Partial meso-mammal predator removal positively affects northern bobwhite reproduction

Abstract

Perceived changes in predator-prey dynamics along with documented declines of northern bobwhite Colinus virginianus have created a renewed interest from biologists and managers about the role meso-mammals play in shaping bobwhite population trajectories. Therefore, we evaluated the efficacy of meso-mammal trap and removal (MMTR) at reducing meso-mammal activity and increasing bobwhite reproductive success; thus testing the predation limitation hypothesis. During 1999-2006, we monitored bobwhite reproduction on 11 sites in three states across the southeastern United States. Combined, there were 37 site-year combinations when MMTR occurred and 20 combinations when it did not occur. We conducted 57 predator surveys and calculated an index of meso-mammal activity (i.e. predator index), for each site, as the average number of station visits per night by raccoons Procyon lotor, nine-banded armadillos Dasypus novemcinctus, Virginia opossums Didelphis virginiana, bobcats Lynx rufus and foxes Vulpes vulpes, Urocyon cinereoargenteus. The average predator index (predator visits per trap night) across sites was 0.13. We collected bobwhite reproductive information from a total of 3935 radio-tagged bobwhites resulting in 2499 nests. We used generalized linear mixed models to evaluate the relationships between MMTR, predator activity, and bobwhite reproduction. The mean predator index for non-trapped sites was 0.21 (95% CLs: 0.18, 0.24) compared to 0.10 (95% CL: 0.07, 0.13) for trapped sites. Bobwhite nests were 1.33 times (Odds ratio, 95% CL: 1.09, 1.62) more likely to be successful on trapped sites than non-trapped sites. Meso-mammal trap and removal had a positive effect on nests per hen (βtrapped= 0.25 ± 0.06; 95% CL: 0.13, 0.37), broods per hen (βtrapped = 0.37 ± 0.08; 95% CL: 0.21, 0.53), and chicks per hen (βtrapped = 1.09 ± 0.52; 95% CL: 0.07, 2.11). Our results show that MMTR reduces meso-mammal activity and positively affects bobwhite reproduction.