Principal Investigators:
Dr. Michael J. Conroy, Georgia Cooperative Fish & Wildlife Research Unit, D. B. Warnell School of Forest Resources, University of Georgia
Dr. Juan Carlos Senar, Musuem of Zoology, Barcelona, Spain
Funding:
North Atlantic Treaty Organization
Sex differences in survival, dispersal and movement rates are central topics in modern ecology. Capture-recapture methodology may provide a good approach for estimation of these parameters. However, biological problems are very complex, calling for the estimation of numerous parameters and the testing of multiple hypotheses. For instance, many bird populations contain a significant proportion of transient birds, and sexes and ages may differ in both dispersal and survival patterns, so that the estimation of any of these parameters necessarily needs to take into account the variation in the other factors . Any of these parameters may also differ between seasons. The biology of the species may also pose additional difficulties: for instance the sexes of juveniles of many bird species cannot be determined, but may be predicted from morphometric variables (e.g., wing length). Therefore, new capture-recapture models are needed which approach closer and closer to the complex biological reality, while still retaining parsimony.
Our objectives were to develop a capture-recapture model taking into account the above sources of variation in survival rates and sampling difficulties. Specifically, we suggest a model to handle data sets in which 1) the sex of birds cannot be determined prior to first moult, but can be predicted on the basis of body measurements, and 2) a significant portion of captured birds appear to be transients. To identify how the parameters vary across seasons, we divide the year in three periods (breeding, moulting and wintering seasons). We applied this model to The study was carried out using capture-recapture data from the Serin, a small (10g) granivorous passerine bird typical of the Mediterranean area. As in other Cardueline finches, a significant (but unknown) percentage of the population is highly mobile (i.e., transient). Serins were trapped from 1985 to 1996 at the suburban area of Barcelona (NE Spain), resulting in over 4,000 captures. We developed a complex model containing over 500 parameters, but the optimal model for estimation was based on only 46 parameters and allowed us to investigate age-, sex-, and time-specific variation in survival rates, capture probabilities, and residency parameters.
For further information contact Michael
J. Conroy