Effect of Grazing on Density and Breeding Success

of Lesser and Eurasian Kestrels

Report to the National Birds of Prey Trust

2006

As expected, the highest level of organophosphorus contamination (lowest level of acetylcholinesterase) was observed in an agricultural habitiat (Fuente de Santa Cruz) where the cereal was collected during 2005. In the other agricultural area (Los Monegros) farming activities were not carried out during the studied breeding season due to drought suffered in the region. Acetylcholinesterase values in this area were similar to those found in grassland habitats.

In relation to nutritional status, no clear associations were found between albumin and acetylcholinesterase levels indicating that the physiological incorporation of contaminants do not affect the nutritional status in both kestrel species. Similar results in relation with the ratio albumin/globulin also indicates that organophosphorus contamination is not associated with clinical state in kestrels. Gamma-globulins levels showed however that kestrels from south-west Spain were in worst health status than in the other populations, probably due to nestlings of this zone had a infection. This requires further research.

One unique measure, like acetylcholinesterase levels is not sufficient to determine the individual health state, because we obtained opposite results between acetylcholinesterase levels, which indicate organophosphorus contamination levels and albumin and ratio albumin/globulin, which indicates nutritional and clinical state. Eurasian kestrels showed lower differences in the studied variables among localities than Lesser kestrels, probably due to the differences in alimentary composition between species, principally insects in the Lesser kestrel and mixed (insects, amphibians, reptiles small bird and small mammals) in the Eurasian kestrel.

Finally, although our results are preliminary, they point out to an absence of relationships between levels of contamination and nutritional-health status in kestrels. This has important implications in terms of the conservation of these threatened species, and our results show that to evaluate correctly the health status of kestrel populations is necessarily measured more than one health state indicator.