Do radio collars influence mortality and reproduction? A case with ring-necked pheasants (Phasianus colchicus) in Central Italy

The effect of radio transmitters on bird survival and reproduction has been explored in the literature, and contradictory results were found. Using the Kaplan-Meier method, we estimated the mortality of female ring-necked pheasants (Phasianus colchicus) in relation to radio load (percentage of total body mass). Low-load birds showed a higher survival, particularly after 2-3 months from release, thus excluding short-term effects of handling and adjusting to packages. Reproductive success was higher for birds with low loads, but the effect was less clear. The results were not influenced by age or body mass. As a rule of thumb, using radio packages lighter than 1.5% of the body mass can be considered safe for pheasants, whereas loads above 2% may have adverse effects.