No abstract

In the global scenario of increasing habitat fragmentation, finding appropriate indicators of population viability is a priority for conservation. We explored the potential of learned behaviours, specifically acoustic signals, to predict the persistence over time of fragmented bird populations. We found an association between male song diversity and the annual rate of population change, population productivity and population size, resulting in birds singing poor repertoires in populations more prone to extinction. This is the first demonstration that population viability can be predicted by a cultural trait (acquired via social learning). Our results emphasise that cultural attributes can reflect not only individual-level characteristics, but also the emergent population-level properties. This opens the way to the study of animal cultural diversity in the increasingly common human-altered landscapes.

Individuals of some species differentiate each other on the basis of the acoustic features of their vocalizations, and this can be used in individual-based population monitoring studies. No research has tested for the effectiveness of individual marking through voice recognition as compared to traditional monitoring methods relying on physical marks. We compared voice recognition and physical marking using the Dupont's lark Chersophilus duponti as a study species. This bird needs to be attracted with playback in order to be seen (or captured). We first demonstrated that the territorial calls from a sample of banded males were individually distinctive and constant over time by means of discriminant function analysis, which correctly classified 100% of marked males. Then, we applied similarity techniques on call spectrotemporal features to define a threshold value of similarity within banded individuals, to be combined with qualitative spectrogram inspection for the classification of all recorded birds. Eventually, we compared the voice and the capture samples, to test for differences in relation to re-location rate, territory fidelity and dispersal movements both within and between years. Voice recognition was less time-consuming than capture-recapture method in the field, but it was useless for monitoring yearlings in call development stage. The two methods provided the same results in terms of territory fidelity and dispersal movements, but differed in re-location rates, which were significantly greater in the case of voice recognition method. By means of physical captures we possibly trapped a large sample of young and silent floaters, with low probability of recapture or recording. This mismatch between methods could bias the estimates of annual survival, which strongly depend on re-location rates. We suggest considering the two methods as complementary rather than alternatives for monitoring populations. Each technique offers unique information, and the two sources should be combined to provide correction factors that would eventually sharpen our knowledge on bird population ecology.

The European population of Dupont's lark Chersophilus duponti, restricted to Spanish steppe, was estimated to be 13,000 pairs in c. 50 populations in 1988. There is, however, recent evidence that this number was overestimated because of the previous use of line transects for estimating population sizes. In 2002–2004 we surveyed 34 previously known local populations in patches of variable size across half of its Spanish distribution. We found 13 (38%) local populations to be extinct, and a total of only 283–339 territories in 17 of the extant populations, seven of which held <5 territories. This census contrasts dramatically with the estimate of c. 3,000 pairs in the same populations in the 1980s. We estimate that the present Spanish population is c. 1,300 pairs. The discrepancy between this and earlier estimates is partly but not entirely due to previous overestimations. Habitat loss due to ploughing, and possibly habitat degradation and the resulting stochastic extinction of small and isolated populations, have contributed to the species' decline. Urgent research is needed to design and manage an adequate network of steppe patches that will ensure the long-term existence of this species. We recommend that Dupont's lark be categorized on the IUCN Red List as Endangered, both globally and nationally within Spain.

Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative eff ects of feather mites on their hosts and others reporting positive or no eff ects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing-dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). Th e overall eff ect size was only slightly positive (r ϭ 0.066). Th e eff ect of feather mite abundance explained Ͻ 10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefi t from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefi t from the presence of feather mites.