was comparable with results of past studies at other breeding colonies. This study contributes to the identification of important at‐sea areas for Magellanic Penguins at the southern edge of their distribution and also to the identification of possible threats in the study area such as interaction with fisheries.     

Using population viability analysis,genomics, and habitat suitability to forecast future population patterns of Little Owl Athene noctua across Europe

The agricultural scene has changed over the past decades, resulting in a declining population trend in many species. It is therefore important to determine the factors that the individual species depend on in order to understand their decline. The landscape changes have also resulted in habitat fragmentation, turning once continuous populations into metapopulations. It is thus increasingly important to estimate both the number of individuals it takes to create a genetically viable population and the population trend. Here, population viability analysis and habitat suitability modeling were used to estimate population viability and future prospects across Europe of the Little Owl Athene noctua, a widespread species associated with agricultural landscapes. The results show a high risk of population declines over the coming 100 years, especially toward the north of Europe, whereas populations toward the southeastern part of Europe have a greater probability of persistence. In order to be considered genetically viable, individual populations must count 1,000–30,000 individuals. As Little Owl populations of several countries count <30,000, and many isolated populations in northern Europe count <1,000 individuals, management actions resulting in exchange of individuals between populations or even countries are probably necessary to prevent losing <1% genetic diversity over a 100‐year period. At a continental scale, a habitat suitability analysis suggested Little Owl to be affected positively by increasing temperatures and urban areas, whereas an increased tree cover, an increasing annual rainfall, grassland, and sparsely vegetated areas affect the presence of the owl negatively. However, the low predictive power of the habitat suitability model suggests that habitat suitability might be better explained at a smaller scale.     

Relationships between survival and habitat suitability of semi‐aquatic mammals

Spatial distribution and habitat selection are integral to the study of animal ecology. Habitat selection may optimize the fitness of individuals. Hutchinsonian niche theory posits the fundamental niche of species would support the persistence or growth of populations. Although niche‐based species distribution models (SDMs) and habitat suitability models (HSMs) such as maximum entropy (Maxent) have demonstrated fair to excellent predictive power, few studies have linked the prediction of HSMs to demographic rates. We aimed to test the prediction of Hutchinsonian niche theory that habitat suitability (i.e., likelihood of occurrence) would be positively related to survival of American beaver (Castor canadensis), a North American semi‐aquatic, herbivorous, habitat generalist. We also tested the prediction of ideal free distribution that animal fitness, or its surrogate, is independent of habitat suitability at the equilibrium. We estimated beaver monthly survival probability using the Barker model and radio telemetry data collected in northern Alabama, United States from January 2011 to April 2012. A habitat suitability map was generated with Maxent for the entire study site using landscape variables derived from the 2011 National Land Cover Database (30‐m resolution). We found an inverse relationship between habitat suitability index and beaver survival, contradicting the predictions of niche theory and ideal free distribution. Furthermore, four landscape variables selected by American beaver did not predict survival. The beaver population on our study site has been established for 20 or more years and, subsequently, may be approaching or have reached the carrying capacity. Maxent‐predicted increases in habitat use and subsequent intraspecific competition may have reduced beaver survival. Habitat suitability‐fitness relationships may be complex and, in part, contingent upon local animal abundance. Future studies of mechanistic SDMs incorporating local abundance and demographic rates are needed.     

Genetic structure,spatial organization,and dispersal in two populations of bat‐eared foxes

We incorporated radio‐telemetry data with genetic analysis of bat‐eared foxes (Otocyon megalotis) from individuals in 32 different groups to examine relatedness and spatial organization in two populations in South Africa that differed in density, home‐range sizes, and group sizes. Kin clustering occurred only for female dyads in the high‐density population. Relatedness was negatively correlated with distance only for female dyads in the high‐density population, and for male and mixed‐sex dyads in the low‐density population. Home‐range overlap of neighboring female dyads was significantly greater in the high compared to low‐density population, whereas overlap within other dyads was similar between populations. Amount of home‐range overlap between neighbors was positively correlated with genetic relatedness for all dyad‐site combinations, except for female and male dyads in the low‐density population. Foxes from all age and sex classes dispersed, although females (mostly adults) dispersed farther than males. Yearlings dispersed later in the high‐density population, and overall exhibited a male‐biased dispersal pattern. Our results indicated that genetic structure within populations of bat‐eared foxes was sex‐biased, and was interrelated to density and group sizes, as well as sex‐biases in philopatry and dispersal distances. We conclude that a combination of male‐biased dispersal rates, adult dispersals, and sex‐biased dispersal distances likely helped to facilitate inbreeding avoidance in this evolutionarily unique species of Canidae.     

Spatially variable habitat quality contributes to within‐population variation in reproductive success

Variation in habitat quality is common across terrestrial, freshwater, and marine habitats. We investigated how habitat quality influenced the reproductive potential of mud crabs across 30 oyster reefs that were degraded to different extents. We further coupled this field survey with a laboratory experiment designed to mechanistically determine the relationship between resource consumption and reproductive performance. We show a >10‐fold difference in average reproductive potential for crabs across reefs of different quality. Calculated consumption rates for crabs in each reef, based on a type II functional response, suggest that differences in reproductive performance may be attributed to resource limitation in poor quality reefs. This conclusion is supported by results of our laboratory experiment where crabs fed a higher quality diet of abundant animal tissue had greater reproductive performance. Our results demonstrate that spatial variation in habitat quality can be a considerable contributor to within‐population individual variation in reproductive success (i.e., demographic heterogeneity). This finding has important implications for assessing population extinction risk.     

Contrasting reproductive traits in two species of mangrove‐dwelling littorinid snails in a seasonal tropical habitat

Previous studies on the reproductive biology of littorinid snails have focused on rocky shore species, investigating how these gastropods can achieve maximal reproductive success, as well as on processes of sexual selection. This study documented differences in the reproductive traits of two mangrove‐dwelling littorinids, Littoraria ardouiniana and L. melanostoma, in Hong Kong. Reproductive activity of both species was most intense during the summer months. Mating pairs of the two species generally occurred in the tree canopies. Few false mating pairs (same sex or heterospecific pairs: <10%) were recorded, and members of both species showed size‐assortative mating. Littoraria ardouiniana had a shorter reproductive season but a higher intensity of mating and higher seasonal fecundity, than did L. melanostoma. Members of both species showed bi‐lunar periodicities of egg or larval release, synchronized with spring tides. Fecundity showed a strong positive relationship with body size in L. ardouiniana, but not in L. melanostoma. Females of L. ardouiniana released entire broods of larvae in a single brief event, whereas females of L. melanostoma released fewer eggs over 1–8 d. Release of larvae in L. ardouiniana involved a series of short bursts and was much faster than the trickle release of eggs in L. melanostoma. The contrasting reproductive traits in these two species represent different strategies to optimize reproductive success in mangrove habitats.     

Responses by Central‐Place Foragers to Manipulations of Brood Size: Parent Flickers Respond to Proximate Cues but do not Increase Work Rate

Manipulations of brood size measure the willingness or ability of parents to invest in offspring and different reproductive roles may lead to differences in feeding effort between the sexes. Parental investment in birds is usually assessed by quantifying feeding rates, but this provides an incomplete picture of parental effort because it fails to account for how parents collect food on the landscape. We studied northern flickers (Colaptes auratus), a woodpecker in which males provide the majority of parental care and used a repeated measures design and short‐term (24 h) brood enlargements (N = 35) and reductions (N = 27) to assess effects of treatment on feeding rates to nestlings and parental foraging behaviour. Parents of enlarged broods did not significantly increase feeding rate, resulting in a decline in nestling mass. Parents of reduced broods decreased their feeding rates by 84%, but increased per capita feeding rates, resulting in nestling mass gain. The variation in feeding rates to enlarged broods was not influenced by feather corticosterone, body condition, feather re‐growth rate or mass change between the incubation and nestling periods. Foraging pattern on the landscape remained the same during the enlarged treatment for both sexes. We conclude that flickers respond to proximate cues in brood demands, but do not increase feeding rates to enlarged broods, at least in the short term. A literature review suggested that this lack of response is atypical for short‐lived species. We hypothesize that parents in species with large home ranges and long nestling periods face energetic limitations that constrain their ability to respond to enlarged broods. We encourage future studies to assess foraging behaviour on the landscape to document important trade‐offs for parents such as predation risk and energy expenditure while feeding offspring.     

Changes in habitat selection patterns of the gray partridge Perdix perdix in relation to agricultural landscape dynamics over the past two decades

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Comparing constitutive and induced costs of symbiont‐conferred resistance to parasitoids in aphids

Host defenses against parasites do not come for free. The evolution of increased resistance can be constrained by constitutive costs associated with possessing defense mechanisms, and by induced costs of deploying them. These two types of costs are typically considered with respect to resistance as a genetically determined trait, but they may also apply to resistance provided by ‘helpers’ such as bacterial endosymbionts. We investigated the costs of symbiont‐conferred resistance in the black bean aphid, Aphis fabae (Scopoli), which receives strong protection against the parasitoid Lysiphlebus fabarum from the defensive endosymbiont Hamiltonella defensa. Aphids infected with H. defensa were almost ten times more resistant to L. fabarum than genetically identical aphids without this symbiont, but in the absence of parasitoids, they had strongly reduced lifespans, resulting in lower lifetime reproduction. This is evidence for a substantial constitutive cost of harboring H. defensa. We did not observe any induced cost of symbiont‐conferred resistance. On the contrary, symbiont‐protected aphids that resisted a parasitoid attack enjoyed increased longevity and lifetime reproduction compared with unattacked controls, whereas unprotected aphids suffered a reduction of longevity and reproduction after resisting an attack. This surprising result suggests that by focusing exclusively on the protection, we might underestimate the selective advantage of infection with H. defensa in the presence of parasitoids.     

Location of long‐term communal burrows of a threatened arid‐zone lizard in relation to soil and vegetation

The great desert skink (Liopholis kintorei) of the Egerniinae subfamily (Reptilia: Scincidae) is a communal burrowing lizard that inhabits arid spinifex grasslands in central Australia. Great desert skink activity is centred in and around the burrows which are inhabited for many years. However, it is not known whether skinks select burrow sites with specific attributes or how continuing occupancy of burrows is influenced by the surrounding habitat; especially post‐fire, when plant cover is reduced. Here, we test whether great desert skink burrows in areas burnt 2 years previously and in longer unburnt areas are associated with particular habitat attributes, and whether there are differences between occupied and recently abandoned burrow sites. Vegetation composition, cover and soil surface characteristics at 56 established great desert skink burrows, including occupied and recently unoccupied burrows, were compared with 56 random nearby non‐burrow control sites. Burrow sites had higher plant cover compared with the surrounding landscape in both recently burnt and longer unburnt areas and were more likely to be associated with the presence of shrubs. Soil stability and infiltration were also higher at burrow sites. However, we found no evidence that burrows with lower cover were more likely to be abandoned. Our results suggest that great desert skinks may actively select high cover areas for burrow construction, although differences between burrow and control sites may also partly reflect local changes to plant cover and composition and soil properties resulting from burrow construction and long‐term habitation of a site. Further research should determine if burrows with shrubs or higher plant cover provide greater protection from predators, more structural stability for burrow construction, increased prey abundance or other benefits. We recommend that maintenance of areas with relatively higher plant cover be prioritized when managing great desert skink habitat.     

Mass‐rearing conditions do not affect responsiveness to sex pheromone and flight activity in sweetpotato weevils

For ensuring the effectiveness of sterile insect technique (SIT) programmes, maintaining the reproductive competitiveness and dispersal ability of mass‐reared sterile males is essential. Inadvertent selection is an important genetic process that frequently occurs during mass rearing to produce sterile males. We investigated the effect of mass‐rearing conditions on the responsiveness to sex pheromones and spontaneous flight activity of males of the sweetpotato weevil Cylas formicarius (Coleoptera: Brentidae). There were no significant differences in the responsiveness to sex pheromones and spontaneous flight activity between wild and mass‐reared strains. These results indicate that mass‐reared strains of C. formicarius might not cause serious problems for implementing SIT programmes.     

Adverse effects of agricultural intensification and climate change on breeding habitat quality of Black‐tailed Godwits Limosa l. limosa in the Netherlands

Agricultural intensification is one of the main drivers of farmland bird declines, but effects on birds may be confounded with those of climate change. Here we examine the effects of intensification and climate change on a grassland breeding wader, the Black‐tailed Godwit Limosa l. limosa, in the Netherlands. Population decline has been linked to poor chick survival which, in turn, has been linked to available foraging habitat. Foraging habitat of the nidifugous chicks consists of uncut grasslands that provide cover and arthropod prey. Conservation measures such as agri‐environment schemes aim to increase the availability of chick foraging habitat but have not yet been successful in halting the decline. Field observations show that since the early 1980s, farmers advanced their first seasonal mowing or grazing date by 15 days, whereas Godwits did not advance their hatching date. Ringing data indicate that between 1945 and 1975 hatching dates advanced by about 2 weeks in parallel with the advancement of median mowing dates. Surprisingly, temperature sums at median mowing and hatching dates suggest that while the agricultural advancement before 1980 was largely due to agricultural intensification, after 1980 it was largely due to climate change. Examining arthropod abundance in a range of differently managed grasslands revealed that chick food abundance was little affected but that food accessibility in intensively used tall swards may be problematic for chicks. Our results suggest that, compared with 25 years ago, nowadays (1) a much higher proportion of clutches and chicks are exposed to agricultural activities, (2) there is little foraging habitat left when chicks hatch and (3) because of climate change, the vegetation in the remaining foraging habitat is taller and denser and therefore of lower quality. This indicates that for agri‐environment schemes to make a difference, they should not only be implemented in a larger percentage of the breeding area than the current maxima of 20–30% but they should also include measures that create more open, accessible swards.     

Reproductive trade‐offs in a long‐lived bird species: condition‐dependent reproductive allocation maintains female survival and offspring quality

Life history theory is an essential framework to understand the evolution of reproductive allocation. It predicts that individuals of long‐lived species favour their own survival over current reproduction, leading individuals to refrain from reproducing under harsh conditions. Here we test this prediction in a long‐lived bird species, the Siberian jay Perisoreus infaustus. Long‐term data revealed that females rarely refrain from breeding, but lay smaller clutches in unfavourable years. Neither offspring body size, female survival nor offspring survival until the next year was influenced by annual condition, habitat quality, clutch size, female age or female phenotype. Given that many nests failed due to nest predation, the variance in the number of fledglings was higher than the variance in the number of eggs and female survival. An experimental challenge with a novel pathogen before egg laying largely replicated these patterns in two consecutive years with contrasting conditions. Challenged females refrained from breeding only in the unfavourable year, but no downstream effects were found in either year. Taken together, these findings demonstrate that condition‐dependent reproductive allocation may serve to maintain female survival and offspring quality, supporting patterns found in long‐lived mammals. We discuss avenues to develop life history theory concerning strategies to offset reproductive costs.     

Occurrence,costs and heritability of delayed selfing in a free‐living flatworm

Evolutionary theory predicts that in the absence of outcrossing opportunities, simultaneously hermaphroditic organisms should eventually switch to self‐fertilization as a form of reproductive assurance. Here, we report the existence of facultative self‐fertilization in the free‐living flatworm Macrostomum hystrix, a species in which outcrossing occurs via hypodermic insemination of sperm into the parenchyma of the mating partner. First, we show that isolated individuals significantly delay the onset of reproduction compared with individuals with outcrossing opportunities (‘delayed selfing’) as predicted by theory. Second, consistent with the idea of M. hystrix being a preferential outcrosser under natural conditions, we report likely costs of selfing manifested via reduced hatchling production and offspring survival. Third, we demonstrate that selfing propensity has a genetic basis in this species, with a heritability estimated at 0.43 ± 0.11. Variation in selfing propensity could arise due to differing costs of inbreeding among families; despite marked inter‐family variation in apparent costs of inbreeding, we found no evidence for such a link. Alternatively, selfing propensity might differ across families because of heritable variation in reproductive traits that determine the likelihood of selfing. We speculate that adaptations to hypodermic insemination under outcrossing, most notably a highly modified copulatory stylet (male copulatory organ) and reduced sperm complexity, could also facilitate facultative selfing in this species.     

Human activity and habitat type affect perceived predation risk in urban white‐footed mice (Peromyscus leucopus)

Predation risk is one of the largest costs associated with foraging in small mammals. Small mammals select microhabitat features such as tree and shrub canopy cover, woody debris and vegetative ground cover that can lower the risk of detection from predators and provide greater protection if discovered. Small mammals also increase foraging activity and decrease selection for cover when cloud cover increases and moon illumination is less. Often researchers assume small mammals in urban areas respond to these cues in the same manner as in natural areas, but these cues themselves are altered in urban zones. In this study, we investigated how Amur honeysuckle (Lonicera maackii) and coarse woody debris (CWD) affected giving‐up density (GUD) in white‐footed mice (Peromyscus leucopus). Each of three habitat treatments (open flood channel, the edge and interior of the honeysuckle patch) contained cover treatments with coarse woody debris present or absent. The six treatment combinations were compared to environmental variables (temperature, humidity and illumination) and habitat variables to test their effect on GUD. Peromyscus leucopus foraged to lower densities in areas with CWD present and also under the honeysuckle canopy, using this invasive shrub to decrease predation risk, potentially increasing survivability within this urban park. Increased human presence negatively affected foraging behavior across treatments. Human presence and light pollution significantly influenced P. leucopus, modifying their foraging behavior and demonstrating that both fine‐ and coarse‐scale urban factors can affect small mammals. Foraging increased as humidity increased, particularly under the honeysuckle canopy. Changes in illumination due to moonlight and cloud cover did not affect foraging behavior, suggesting urban light pollution may have altered behavioral responses to changes in light levels. Lonicera maackii seemed to facilitate foraging in P. leucopus, even though it adversely affects the plant community, suggesting that its impact may not be entirely negative.