Inter and intra-population variability of the migratory behaviour of a short-distance partial migrant, the Eurasian Stone-curlew Burhinus oedicnemus (Charadriiformes, Burhinidae)

Migratory behaviour in birds shows a remarkable variability at species, population and individual levels. Short-distance migrants often adopt a partial migratory strategy and tend to have a flexible migration schedule that allows a more effective response to extreme environmental variations. Weather seasonality and environmental heterogeneity have been reported as significant factors in the diversification of migratory behaviour for Mediterranean migrants, but relatively few studies investigated the migration patterns of non-passerine birds migrating within the Mediterranean basin. In this study, we investigated the migratory strategy of 40 Eurasian Stone-curlews Burhinus oedicnemus tagged with geolocators and GPS-GSM tags and belonging to continental and Mediterranean populations of the Italian peninsula. The proportion of migrants was higher in continental populations, but we observed a significant variability also within Mediterranean populations. All birds spent the winter within the Mediterranean basin. Continental Stone-curlews departed earlier in spring and later in autumn and covered longer distances than those from Mediterranean areas. The speed of migration did not change between seasons for continental birds, while Mediterranean individuals migrated faster in spring. The likelihood of departure for autumn migration of GPS-tagged birds increased when temperatures were near or below 0 °C suggesting that Stone-curlews tend to delay departure until weather conditions worsen abruptly. As a consequence of global warming in the Mediterranean, the frequency of migratory birds in the considered populations might decrease in the near future. This could affect the distribution of species throughout the year and should be taken into account when targeting conservation measures

Migratory strategies of Stone-curlew Burhinus oedicnemus populations breeding in continental and Mediterranean regions of Italy

Bird migration shows a great variability between species, populations and individuals, with multiple factors affecting its mechanisms. Routes and timings are endogenously regulated; however, birds should also consider environmental cues to cope with the interannual climatic variability. Migratory tendency varies both between populations occupying different geographical ranges and within the same population (i.e. partial migration). Furthermore, it is known the climatic influence on migratory phenologies, especially among short-distance migrants. We aimed to describe the migratory behavior of the partial migrant Eurasian stone-curlew Burhinus oedicnemus, by investigating different populations breeding in continental and Mediterranean Italy. GSM/GPS data were used to analyse the migratory tendency and to compare the time of departure, migratory speed and length among areas and seasons. Moreover, the possible role of exogenous factors on autumn departure time was investigated. Stone-curlews traveled short distance in a few days. Routes, wintering sites and autumn departures showed a large inter-individual variability. Departure probability appeared to increase with conditions hindering both foraging on soil invertebrates and a cheap bird thermoregulation (low temperature), and was probably influenced by those favoring weather (high atmospheric pressure). This study provides new data regarding the stone-curlew migratory strategies and could be useful for predicting how the species will react to the ongoing climate change

First Chemical–Physical Measurements by Multi-Parameter Probe in the Blue Hole of Faanu Madugau (Ari Atoll, the Maldives)

Blue holes are submarine karst cavities with chemical and physical characteristics of the water column completely different from those in the surrounding environment. In this study a multi-parameter probe was used, for the first time, to characterise the water column of the Blue Hole of Faanu Madugau (Ari Atoll, Maldives, 3 degrees 55.799 ' E 72 degrees 56.469 ' N), the only blue hole described in the Indian Ocean up to date. Measurements of the temperature, salinity, dissolved oxygen, turbidity, chlorophyll-alpha, photosynthetically active radiation, potential density, pH, and H2S were obtained with a high detail. Three distinct physical-chemical layers were identified from the surface up to 70 m depth. An intermediate and turbid layer, located between 40 m and 46 m depth, sharply separates the upper layer displaying water characteristics equal to those of the outside environment from the deep and more characteristic layer of the blue hole, where a unique environment can be observed. Waters are oxygenated, warm, and rich in chlorophyll-alpha in the upper layer, whilst waters are anoxic, colder, denser, and completely dark, with low pH values and high H2S content in the deep layer. The Blue Hole of the Maldives represents an extreme environment from a geological, oceanographic, biological, and ecological point of view. Further investigations will be thus required to understand the origin of the Blue Hole waters, the mechanisms that keep it isolated from the external environment, the influence of weather and marine forcing on it, and how climate change may impact it