The Eurasian stone curlew (Burhinus oedicnemus) is classified as a species of conservation concern in Europe, mainly due to its population decline which has been caused by the loss and fragmentation of reproductive habitat. Current availability of detailed information on its biology is quite poor and is mostly limited to studies on English populations; these breed on the northern edge of the European range and use quite different habitats from the Mediterranean populations.
The aim of this thesis was to investigate some aspects of the ecology and behaviour of stone curlews breeding in a poorly known habitat, i.e. river, which is an important breeding habitat for Italian populations. In particular, the stone curlew population nesting in the Parco Regionale Fluviale del Taro (Parma, Italy) was studied; this area hosts one of the largest populations in continental Italy. Hatching success, moult strategies during the breeding season and the spatial behaviour of the species were all investigated.
Since the study population primarily breeds in the riverbed, the influence of the river dynamic on hatching success was examined. Nests were monitored periodically, inter alia, using temperature loggers, which limited disturbance by significantly reducing the number of visits. Furthermore, the availability of data on the precise failure date of nests improved the estimates of survival rate and provided some useful insights into the possible causes of failure. Parameters such as mean temperature and the amount of rainfall during the breeding season did not have any effect on hatching success. However, nest survival was lower in years not preceded by significant autumn-winter river flows. This suggests that hatching success could be at least partially related to the river dynamic, which determines the characteristics of nest sites by removing vegetation on the riverbed and by reshaping the river course. The open habitat around nests could limit predation risk, by increasing the detection probability of terrestrial predators and by reducing the number of perches used by corvids to prey on eggs.
One of the most interesting aspects regarding moult strategies was the extensive overlap between the moult and breeding season. Primary moult in the study population was very slow, starting at the beginning of the breeding season (May) and ending in October. Secondary moult was much more irregular and, even though it started when birds were still nesting, most of the secondaries were replaced during the post-reproductive period. Secondary moult was not completed within a single moult cycle: innermost and outermost secondaries were more likely to be shed than those at the centre of this tract and juvenile secondaries were not shed during the first year. On the whole, the observed combination of early commencement of wing moult and extensive overlap between moult and the breeding season is relatively uncommon among waders and, more generally, among other avian species breeding in temperate regions. This could be interpreted as a strategy to maximize hatching success (which was quite low in the study area) through re-nesting potential, i.e. by spreading the cost of moult over a prolonged time period. The results of a comparative analysis performed among wader species of the Palaearctic area were consistent with this hypothesis: species with a prolonged breeding season also showed considerable overlap between moult and the breeding season.
In relation to stone curlew spatial behaviour, attention was focused on the analysis of the environmental features that influence the bird’s feeding choice and on the interaction between birds and human activities (chiefly agricultural) in the study area. During the day birds concentrated their activity almost exclusively in the riverbed, whilst at night they regularly commuted from breeding sites to feeding areas (mostly farmland) a few kilometres away. In these areas, stone curlews showed a clear preference for recently mown crops (mainly forage and wheat) and piles of farmyard manure. Habitat preference is closely linked to the predominant agricultural activity of the study area, namely a high density of farms producing ‘Parmigiano-Reggiano’. This provides a wide range of suitable foraging sites close to nesting territories. The ability of stone curlew to breed successfully in fairly intensive farmland, could help to explain the high density of breeding pairs recorded in the study area. We propose that the conservation of stone curlew in this habitat could potentially be achieved only by a synergistic management of both natural and agricultural habitats.