关键词: 黑熊, 棕熊, 年龄构成, 性比, 繁殖

Abstract: The age compositions,sex ratios, reproductions and the relationships between the bacular length and the age of black bears (Selenarctos thibetanus ussuricus) and brown ones (Ursus arctos lasiotus) in Heilongjiang Province were studied from 1983 to 1985.A total of 199 specimens of bears, 112 black and 87 brown, killed between November 1983 and March 1984,were examined.Unfortunately, these specimens were damaged so seriously that only 65 skulls,31 of black bears'and 34 of brown bears',and 31 bacula,15 of black bears'and 16 of brown bears', and 75 first lower premolars of black bears (34) and brown bears (41) were collected for further studies.Among the specimens the average age was 4.15 yr for black bears and 4.37 yr for brown ones; the 3-year-old made up a proportion of 44% far the former and 51.2% for the latter; the oldest aged 11 yr for the former and even older for the latter.The sex ratio of the black bears did not differ from l:l(P = 0.1) but that of the brown bears did,favoring females in the adults.There were 35.6% of the black bear females and 30.2% of the brown ones giving birth to cubs that winter. Adult female reproduction rates of 41.7% in black bears and 47.1% in the brown indicated that the mean birth intervals were about 2-3 years. The earliest age at first litters for these two species was 3.There were close nonlinear regressive relationships between the bacu-lar length and the age of these two species,and the regression equations and the correlation coefficients were as follows:Y = 58.54X^0.41,r = 0.998(for black bears) and Y = 61.38 + 104.3 logX,r = 0.997(for brown bears).The bacular lengths could be considered as an age indicator for young individuals of these two species.It was believed that the fact that much more youngers were found in these two populations in contrast with some populations in other countries was a consequence of a higher hunting pressure on them in the past few years.Some suggestions about the conservation and exploitation of bears were made in the paper.

Key words: Black bear, Selenarctos thibetanus ussuricus, Brown bear, Ursus arctos lasiotus, Age composition, Sex ratio, Reproduction