SEASONAL AND CIRCADIAN ACTIVITY AND SPATIAL EXTENT OF WHITE-BACKED HOG-NOSED SKUNK (CONEPATUS LEUCONOTUS) ALONG THE COLORADO RIVER THROUGH THE GRAND CANYON

Relatively little is known about the ecology of the white-backed hog-nosed skunk (Conepatus leuconotus) in the United States. Between June 2015 and September 2016, we used camera traps to document the occurrence and seasonal and circadian activity of white-backed hog-nosed skunks at 21 camera trap stations along the Colorado River through Grand Canyon National Park, Arizona, USA. We detected a minimum of 19 individual skunks, including one mother-offspring pair, at camera traps across a 55-mi (88-km) stretch of river. Seasonal activity, measured as mean number of photographs per night, was lowest in December when average air temperatures were also lowest (108C), increased in the breeding season between January and March, peaking in February, fell in April and May, and then rose to the highest levels in the summer months of June to September. Circadian activity was primarily nocturnal and appeared to be bimodal with an earlier peak circa 2200 h and a later peak centered on 0200 h. Nocturnal activity was not associated with lunar phase, and skunks were not more active on warmer nights during winter. Given that there was no record of white-backed hog-nosed skunks in the Grand Canyon prior to 2012, we hypothesize that increases in shoreline vegetation since the completion of the Glen Canyon Dam in 1963 has increased invertebrate prey availability, allowing white-backed hog-nosed skunks to colonize the lower reaches of the Colorado River within Grand Canyon National Park.