Abstract
Among birds, breeding numbers are mainly limited by two resources of major importance: food supply and nest-site availability. Here, we investigated how differences in land-use and nest-site availability affected the foraging behaviour, breeding success and population trends of the colonial cavity-dependent lesser kestrel Falco naumanni inhabiting two protected areas. Both areas were provided with artificial nests to increase nest-site availability. The first area is a pseudo-steppe characterized by traditional extensive cereal cultivation, whereas the second area is a previous agricultural zone now abandoned or replaced by forested areas. In both areas, lesser kestrels selected extensive agricultural habitats, such as fallows and cereal fields, and avoided scrubland and forests. In the second area, tracked birds from one colony travelled significantly farther distances (6.2 km ±1.7 vs. 1.8 km ±0.4 and 1.9 km ±0.6) and had significant larger foraging-ranges (144 km2 vs. 18.8 and 14.8 km2) when compared to the birds of two colonies in the extensive agricultural area. Longer foraging trips were reflected in lower chick feeding rates, lower fledging success and reduced chick fitness. Availability and occupation of artificial nests was high in both areas but population followed opposite trends, with a positive increment recorded exclusively in the first area with a large proportion of agricultural areas. Progressive habitat loss around the studied colony in the second area (suitable habitat decreased from 32% in 1990 to only 7% in 2002) is likely the main driver of the recorded population decline and suggests that the effectiveness of bird species conservation based on nest-site provisioning is highly constrained by habitat quality in the surrounding areas. Therefore, the conservation of cavity-dependent species may be enhanced firstly by finding the best areas of remaining habitat and secondly by increasing the carrying capacity of high-quality habitat areas through safe nest-site provisioning.
Highlights
Maintaining or increasing the population numbers of endangered species requires the identification of the limiting factors of population sizes, without which the management of any species population is likely to be unpredictable [1]
The carrying capacity of any environment for breeding populations is usually set by two resources of major importance - nest-sites and food - and whichever is in shortest supply can limit the number of breeding pairs [2]
Since 1996, the occupation of provisioning of artificial nest-sites allowed the rapid and significant increase of colony size (Fig. 1)
Summary
Maintaining or increasing the population numbers of endangered species requires the identification of the limiting factors of population sizes, without which the management of any species population is likely to be unpredictable [1]. Within their habitats, most bird populations are naturally limited by the availability of food, safe nest-sites, predation, competition and diseases [2]. The interaction between food and nest-site availability seems to play a decisive role during the breeding season: the distance that birds travel between nest-sites and foraging areas seems to depend largely on food availability and constitutes an important component of time-energy budgets [14,15,16,17]. The energetic costs of nesting a long distance from foraging grounds tend to be inefficient and may have ecological consequences resulting in poor breeding success [6,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
