Increasing nest site availability for lesser kestrel Falco naumanni in Castro Verde Special Protection Area, Beja, Portugal
Franco A.M.A., Marques J.T. & Sutherland W.J. (2005) Is nest site availability limiting lesser kestrel populations? a multiple scale approach. Ibis, 147, 657-666.
Background
Over the last fifty years lesser kestrels Falco naumanni have suffered a large population decline throughout their European range. The main reasons for this decline have been attributed to loss of foraging habitat (Donazar et al. 1993). In Portugal, loss of breeding sites was also identified as one important cause of decline. Lesser kestrels do not build their own nest, they breed in existing natural cavities in cliffs, and in humanized landscapes in cavities in the roof or walls of old buildings such as churches, monasteries or castles. This case study outlines the construction and use of strutures especially built as breeding sites for lesser kestrels in southern Portugal.
Action
Study area: In the Castro Verde Special Protection Area, situated in the south of Portugal, farmers can voluntarily adopt agri-environmental measures in order to help them to continue using traditional farming techniques and in this way contribute to the maintenance of the pseudo-steppe habitat that is extremely important as foraging and breeding grounds for several endangered steppe bird species, including the lesser kestrel.
Construction of breeding towers: From 1995 to 1999 two European Union LIFE-nature projects were implemented aiming to contribute to the conservation of steppe birds. In light of a lack of suitable nest sites, two new tower-like structures were built with cavities (17 and 19 each) designed especially for lesser kestrels. The first tower was completed in 1997 and the second in 1999. The new towers were not occupied by lesser kestrels until 2001, when two nest boxes were placed on top of each and immediately occupied, however the cavities remained unused. The question was asked, if lesser kestrels did not avoid the breeding towers and readily used the nest boxes, what was wrong with the cavities designed as nest sites?
Nest cavity research: During 2001, a research project was carried out comparing utilised cavities in 12 colonies located in rural buildings with non-utilized ones located in the same rural buildings. The results suggested that nest holes were larger, longer, higher and (of course) older than the unoccupied cavities in the towers. A typical nest cavity was approximately 29–30 cm long, 300–340 cm high and had an inner chamber 16.5–18 cm wide. When compared with the dimensions of the cavities provided in the towers the only difference was the absence of an inner cavity.
Consequences
In view of the research findings, the cavities in the nest towers were amended accordingly - the walls of the cavities were destroyed and enlarged to provide the inner cavity that was missing. In the following breeding season (2002) after these changes had been made to the cavity structure, the two towers were occupied by the first pairs of cavity-nesting lesser kestrels, with three pairs breeding successfully. In 2003, three of 17 cavities (18%) in tower 1, and six of 19 (32%) in tower 2 were occupied by breeding lesser kestrels. A few other species were also attracted to and bred in the towers, including common kestrel Falco tinnunculus, roller Coracias garrulus, barn owl Tyto alba and jackdaw Corvus monedula (see Table 1 attached, extracted from Catry et al. 2004).
In 2003 a new EU-LIFE project especially dedicated to the conservation of lesser kestrels in Portugal was approved (2003-2005), new nests were created in the walls of existing colonies, additional nest boxes put up and three new 'breeding walls' were built. These new structures have now been completed and provide cavity nest sites with the optimal dimensions (see Table 1). For more details and photos see www.lpn.pt
References
Birdlife International (2004) Birds in Europe: population estimates, threats and conservation status, Cambridge, UK.
Catry I., Reis S., Alcazar R., Cordeiro A., Rocha P. & Franco A. (2004) Será o aumento da disponibilidade de locais de nidificação uma medida de gestão eficaz para a recuperação do francelho em Portugal? Airo, 14, 21-28.
Donazar J.A., Negro J.J. & Hiraldo F. (1993) Foraging habitat selection, land-use changes and population decline in the lesser kestrel Falco naumanni. Journal of Applied Ecology, 30, 515-522.
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