Pablo M. Vergara

Kestrel-Prey Dynamic in a Mediterranean Region: The Effect of Generalist Predation and Climatic Factors

Background Most hypotheses on population limitation of small mammals and their predators come from studies carried out in northern latitudes, mainly in boreal ecosystems. In such regions, many predators specialize on voles and predator-prey systems are simpler compared to southern ecosystems where predator communities are made up mostly of generalists and predator-prey systems are more complex. Determining food limitation in generalist predators is difficult due to their capacity to switch to alternative prey when the basic prey becomes scarce. Methodology We monitored the population density of a generalist raptor, the Eurasian kestrel Falco tinnunculus over 15 years in a mountainous Mediterranean area. In addition, we have recorded over 11 years the inter-annual variation in the abundance of two main prey species of kestrels, the common vole Microtus arvalis and the eyed lizard Lacerta lepida and a third species scarcely represented in kestrel diet, the great white-toothed shrew Crocidura russula. We estimated the per capita growth rate (PCGR) to analyse population dynamics of kestrel and predator species. Principal Findings Multimodel inference determined that the PCGR of kestrels was better explained by a model containing the population density of only one prey species (the common vole) than a model using a combination of the densities of the three prey species. The PCGR of voles was explained by kestrel abundance in combination with annual rainfall and mean annual temperature. In the case of shrews, growth rate was also affected by kestrel abundance and temperature. Finally, we did not find any correlation between kestrel and lizard abundances. Significance Our study showed for the first time vertebrate predator-prey relationships at southern latitudes and determined that only one prey species has the capacity to modulate population dynamics of generalist predators and reveals the importance of climatic factors in the dynamics of micromammal species and lizards in the Mediterranean region.

Heavy metals in northern Chilean rivers: spatial variation and temporal trends.

Rivers of central-northern Chile are exposed to pollution from different sources, including mining activities, natural orogenic process, volcanic activity, and geology. In order to determine the contribution of mining to river pollution, the spatio-temporal dynamics of chemical species dissolved in 12 rivers of central-northern Chile was assessed. Of all the rivers studied, the Elqui showed the highest historical mean concentrations of As, Cu and Pb. The Aconcagua had the highest concentration of Hg and a large Cr concentration, while the Rapel showed elevated concentrations of Cu and Mo. The Elqui and the Aconcagua were clustered as distinct groups by a cluster analysis based on two independent principal components. Hierarchical Bayesian models showed annual trends but no seasonal effects in heavy metal concentrations. As and Cu in the Elqui had positive annual slopes. Sulphate concentration exceeded 100 mg L(-1) in nine rivers, and in seven of them it had positive annual slopes. Our findings suggest that mining pollution is the main process contributing to this increasing annual trend in As, Cu and SO(4)(2-). Therefore, in order to improve the water quality of these rivers it is necessary to identify the main sources of heavy metals associated with mining activities.

Delayed plumage maturation in Eurasian kestrels : female mimicry, subordination signalling or both?

Delayed plumage maturation (DPM) of young males in sexually dichromatic birds has been explained under the female mimicry hypothesis (FMH) or the subordination signalling hypothesis (SbSH), among other adaptive ideas proposed. In this study, we tested in the Eurasian kestrel, Falco tinnunculus, the predicted sexual deception and aggressiveness under the FMH and SbSH to explain DPM in birds. We analysed aggressive and courtship behaviour of breeding males and females in the presence of adult male, adult female and 1-year-old male natural decoys. We designed two different treatments: one presenting un-moulted 1-year-old males and a second presenting partly moulted 1-year-old males, as observed in nature. Males attacked adult male decoys more frequently than 1-year-old male and female decoys in both moulted and un-moulted treatments and no sexual displays were observed. Females were more aggressive towards female and 1-year-old male decoys as compared to male decoys in the un-moulted treatment. In the moulted treatment, females were more aggressive towards female decoys as compared to both male decoys. In addition, females solicited copulas from moulted, but not from un-moulted, 1-year-old male decoys. Our results suggest that FMH can be a mechanism which explains DPM in un-moulted 1-year-old males. However, when they show moulted plumage (more than 80% in the studied population during the spring), the SbSH seems to be the mechanism that better explains sexual and agonistic behaviour from adults towards 1-year-old males.

Habitat selection and population trends in terrestrial bird species of Robinson Crusoe Island: habitat generalists versus forest specialists

Habitat loss and degradation on oceanic islands are key processes leading to population decline of endemic birds and facilitating the establishment of invasive bird species. In this study, carried out in the Robinson Crusoe Island, we assessed density and habitat selection of terrestrial bird species, including juan fernandez firecrown and juan fernandez tit-tyrant, two endemics, as well as green-backed firecrown and austral thrush, which apparently originate from the mainland. Results show that perturbed habitats contained a low density of the endemic species whereas the mainland species were significantly more abundant in perturbed scrub habitats. Bird species show different habitat selection patterns, with endemics selecting for native forest and mainland species selecting for perturbed habitats, or using them at random. Bird species experienced temporal trends in their overall population sizes, with the endemic tit-tyrant suffering a significant decline in its population size of about 63% between 1994 and 2009. Only mainland species exhibited temporal changes in habitat use, significantly reducing their densities in the preferred scrub habitats, possibly as a response to decreased habitat quality. Thrushes apparently were able to compensate the population decrease in one non native habitat type by using native forests, a habitat giving them the opportunity of preying on nests of endemic species. We conclude that endemic bird species behave as specialists whereas the mainland species must be treated as invasive generalists on Robinson Crusoe Island.

Effects of maternal carotenoid availability in relation to sex, parasite infection and health status of nestling kestrels (Falco tinnunculus)

SUMMARY Mothers can strongly influence the development of their offspring, and if maternal resources are limited, they may influence optimal reproductive strategies. In birds, maternally deposited carotenoids are a prominent component of egg yolk and are vital for the development of the embryo. However, results of long-lasting fitness consequences of this early nutritional environment have been scarce and inconsistent. In addition, sex-biased sensitivity to different egg components is one of the mechanisms postulated to account for sex-linked environmental vulnerability during early life. However, this important aspect is usually not accounted for when investigating maternal investment in carotenoids. In this study we gave carotenoid (lutein) supplements to female Eurasian kestrels (Falco tinnunculus) before and during egg laying. The experiment increased female plasma carotenoids, but this effect was not apparent in hatchling and fledgling plasma carotenoid concentration. Also, results showed that carotenoid supplementation increased the high density lipoprotein to low density lipoprotein ratio in adult females, suggesting that dietary carotenoids may influence lipid metabolism. Furthermore, the effect of the treatment was manifested in several nestling health state parameters. Nestlings of carotenoid-supplemented females were infested by less intestinal parasite groups, had higher lymphocyte concentrations in blood plasma, and were less stressed (heterophile to lymphocyte ratio) than control nestlings. In addition, an interaction between the experimental treatment and nestling sex was apparent for globulin concentrations, favouring the smaller male nestlings. Thereby, suggesting that males benefited more than females from an increase in maternal carotenoid investment. Our study shows that an increase in carotenoids in the maternal diet during egg laying favours nestling development in kestrels, and may also affect nestlings in a sex-specific way.

Nest Size, Nest Building Behaviour and Breeding Success in a Species with Nest Reuse: The White Stork Ciconia ciconia

Nest size and nest building behaviour affect individual fitness and thus, selection may act on these traits. Most data on nesting behaviour come from species that build a nest for each new breeding attempt, whereas almost nothing is known regarding nest reusers. Here, the association between nest size and nest building behaviour, and occupation date as well as breeding success of the white stork Ciconia ciconia, a migratory species with nest reuse, is presented. Large nests were occupied earlier and showed higher breeding success, even accounting for the confounding effect of the breeders age. In addition, nest size increased steadily over the entire breeding season and only ceased when reproduction failed. However, this increase was not related to breeding success variables. Finally, nest size was related to the number of times that it was used in the past and thus, to the probability of successful reproduction. These results suggest that storks may seek and compete for bigger nests and that nest size could be an indicator of individual and/or nest-site quality.

Parasitized Mates Increase Infection Risk for Partners

Individuals can gain fitness benefits and costs through their mates. However, studies on sexual selection have tended to focus on genetic benefits. A potentially widespread cost of pairing with a parasitized mate is that doing so will increase an individual’s parasite abundance. Such a cost has been overlooked in systems in which parasites are indirectly transmitted. We manipulated the abundance of the nematode parasite Trichostrongylus tenuis, an indirectly transmitted parasite, within pairs of wild red grouse Lagopus lagopus scoticus in spring. Parasite levels were correlated within pairs before the experiment. We removed parasites from males, females, or both members of the pair and evaluated individual parasite uptake over the subsequent breeding period. At the end of the breeding season, an individual’s parasite abundance was greater when its mate had not been initially purged of parasites. This cost appeared to be greater for males. We discuss the implications of our results in relation to the costs that parasites may have on sexual selection processes.

Frugivory on Persea lingue in temperate Chilean forests: interactions between fruit availability and habitat fragmentation across multiple spatial scales.

Habitat degradation and fragmentation are expected to reduce seed dispersal rates by reducing fruit availability as well as the movement and abundance of frugivores. These deleterious impacts may also interact with each other at different spatial scales, leading to nonlinear effects of fruit abundance on seed dispersal. In this study we assessed whether the degradation and fragmentation of southern Chilean forests had the potential to restrict seed dispersal the lingue (Persea lingue) tree, a fleshy-fruited tree species. Of five frugivore bird species, the austral thrush (Turdus falcklandii) and the fire-eyed diucon (Xolmis pyrope) were the only legitimate seed dispersers as well as being the most abundant species visiting lingue trees. The results showed little or no direct effect of habitat fragmentation on seed dispersal estimates, possibly because the assemblage of frugivore birds was comprised habitat-generalist species. Instead, the number of fruits removed per focal tree exhibited an enhanced response to crop size, but only in the more connected fragments. In the fruit-richer fragment networks, there was an increased fragment-size effect on the proportion of fruits removed in comparison to fruit-poor networks in which the fragment size effect was spurious. We suggest that such nonlinear effects are widespread in fragmented forest regions, resulting from the link between the spatial scales over which frugivores sample resources and the spatial heterogeneity in fruiting resources caused by habitat fragmentation and degradation.

Agonistic behaviour prior to laying predicts clutch size in Eurasian kestrels: an experiment with natural decoys

Aggressive behaviour against conspecifics is considered a costly behaviour that forms part of reproductive investment. Previous studies have suggested that the intensity of agonistic behaviour may indicate individual quality since it exhibits a positive correlation with brood value. However, this relationship has been demonstrated after clutch completion, and by creating a nexus between efforts it has not been possible to disentangle other hypotheses that could explain such findings. Here, by presenting a trio of natural decoys (adult male, adult female and 1-year-old male) to Eurasian kestrels, Falco tinnunculus, we tested whether the aggressive behaviour to conspecifics prior to laying predicted posterior reproductive performance (clutch size). We also tested the effect of breeding stage and breeding density on this behaviour. In addition, we examined the effect of the presence of moulted versus unmoulted 1-year-old males on aggressive behaviour of breeders. Intrasexual agonistic behaviour, measured as attack intensity to the decoys, was positively correlated with clutch size in females, but negatively in males. In males, aggressive behaviour was lower during the female fertile stage than during previous stage, but in females, was similar over stages. Furthermore, agonistic behaviour increased with breeding density in females but not in males. We discuss these results in the context of sexual selection theory, and propose that the link between agonistic behaviour prior to laying and clutch size is via the connection to courtship feeding and that may be considered as an indicator of individual quality for both sexes.

Matrix-dependent corridor effectiveness and the abundance of forest birds in fragmented landscapes

Corridor function for wildlife movement constitutes an important and desirable ecological characteristic of linear landscape structures. Changes in the matrix conditions, however, may result in substantial changes in the mechanisms responsible for the use of corridors by animals. I developed a model that describes the influence of matrix quality on the effectiveness of corridors for wildlife movement and the abundance of animals in the corridors. The model predicts that corridor effectiveness is maximized at intermediate matrix quality levels, while the abundance in the corridor increases asymptotically with matrix quality. I tested predictions of this model by comparing the expected and observed relative abundance of forest bird species in two landscape types of southern Chile. In nine out of 12 cases the model correctly predicted the relative abundance of forest birds. Riparian forest strips were expected to be effective functioning as corridors for five out of six studied species, although corridor effectiveness for each species varied between landscape types. A reasonable strategy to improve connectivity is to maintain (or to increase, if necessary) the matrix quality at a level such that corridors can function efficiently as both drift fences and movement conduits.