Reproduction and Denning of Black Bears in the Great Smoky Mountains

Abstract

The reproduct iv e biology and denning ecology of black bears were studied in the Great Smoky Mountains National Park and Chero kee National Forest . The majority of information was collected from 36 radio-instrumented females monitored from June 1980 to May 1982. Females entered dens from 21 Nov ember to 16 January (x=20 December, n=38), and emerged from 18 March to 4 May (x=10 April, n=41), for an av erage denning period of 113 days. Females with newborn cubs denned significantly longer (P< 0.001) than other females. Tree denning females emerged later and remained in dens longer than others. Twenty-five ground dens and 33 tree dens were examined. Significant differences (P< 0 . 005) in den utilization were observed between winters , with more tree dens being utilized during the winter of 1980-81 (79 . 3%) than in the winter of 1981-82 (34 . 5%). Females in estrus were captured from 22 June to 12 July (n=5) and 5 August to 18 August (n=3). Serum estradiol-178 concentrations in females displaying prominent signs of estrus (x= 92.3 pg/ml) were signifi cantly higher (P< 0. 001) than in females showing no signs of estrus (x=51 . 31). Serum estradiol concentrations appeared to be a more reliable indicator of estrus than vagi nal smears. The av erage age at first litter was 5 . 2 years , and the av erage i nterval between successful litters was 2 . 15 years, with iv t h e major i ty ( 11 o f 13 ) o f female s re prod u c i n g i n altern a te years. Food ava i la b i l i ty , p a rt i c ularly t h a t of h ard m a s t i n t h e fall, i n fluen ced ma ny re p r oduc t i v e parameter s , i n clud i n g m i n i mu m re produ c t i ve a g e , produ c t i v i ty , a n d c ub s urv i val . Wh i te oa k m a s t a v a i lab i l i ty demo n s tra ted t h e s t l i n e ar rela tio n s h i p ( R2=0 . 86 , P<0.0 7 2 2 ) t o t h e perce n t a g e o f female s w i t h n ewborn c u b s in w i n ter den s . L i tter s i z e s o f newborn c u b s ra n g ed from 1 t o 4 ( x= 2 . 58 , n=19 ) ; a major i ty o f l i t ters ( n=16 ) c o n t a i n ed 2 or 3 c ub s . The a v e r a g e we i g h t o f 35 newborn c u b s exam i n ed from 28 Febru ary to 19 Marc h 1982 wa s 1 . 82 kg. Cub s o f larger l i tters we i ghed s i g n i f i can tly le s s ( P<O . OOOl ) t h a n c u b s of s maller l i tters . The s e x ra t i o of li tters o f n ewborn cubs a n d ye arl i n g s wa s 45 : 5 5 ( 18 male s, 22 female s ) a nd 5 0 : 5 0 ( 6 male s , 6 female s ) , re s pe c t i v ely. We i g h t s o f adult female s v ar i ed by s e a s o n a nd by re product i v e s t a t u s . Lac t a t i ng female s dro p ped from a n a v erage we i g h t o f 77.4 kg i n w i n ter de n s to 49.1 kg i n J u n e . Al s o , f emale s w i t h n ewborn c u b s i n w i n ter den s w e i g h ed a n a verage of 3 1 . 0 kg h e a v i er t h a n t h ey d i d a s female s w i th y earl i n g s i n w i n ter de n s .