Effects of radiotransmitters on survival and reproductive success of gray partridge

Because of the recent decline in gray partridge (Perdix perdix) populations in northern France, we conducted a field study in 1995-97 by using radiotelemetry to examine mortality causes. We investigated the effects of radiotransmitters on survival, reproductive success, and body mass of gray partridge. We captured 260 hens in spring 1995, 99 in autumn 1995, and 358 in spring 1996 and tagged them with a 10-g necklace radiotransmitter. We found no effects of radiotags on survival (P = 0.101), reproductive success (P = 0.375), and body mass (P = 0.990) in spring 1995. In contrast, adverse effects were observed in spring 1996 on survival (P < 0.001), reproductive success (P = 0.006), and body mass (P = 0.013). The postrelease effect on survival observed in spring 1996 varied among populations (P < 0.001), between radio types (P = 0.036), and with regard to body mass at time of capture (P = 0.046). The difference observed between years and across study areas were correlated to weather and predator abundance but not to habitat features we measured. Our findings suggest that radiotelemetry data must be carefully interpreted with regard to potential radiotag effects, all the more that these effects are influenced by environmental conditions.