Survival Rates of Young Magpies Pica pica in a Mountain Population of Eastern Spain

pg(s) 63–68

The aim of this study was to estimate the survival of young Magpies between fledging and the next breeding season and to identify some of the factors affecting it. A total of 50 nestlings were colour-ringed in two breeding seasons in the valley of the Pitarque River (Teruel, E Spain), and were monitored weekly until May of the following year. 59 nestlings were also colour-ringed in two nearby localities (4–5 km) to detect possible dispersal to and from our study area. Mark-recapture analyses were used to estimate weekly survival, which was assumed to be constant for periods of four weeks in order to reduce the number of parameters. Models with the effect of time, age class, season and year were fitted, and the best models were selected using quasi-likelihood Akaike's Information Criterion adjusted for small sample sizes (QAICC???). The best three models included seasonal variation in survival, and the second and third models also selected the effect of age class. The seasonal variation in the survival of young Magpies exhibited two critical moments: firstly, on becoming independent of the parent birds (August—September), and secondly, when individuals abandoned the communal roost and started to establish their own territories (February—March). The weight of 14-day-old nestlings positively affected survival until 4 and 6 months after leaving the nest. No evidence for dispersal was found; this supports the view that survival does indeed decrease in the cited periods, possibly because of the increased risk of predation.