A monitoring program for Patagonian foxes based on power analysis

ALEJANDRO TRAVINI; ALEJANDRO RODRÍGUEZ; DIEGO PROCOPIO; SONIA C. ZAPATA; JUAN IGNACIO ZANÓN MARTÍNEZ; ROLANDO MARTÍNEZ-PECK

EUROPEAN JOURNAL OF WILDLIFE RESEARCH

SPRINGER

Año: 2010 vol. 56 p. 276 - 286

1612-4642

Culpeo fox (Pseudalopex culpaeus) and gray fox (Pseudalopex griseus) are heavily culled in Patagonia. Fox populations seem to persist thanks to spatial refuges from which hunted areas are repopulated, following a source?sink dynamics. Sustainable use of Patagonian foxes warrants the design of a monitoring program in nature reserves and areas subjected to predator control. During 7 years, we used visitation indices to bait stations in a national park and neighboring sheep ranches of southern Argentina. We operated bait stations during three consecutive nights and calculated seven indices of relative abundance. For each fox species, we compared the power of different monitoring designs and scenarios that combined visitation indices, effort (number of bait station lines andsurvey frequency) while controlling for type I error, and magnitude of population change during a given period. We looked at the combinations that produced high power (β≤0.24). The operation of bait stations during severalnights markedly increased statistical power. Index 7 (recording visits 72 h after activation) exhibited the lowest variation and improved expected power to detect a population trend. Both fox species could be monitored simultaneously, with power >0.76 in the short term (5 years), activating 24 bait station lines. We conclude that monitoring programs for culpeo fox and gray fox based on bait stations are able to detect marked declines but are less useful to reliably detect moderate increases in abundance, especially in sheep ranches.