Fabrizio Sergio

Conservation: top predators and biodiversity.

The charisma of top vertebrate predators is often used by conservationists as a lever for financial support, to raise environmental awareness and in planning protected areas — a strategy that has been criticized. Here we use information collected from five raptor species that differ widely in their diet and habitat associations to show that sites occupied by these predators are consistently associated with high biodiversity. The biodiversity at these sites is more extensive than it is at sites selected at random, or at sites occupied by species from lower down the trophic pyramid (insectivorous or herbivorous species, for example). Our results indicate that conservation focusing on top predators can be ecologically justified because it delivers broader biodiversity benefits.

Environmental stochasticity in dispersal areas can explain the ‘mysterious’ disappearance of breeding populations

We present the results of an individual-based simulation model, showing that increasing the mortality of non-breeding dispersers within settlement areas can lead to the extinction of species and (meta)populations in a subtle way. This is because the areas where dispersers settle are generally unknown or difficult to detect. Consequently, fewer efforts are devoted to the conservation of these sites than to the conservation of breeding territories. Additionally, high mortality rates affecting the floater sector of a population become evident in the breeding sector only after several of years, when it is too difficult or too late to halt the decline. As a result, because most conservation projects on endangered species and populations mainly focus on breeding areas, many current efforts may be wasted in locations other than those in which conservation would be really necessary and effective.

Regional conservation priorities for a large predator: golden eagles (Aquila chrysaetos) in the Alpine range

We compared the density of golden eagles (Aquila chrysaetos) and their nest dispersion, productivity and diet in Alpine and pre-Alpine areas. The comparison was made at two spatial scales: (1) at the territory level within two contiguous populations, and (2) at the population level, using published data for 22 populations scattered across four countries (France, Switzerland, Germany and Italy). Availability of golden eagles main prey species was higher in Alpine than in pre-Alpine regions. The potential foraging ranges of pairs of eagles in the pre-Alps had larger amounts of woodland and lower amounts of suitable foraging habitat than those of Alpine pairs. At both spatial scales, density and productivity were lower in the pre-Alps. Also, pre-Alpine populations were characterised by a lower percentage of main prey species in the diet, which was significantly correlated with productivity, and by a higher breadth of diet, which was negatively correlated with density. Overall, higher prey availability and habitat suitability in the Alps resulted in higher density and breeding success, in a manner compatible with theoretical metapopulation models. We suggest that priority be given to conservation of eagle populations in high quality Alpine habitat, and that conservation action be carried out by a mixture of site-protection measures and conservation of the wider environment.

From individual behaviour to population pattern: weather-dependent foraging and breeding performance in black kites

Abstract The links between weather and animal behaviour in population processes have received relatively little attention. I studied the effect of weather conditions on foraging and breeding performance of a medium-sized raptor, the black kite, Milvus migrans . The frequency of prey capture attempts and their likelihood of success increased with temperature and declined with rainfall. Kites used flight styles involving a higher energy expenditure in less favourable weather. Nestling provisioning rates declined during rain spells. More kites hunted during periods of favourable weather and after periods with a high frequency of successful prey capture attempts by conspecifics; this result suggested that individuals may fine-tune their foraging effort to the expected foraging reward. Such compensatory behavioural adjustments may increase species resilience to climate change. The behaviourally mediated effects of weather on prey availability translated into population effects. Yearly weather conditions during the last stage of the prelaying period affected population-level productivity, probably through an effect on female body condition mediated by male provisioning capability and hunting yield. The predicted effects of climate change on kites may already be occurring, with progressively earlier laying and northward range expansion. These results confirm the need to pay greater attention to behaviourally mediated effects of climate on populations, particularly when individuals make compensatory adjustments that may enhance resilience to climate change. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Reconciling the dichotomy between single species and ecosystem conservation: black kites (Milvus migrans) and eutrophication in pre-Alpine lakes

In recent times there has been a growing dichotomy between preservation of single species and broader, ecosystem-based approaches to conservation. Freshwater habitats are among the most highly human-impacted ecosystems. We used a long-term data set on black kites (Milvus migrans), a threatened raptor dependent on aquatic habitats, to explore ways to reconcile single species and biodiversity-driven approaches to conservation. In the pre-Alpine lakes of northern Italy, black kite populations showed medium-low density, extremely low breeding success and widespread declines. Spatio-temporal variations showed density and breeding success to be positively related to ecosystem productivity (as estimated by phosphorus concentrations in lakes), availability of aquatic habitats and grassland, and to be negatively related to extent of farmland and fish harvest by professional fishermen. Fish species richness, used as a surrogate of biodiversity, was highest in one oligotrophic lake, but on average increased with increasing ecosystem productivity (i.e. lake eutrophication). Given expected future declines in ecosystem productivity, kite conservation will be helped by enhancing populations of alternative prey in terrestrial habitats (e.g. through incentives for grassland), and higher regulation of fish harvest. On the other hand, ecosystem management may profit from the use of black kites or other aerial piscivores as indicators of biodiversity and of diffuse ecosystem stress, such as sustainability of fishing practices.

Biases in population diet studies due to sampling in heterogeneous environments: a case study with the Eagle Owl

Abstract Many studies have reported variation in bird diet composition related to spatial variation in habitat quality and landscape heterogeneity. Most diet analyses involve collection of food items at a sub-sample of available sites. Because individuals at different sites may vary in their diet composition, the description of the diet of a population may depend on which sites are sampled. This potential bias associated with environmental heterogeneity has never been explicitly tested. We used dietary data from a long-term study of an owl population to simulate various scenarios of diet assessment in which the investigator samples food items from various sites without taking into account their variation in quality. The simulations showed that assessment of diet composition was highly dependent on the number and type of sites sampled for food items and that such bias caused by environmental heterogeneity disappeared when food samples were randomly collected at more than 60% of the available sites. Biases in diet description may affect a large number of studies, especially of territorial species in heterogeneous landscapes. Similar biases may apply to the assessment of demographic parameters.

Density, productivity, diet and population status of the Peregrine Falcon Falco peregrinus in the Italian Alps

Capsule The population of Peregrine Falcon in the central-eastern Italian Alps is much larger than previously thought. Aims To assess the status of the species in the Alps and re-estimate the overall Italian population size. Methods We monitored a Peregrine Falcon population of 45 territorial pairs between 1998 and 2003 in a 3570 km2 study area located in the central-eastern Italian Alps. Results All nests were on large cliffs at a mean elevation of 830 m (range = 250–1950 m). The population trend was stable at a mean density of 1.16 pairs/100 km2. Mean nearest-neighbour distance between territorial pairs was 5.1 km. The percentage of pairs consisting of an adult male and an immature female was low (1.3% of 225 breeding attempts). Mean laying date was 11 March, the percentage of successful pairs was 46%, and the mean number of fledged young was 1.10 per territorial pair and 2.40 per successful pair. Diet was dominated by Turdidae, Columbidae and Corvidae. Density, diet and breeding performance were comparable to those reported for other European populations in the 1980s and 1990s. Conclusion The population of the central-eastern Alps, previously underestimated at 20–30 pairs, is re-estimated at 400–460 pairs. The overall Italian population is consequently re-estimated at 1085–1335 pairs (i.e. about 20% of the European population). The conservation status of the population appears satisfactory.

Implications of temporal changes in forest dynamics on density, nest-site selection, diet and productivity of Tawny Owls Strix aluco in the Alps

Capsule In the areas studied, Tawny Owls showed extreme flexibility and opportunism, occupying most available vegetation types and elevations below the tree-line. Aims To assess habitat relationships for the species so as to forecast the potential impact of habitat changes. Methods We censused a total of 321 territories in 12 study areas covering the regional variation in elevation and the associated heterogeneity in vegetation types and landscape configurations. Results The species occupied virtually all vegetation types and landscape configurations below the tree-line. Nests were mostly located on cliffs, but also in tree cavities, buildings, and stick nests of other raptors. Density varied from 12 to 60 territories/100 km2 and mean nearest-neighbour distance from 0.7 to 1.8 km, depending on the availability of broadleaved woodland. Compared to availability, nests were nearer to cliffs and had higher richness of habitat edges and vegetation types, which positively affected chick production. Diet composition varied widely according to habitat and was mostly dominated by Edible Dormouse Glis glis, voles and mice. Conclusion The conservation status of the species was satisfactory. Future habitat changes may favour an increase in density. Silvicultural practices encouraging more old trees with large cavities would further favour this opportunistic species.

Experimental Tests of Endocrine Function in Breeding and Nonbreeding Raptors

Many long-lived avian species defer reproduction for several years, often displaying a “floating” behavior characterized by the lack of mates and exclusive territories. Understanding the proximate mechanisms regulating floating behavior is a relevant topic of research for physiologists, behavioral ecologists, and population biologists because a prolonged period of nonbreeding can negatively affect lifetime fitness and change population dynamics. Here we tested two hypotheses linking endocrine function to floating status: (a) floaters undergo a period of sexual immaturity characterized by lower gonadal function (hypothesis of sexual immaturity), and (b) floating status is socially imposed by dominant conspecifics and revealed by the adrenocortical response to stress (hypothesis of social subordination). The two hypotheses were tested in a population of free-living black kites Milvus migrans in Doñana National Park (southwest Spain), where breeders coexist with young floaters that defer reproduction for 3–7 yr. Hypophysial-gonadal function, estimated as androgen production in response to experimental challenge with gonadotropin-releasing hormone (c-GnRH-I), was similar in magnitude and timing between floating and breeding males. The same treatment was, however, unable to elicit any response in terms of increasing estradiol or total androgen levels in females regardless of their breeding status. Following experimental capture and restraint, the adrenocortical response to stress (estimated as circulating corticosterone levels) was higher in floating than in breeding males, while females showed the opposite pattern (i.e., lower response to stress in young floaters compared with breeders). Contrary to the hypothesis of sexual immaturity, our results suggest that floating males are physiologically capable of reproducing. The reported differences in adrenocortical function support the idea that floaters are socially subordinate to breeders, and corticosterone responses reflect the sex-specific roles during competition in socially monogamous species.

Different location sampling frequencies by satellite tags yield different estimates of migration performance: pooling data requires a common protocol.

Background Migration research is in rapid expansion and increasingly based on sophisticated satellite-tracking devices subject to constant technological refinement, but is still ripe with descriptive studies and in need of meta-analyses looking for emergent generalisations. In particular, coexistence of studies and devices with different frequency of location sampling and spatial accuracy generates doubts of data compatibility, potentially preventing meta-analyses. We used satellite-tracking data on a migratory raptor to: (1) test whether data based on different location sampling frequencies and on different position subsampling approaches are compatible, and (2) seek potential solutions that enhance compatibility and enable eventual meta-analyses. Methodology/Principal Findings We used linear mixed models to analyse the differences in the speed and route length of the migration tracks of 36 Black kites (Milvus migrans) satellite-tagged with two different types of devices (Argos vs GPS tags), entailing different regimes of position sampling frequency. We show that different location sampling frequencies and data subsampling approaches generate large (up to 33%) differences in the estimates of route length and migration speed of this migratory bird. Conclusions/Significance Our results show that the abundance of locations available for analysis affects the tortuosity and realism of the estimated migration path. To avoid flaws in future meta-analyses or unnecessary loss of data, we urge researchers to reach an agreement on a common protocol of data presentation, and to recognize that all transmitter-based studies are likely to underestimate the actual distance traveled by the marked animal. As ecological research becomes increasingly technological, new technologies should be matched with improvements in analytical capacity that guarantee data compatibility.