Influences of agricultural land-use and habitat modification on the breeding biology and conservation of collared pratincoles Glareola pratincola in SW Spain

1. The marshes of the Guadalquivir river and other wetlands in southwest Spain (study area) have been widely reclaimed for agriculture. One of the bird species affected by this land-use policy is the Collared pratincole Glareola pratincola. Since reclamation started, there has been a general decline of the population in the study area. 2. Collared pratincoles in the study area use marshland and farmland habitats for breeding with approximately half the population in each. However, marshland availability is only 3% of that of farmland. Colonies in farmland are found mostly in cotton fields. 3. Collared pratincoles chose marshland to breed. Here low vegetation cover and dry soil are important for settlement. In farmland, low vegetation cover, dry soil and flat terrain are important factors. Changes in crops affect pratincole colony location from year to year, but they tend to stay in the same areas. 4. Nest-site selection is not determined by the proximity of tussocks or the height of these. Hoof prints or cow-dung are not selected as nest sites, most of the nests being laid on scrapes on dry mud. In farmland, more nests are laid on plant rows than between them. This is important for their survival when work in the field takes place. 5. Colonies in marshland and farmland were of similar size and held similar number of pratincoles. Clutch size and mean clutch weight did not differ between the main study colonies (marshland and farmland), but mean clutch volume did. Eggs were bigger in the marshland colony. No difference between years was found for any of these variables. 6. Pratincoles feed mainly on insects captured in the air. They mainly use marshes and reeds for feeding. Food availability in these is higher than in crops. Crops, except cereals, are hardly used for feeding. Food availability in crops (non cereals) was also lower. 7. During the chick-rearing period adults tend to feed in the colony or nearby. Before and after this period, they often move to areas of marshes and reeds where they feed in groups. 8. Daily activity is highly influenced by insect activity and, therefore, by the weather conditions. Pratincole feeding density decreases on rainy, windy and cloudy days. In general, their activity increases through the morning up to early afternoon, and decreases after that. At certain places, activity at dawn and dusk has also been recorded. 9. Food availability in different habitats in the study area was studied with pit-fall and sticky-traps. The most trapped taxa were Coleoptera and Hemiptera. These were also the most represented taxa in chick faeces. 10. Predation of eggs in the study colonies in both types of habitat was negligible. Most clutch losses in marshland were due to abandonment and in farmland to the effect of machinery working in the field. Altogether, hatching success was high in marshland (73%-91%) and low in farmland (12%-35%). It was not possible to measure fledging success due to the difficulty in locating chicks after hatching. Different methods were tried without success. 11. This study presents data only on first clutches as it was not possible to locate replacement ones. Therefore, it is not known to what extent these make up for the loss of pratincoles first clutches. However, it is unlikely that hatching success in replacement clutches will be any higher than for the first ones since agricultural activity tends to increase rather than decrease as the season progresses. 12. Breeding performance in marshland and farmland was consistent between years within the same habitat except in farmland in 1993 when, because of an exceptional lack of water much of the farmland was not cultivated or crops were left abandoned. This allowed pratincoles to achieve a higher hatching success than in normal years in this habitat. 13. Different hypotheses to explain why pratincoles keep breeding in farmland (lower breeding performance) are discussed. Lack of marshland habitat and colony-site fidelity may have an influence on this. 14. Chicks from marshland and farmland colonies in the Guadalquivir marshes area were growing similarly. There were no differences between habitat or years. Chicks were being fed the same number of times and their diet was similar. Adult attendance did not differ either. Food does not seem to be a constraint on chick production. (Abstract shortened by ProQuest.).