Fecal DNA, hormones, and pellet morphometrics as a noninvasive method to estimate age class: an application to wild populations of Central Mountain and Boreal woodland caribou (Rangifertaranduscaribou)

Abstract

Determining age structure of populations is a valuable parameter in wildlife management, but is often difficult to obtain. Here, we tested a noninvasive method via fecal DNA, hormones, and pellet morphometrics to distinguish calf from adult in Central Mountain and Boreal woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) populations. Annual surveys of fall-sampled Central Mountain caribou were done in Jasper National Park, Alberta, between 2006 and 2011 and winter-sampled Boreal caribou were surveyed in the North Interlake area, Manitoba, between 2004 and 2010. Samples were amplified at 10 microsatellite loci to identify unique individuals and capture histories were used to identify putative calves and adults. Fecal pellets were measured for length, width, depth, dry mass, and analyzed for progesterone, estrogen, and testosterone concentrations. Results showed significant differences in fecal pellet size between putative calves and adults for both sexes and populations–seasons. Progesterone concentration was significantly higher in Jasper–fall and North Interlake–winter adult females. Testosterone was significantly higher in Jasper–fall adult males. North Interlake–winter males exhibited no significant difference in hormone concentrations between age classes. When applied to the entire Jasper data set, 98% of females and 88% of males were assigned to an age class. This study illustrates the possibilities of using noninvasive methods to determine an age class in wild ungulate populations.