Scent marking and responses to male castor fluid by beavers

Abstract

Beavers (Castor canadensis) live in family units and construct mud mounds marked with urine-based castoreum, at least in part as territorial advertisement. Marking varies in degree by season and in a density-dependent fashion among sites (families). I examined predictions of a territorial hypothesis for scent marking based on the ability of beavers to detect and discriminate scents and whether signs of intrusion stimulated mound building. Intruders could be adjacent adult territory holders (neighbors), more distant adults (nonneighbors), or offspring of either (juveniles). I determined the extent of investigatory responses and number of additional mounds built by beavers in response to beaver scent mounds (BSM) and to castor fluid from adult and juvenile males placed on human-made experimental scent mounds (ESM) in the field. Beavers distinguished scented from unscented mounds and discriminated among at least castor-fluid scents from family, neighbor, and nonneighbor adult males. Adult beavers exhibited the least interest in castor fluid from their own offspring. Beavers did not build more mounds in response to any treatment, but scented ESMs were over marked more often than family BSMs or blanks. Unless intrusion rates are very high, intrusion alone cannot explain differential scent mounding among sites. However, anticipated intrusion and site quality may establish initial mounding behavior that is modified by intrusion and subsequent over marking.