The unexplored maternity dens survey of the polar bear (Ursus maritimus) on Wrangel and Herald islands in 1982

Abstract

In March–May 1982, a local expedition worked in the Arctic, in the east of Wrangel Island (WI) and Herald Island (HI), to carry out a survey of polar bear dens. The results of that expedition have not been published. The author has found a copy manuscript of the expedition diary and has highlighted the key results. For two months, five ex-plorers had been surveying the area and found 139 dens and sighted 57 bears (♀ad + juv). The average number of offspring (ANO) was 1.43 on WI and 1.86 on HI. The number of successful offspring on WI usually was one or two cubs, or even three on HI. Based on the available sample (n=44) it was shown that when taking into account the survey data of cub traces in calculations of ANO (on WI), the obtained results do not differ notable. The time that lasted from the date of the opening of the den to the date of the final leave of the den by females (with or without the young) was 4 to 14 days, but most often 6 days. The highest frequency of den opening was noted on 27–28 March. Four cases of death of cubs, including a newborn, were recorded. The fate of 43 dens was monitored and measurements of 11 dens were taken. Two unusual dens were found: one with a very complex corridor and another one with a 4.5 m long vertical tunnel. Simplified 3D models of dens were given in the article for the first time proving that linear measurements practiced by researchers give a primitive picture of the den structure. After leaving the maternity den, the female can build temporary, simple shelter for herself and the young. During 1964–2020, dens were found on these islands only on the ground, and in 1980 the author found several dens on the sea, among ridges of pressured ice. The article is amended by the author’s estimations regarding the place of the polar bear in ecologi-cal pyramid of those islands. Recommendations are given for the improvement of polar bear survey techniques. The publication of a Ukrainian language article on the biology of U. maritimus is rare for the school of Ukrainian mammalogists and is of clear enlightening importance for scientists, lecturers, students, Wikipedia editors, and oth-ers, as well as a contribution of the author to the Ukrainian body of literature on the animal world of the Arctic.