Causes of natal dispersal were studied in an isolated population of the migratory, facultatively colonial Lesser Kestrel (Falco naumanni) in northeastern Spain. During a seven‐year study, we gathered information on natal dispersal of 751 individuals and on 24 explanatory variables that evaluated individual traits, conspecific cues in terms of colony size, and different ecological and populational features. We examined separately whether or not individuals changed colonies and how far they moved. Dispersal from the natal colony was high (83%), and dispersers covered a median distance of 7225 m (range 112–136 500 m). The probability of natal dispersal decreased with the size of the natal colony and with the distance to the nearest colony, but not with the distance to unoccupied buildings, in the year of recruitment. Moreover, the shorter the distance to the nearest colony, the shorter the distances that individuals dispersed, particularly to large colonies (>10 pairs). These results support the conspecific attraction hypothesis. Accordingly, the probability of recruiting in the natal colony increased with the proportion of philopatric adults, although beyond a threshold individuals were prevented from recruiting by the more dominant adults in a despotic way. The timing of arrival from the wintering grounds was positively related to the probability of colony change, especially in males. To the extent that this variable is related to the phenotypic quality of individuals, it reinforces the idea that natal dispersal is shaped by intraspecific competition in crowded colonies. Males showed lower frequencies of colony change and dispersed shorter distances than did females, as explained by the different role of the sexes in nest acquisition and defense. Our results indicate that natal dispersal is an evolutionarily labile trait simultaneously influenced by ecological, social, and individual features both within and between populations.

BackgroundThere are few studies of careful examination of wildlife casualties in Wildlife Rehabilitation Centers. These studies are essential for detecting menaces to wild species and providing objective criteria about cost-benefit of treatments in those centers. The release rate is considered the main outcome indicator, but other parameters such as length of stay at the center and a cost-benefit index expressed as number of released animals per euro and day, could be used as reliable estimators of the rehabilitation costs.MethodologyA retrospective study based on 54772 admissions recorded from 1995–2013 in the database of the Wildlife Rehabilitation Center of Torreferrussa (Catalonia, NW Spain) assessed the morbidity, outcomes and cost-benefits of the rehabilitation practices.ResultsThree hundred and two species were included: 232 birds (n = 48633), 37 mammals (n = 3293), 20 reptiles (n = 2705) and 13 amphibians (n = 141). The most frequent causes of admission were: 39.8% confiscation of protected species (89.4% passerines), 31.8% orphaned young animals (35.3% swifts, 21.7% diurnal raptors and owls) and 17.4% trauma casualties (46.7% raptors and owls). The highest proportion of releases was found in the captivity confiscation category [87.4% passerines (median time of stay: 12 days)], followed by the orphaned category [78% owls (66 days), 76.5% diurnal birds of prey (43 days), 75.6% hedgehogs (49 days), 52.7% swifts (19 days) and 52% bats (55 days)]. For the trauma group, 46.8% of releases were hedgehogs (44 days) and 25.6% owls (103 days). As regards the cost-benefit index, the trauma casualties and infectious diseases had the worse values with 1.3 and 1.4 released animals/euro/day respectively, and were particularly low in raptors, waders, marine birds and chiroptera. On the contrary, captivity (4.6) and misplacement (4.1) had the best index, particulary in amphibian, reptiles and passerines.Conclusions/significanceCost-benefit studies including the release rate, the time of stay at the center and the cost-benefit index should be implemented for improving management efficiency of the Wildlife Rehabilitation Centers.

Major conservation efforts in human-dominated systems, such as farmland, have focused on the establishment of subsidies and compensation promoting low-impact management practices to reverse the impacts of conservation threats in the short term (reactive approaches). In this study, we discuss how a different way of framing conservation policy (proactive approaches) could lead to fundamentally different long-term conservation outcomes. We define proactive approaches as those not necessarily including measures directly addressing the threats affecting biodiversity, but promoting transitions from current scenarios in which species are threatened to new states in which the threat is no longer present. We illustrate reactive and proactive approaches using as a case study two contrasting conservation frameworks for a vulnerable farmland bird, the Montagu's harrier (Circus pygargus) in northeastern Spain. This example shows that reactive approaches can lead to "conservation traps," which we defined as situations where the application of biologically focused actions in response to conservation problems results in an unsustainable need to perpetuate the implementation of those actions. Our aim is to offer a fresh perspective on biodiversity conservation in human-dominated systems and to stimulate alternative, more holistic approaches in conservation promoting transitions to new states not requiring long-term active and costly conservation action.

We used microsatellites to assess ongoing captive breeding and reintroduction programs of the lesser kestrel. The extent of genetic variation within the captive populations analysed did not differ significantly from that reported in wild populations. Thus, the application of widely recommended management practices, such as the registration of crosses between individuals in proper stud books and the introduction of new individuals into the genetic pools, has proven satisfactory to maintain high levels of genetic variation. The high rates of hatching failure occasionally documented in captivity can therefore not be attributed to depressed genetic variation. Even though genetic diversity in reintroduced populations did not differ significantly when compared to wild populations either, average observed heterozygosities and inbreeding coefficients were significantly lower and higher, respectively, when compared to the captive demes where released birds came. Monitoring of reproductive parameters during single-pairing breeding and paternity inference within colonial facilities revealed large variations in breeding success between reproductive adults. The relative number of breeding pairs that contributed to a large part of captiveborn birds (50-56%) was similar in both cases (28.6 and 26.9%, respectively). Thus, the chances for polygyny (rarely in this study), extra-pair paternity (not found in this study) and/or social stimulation of breeding parameters do not seem to greatly affect the genetically effective population size. Independently of breeding strategies, the release of unrelated fledglings into the same area and the promotion of immigration should be mandatory to counteract founder effects and avoid inbreeding in reintroduced populations of lesser kestrels.

Many threatened species in human-dominated systems are managed through conservation programs. Such programs are sometimes designed based on intuition or short-term results rather than assessing their long-term biological and economic sustainability. The current conservation program for Montagu's harriers Circus pygargus, a ground-nesting bird of prey, in Lleida (Catalonia, NE Spain) aims to protect nests located in farmlands by promoting crop harvest delay around the nest and compensating farmers for their economic loss. This program has been flagged as a 'conservation trap' as its costs have been increasing over time, possibly compromising the long-term sustainability of the program and associated consequences to the local harrier population. In the present work, population viability analyses (PVA) were used to find a conservation management scenario that decreases the risk of the conservation trap, or at least minimizes the medium-term expenditure on conservation. PVA simulations suggest that the current nest protection program is financially unsustainable at the medium-term. Cost-effectiveness analyses suggest that it would be impossible to fully avoid the conservation trap if the conservation goal is to maintain Lleida's current population size. Alternative management scenarios that minimize the medium-term expenditure of scarce conservation funds are presented. The results suggest that selecting a conservation program based only on short-term biological or cost-effective targets might not be the most appropriate, and demonstrate the relevance of having clear medium-term conservation targets.