Tesi di dottorato di ricerca
Stopover ecology and migratory orientation of shorebirds (Aves, Charadriiformes) in a coastal Tyrrhenian wetland
Settore scientifico disciplinare
Corso di studi
SCIENZE BIOLOGICHE E MOLECOLARI
tutor Prof. Baldaccini, Natale Emilio
relatore Dott. Giunchi, Dimitri
relatore Dott. Giunchi, Dimitri
- migratory restlessness
Data inizio appello
Data di rilascio
Abstract<br><br>The knowledge of individual and environmental parameters affecting stopover length in shorebirds is important for the conservation and management of species and environments often seriously threatened, such as Mediterranean wetlands. The role of physical and habitat conditions in determining the length of stay is not always easy to study in the field, since many external factors (i.e.: atmospheric conditions) may influence the decision to leave a stopover site. Several recent studies on Passeriformes show that applying both field and laboratory research may help to understand factors affecting stopover length. Some of these studies demonstrated that the amount of migratory restlessness in passerines can be considered a good proxy for quantifying the willingness to depart from a refuelling site. Even if shorebirds have proved to be good models for laboratory research, the only papers regarding migratory restlessness in this group concern studies on orientation mechanisms, which are mainly aimed at showing their use of magnetic compass.<br>The present work aims: (1) to investigate the spring migration ecology of Wood sandpipers (Tringa glareola) and Curlew sandpipers (Calidris ferruginea) at a Tyrrhenian stopover site, (2) to study the presence of migratory restlessness in shorebirds and its relation with body conditions and stopover length by using spring migrating Wood sandpiper as a model, (3) to develop a method useful to effectively study orientation in caged shorebirds and (4) to investigate the hierarchal relationships among compass references used by shorebirds by means of cue conflict experiments performed in Curlew sandpipers and Dunlins (Calidris alpina).<br>Curlew and Wood sandpipers are quite common as staging species during spring migration, but they seem to follow two different migration strategies. Our data show that Curlew sandpipers arrive in the area in fat conditions and ready to depart Northbound, whereas Wood sandpipers are likely to land in the study site in depleted condition, probably just after a no-stop flight over the Mediterranean Sea.<br>Our study is the first one to employ axial accelerometer to measure migratory restlessness in birds. Despite this method proved to be effective in recording Wood sandpipers activity, we failed to found any relationship among their stopover length, body conditions and nocturnal activity. The level of nocturnal activity was overall low, whereas a peak in activity was registered during sunset period. This twilight activity was oriented, and its level varied significantly according to the amount of food available in captivity, similarly to the migratory restlessness recorded in Passeriformes.<br>In order to study orientation, we developed a new method for recording directional preferences in captive shorebirds consisting in the use of infrared video recording cameras placed at the bottom of a transparent modified Emlen funnel. This method proved to be successful in recording the preference and the activity of tested species, representing a significant improvement with respect to previous methodologies used for shorebirds. Cue conflicts revealed that Curled sandpipers and Dunlins are able to use the geomagnetic field to orientate under a simulated overcast sky. Tested birds seem not to recalibrate their magnetic compass on visual cues after the cue-conflict. Our data, however, indicate that they do not completely disregard the information derived from celestial cues.<br>Data collected in the present work represent the first attempt to investigate the presence and the characteristics of migratory restlessness in shorebirds. Furthermore this is one of the few experimental studies on migratory orientation of Charadriiformes and, in particular, on the hierarchical relationships between the different compasses used by these birds during their extensive migratory movements.
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