A test for effects of radio-tagging on survival and movements of small birds

Abstract

There is little experience and scant data about possible adverse effects of radio-tagging on birds of less than 20 g. To quantify possible effects, we analysed the survival rate and movements of 221 radio-tagged and 121 colour-marked great tit Parus major and coal tit P. ater fledglings. In these species, post-fledging survival is strongly related to the physical condition of juveniles, so that the additional load of a transmitter might have an adverse effect on the bird’s energetics and body condition, and therefore affect the survival rate. Cormack-JollySeber models confirmed the effect of fledging weight on juvenile mortality. In neither weight class, however, did the survival rate of birds equipped with a 0.5 g transmitter differ from the control-group of untagged individuals. Radio-tagged birds did not disappear earlier from tit families than untagged individuals, which indicates that tagged birds were not more vulnerable to predation or accidents than their untagged siblings. We found no effect of the number of transmitters deployed per family on the distances covered per 5-min interval. Although these results are limited to survival and selected parameters of behaviour, we conclude that the additional load of 2.4–3.3 % of the birds’ body mass in great tits and 4.2–5.8 % in coal tits did not significantly affect the birds’ body condition, manoeuvrability or range use.