Using Anal Gland Secretion to Determine Sex in Beaver

Abstract

Controlling beaver (Castor canadensis) populations is a problematic issue for wildlife managers in North America. Management of beaver can be facilitated by determining sex ratio of a population, but this requires ready identification of gender for live and harvested beaver. We developed a technique using color and viscosity of anal gland secretion (AGS) to identify gender of beaver. Inexperienced volunteers inspected AGS from beaver in 3 regions of New York. Using AGS collected and stored in glass vials, 4 volunteers correctly identified sex of 24 beaver (16 M, 8 F) livetrapped during spring 1992; 2 additional pairs of volunteers correctly discriminated 45 beaver (21 M, 24 F) livetrapped in spring 1993 and 1994. Using fresh AGS viewed in the field, 1 volunteer correctly discerned 25 beaver (15 M, 10 F) caught in October 1993; and 2 volunteers distinguished sex of 5 beaver (3 M, 2 F) captured in November 1992 without error. Male AGS was Kraft brown (P55, Marker color system) to sepia (P56) and viscous (490-507 centipoise [cP] at 25.8 C and 60 rpm, Brookfield DV-11 + viscometer), while female secretion was pale to medium olive (P34, P39) or warm gray (P191), less viscous (4-28.7 cP, 23-25.4 C, 50 or 100 rpm) and flowed more (P < 0.001) than male AGS. Secretion color and viscosity were discriminating means of distinguishing the sexes in the field.