Head

REPRODUCTIVE BIOLOGY IN AMERICAN BLACK BEARS

Colleen Olfenbuttel1, and Dr. Michael Vaughan2 Abstract: The Center for Ursid Research in Blacksburg, Virginia is one of only 2 facilities in the United States that temporarily hold wild adult black bears in captivity for research purposes. Few studies have examined fetal development, cub survivorship, and cub growth in black bears due to difficulty in obtaining the necessary data. Most studies that have attempted to document fetal growth have been limited to post-mortem examination of reproductive tracts and fetuses, while published research on post-natal development is virtually non-existent. This study will examine features of female reproductive biology that, until now, are not well documented. An innovative approach we are taking at the Center is the use of transcutaneous ultrasonography to detect for presence of an amnionic vesicle and to measure fetal growth and heart rate. Besides establishing pregnancy status and predicting birth date, there is potential for learning more about pregnancy-associated abnormalities, embryonic and fetal death, and the effects of body condition on adjustments in reproductive effort and cub development. Because we are able to closely monitor cub development, we have also studied the factors that contribute to post-natal cub growth and the consequences of introducing orphaned cubs on growth and survival of natural litters. The results of this research will aid biologists in more accurately assessing female fertility and cub survivorship. This will substantially improve our understanding of the life history and population dynamics of black bears, thus improving decisions regarding management of both recovered and threatened populations.

1Department of Fisheries and Wildlife, Virginia Polytechnic Institute and State University, 149 Cheatham Hall, Blacksburg, VA 24061, USA.2USGS-BRD, Virginia Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Virginia Polytechnic Institute and State University, 148 Cheatham Hall, Blacksburg, VA 24061, USA.

Head

Rump

Parameter Mean Range

Age (years) 7 2-19

Fall weight change (%) 25.7 -12 – 60

Winter weight loss (%) 28 20 – 38

Weight at parturition (kg) 86.9 65.5 – 115.5

Litter size 2.37 1-3

Litter sex ratio 1:1

Fetal detection date Jan. 4 Dec. 20 – Jan. 20

Birth after detection (days) 32.1 4 – 47

Normal

2000g/day

Early

2000g/day

Low

1000g/day

Fall wt. Change % 27.0 19.2 -2.3

Mean cubs detected 2.44 2.2 2.2

Mean age at death 6d 5d 1.5d

No mortality % 52.6 45.5 16.7

Partial loss. % 5.3 9.1 16.7

Complete loss % 42.1 45.5 66.7

Parameter N

Cubs detected in-utero 130

Resorbed 7

In-Utero (unknown) 11

Aborted 2

Total pre-natal mortality

20 (15.4%)

From 1987 - 2002 the Center has held 81 females bears. During that same time, 111 cubs have been born and 47 cubs have been fostered to mothers held at the center.

Cub Weight by Sex

0.0500.0

1,000.01,500.02,000.02,500.03,000.03,500.04,000.0

0-10 11-20

21-30

31-40

41-50

51-60

61-70

71-80

81-90

91-100

Age (days)

We

igh

t (g

)

male female

Cub Weight by Litter Size

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

3500.0

4000.0

0-10 11-20

21-30

31-40

41-50

51-60

61-70

71-80

81-90

91-100

Age (days)

Weig

ht

(g)

1 cub

2 cub

3 cub

Pre-natal detection and growth Post-natal development

Researchers perform ultrasound every 10 days from 10 December until the cubs are born to detect and monitor fetal development.

Visual output from performing an ultrasound. On the right side is the fetus. On the left the cub’s heart rate is recorded. This ultrasound was performed approximately 1 month before parturition.

A picture of a black bear fetus in-utero. The arrows indicate the head and the rump of the cub. Measurements of the cub are recorded using ultrasound.

Ultrasound can detect the occurrence of pre-natal mortality. In this photo, the fetus is being resorbed into the mother’s uterine wall.

Post-natal mortality is detected by the presence of the cubs’ claws in the mother’s feces.

Table 1. The occurrence of pre-natal mortality from 1987 - 2002.

Table 2. Summary of adult female parameters from 1987 - 2001.

Table 3. Results of 3 different diet regimes on adult female fall weight change and cub mortality from 1987 - 2000..

After the cubs are born morphological measurements, such as neck girth and weight, are recorded every 10 days.

Graph 1. Changes in cub weight over time by litter size.

Graph 2. Changes in cub weight over time by sex.

Graph 3. Changes in cub weight over time by the mother’s fall weight change.

Cub weight by mother's fall weight change

0

500

1000

1500

2000

2500

3000

3500

0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90

Age (days)

Wei

gh

t (g

) < 0%

1-20%

21-40%

> 41%