Reproduction and Behavior in Captive Idaho and

Columbia Basin Pygmy Rabbits

Becky Elias, Rod Sayler, Lisa Shipley

Washington State University

• Washington State University• Oregon Zoo• Northwest Trek Animal Park• Washington Department of

Fish & Wildlife

Distribution of Pygmy Distribution of Pygmy Rabbits Rabbits

Background

• Smallest rabbit in North America

• Sagebrush foragers• Dig their own

burrow• Columbia Basin

(CB) pygmy rabbits listed as endangered

Background

• Decline of the Columbia Basin pygmy rabbit linked to:– Loss and fragmentation of deep soil

sagebrush-steppe habitat– Predation– Disease– Cattle grazing– Inbreeding depression

Timeline

• 1995 – Recovery plan adopted for Columbia Basin (CB) pygmy rabbits

• 2001 – Population crash results in an emergency action plan and an emergency listing as endangered. Oregon Zoo (OZ) develops captive breeding protocol using Idaho (ID) pygmy rabbits, and remaining CB rabbits are brought into captivity

• 2002 – Captive breeding of CB pygmy rabbits begins at OZ, Washington State University (WSU), and Northwest Trek (NWT)

• 2003 – CB pygmy rabbits achieve federal listing as endangered. Beginning of intercross pairings between CB and ID pygmy rabbits

Outline

• Breeding behavior• Reproductive

success• Nest building • Gestation, birth,

and lactation • Weights & Diet• Mortality & survival• Management

implications

Breeding

• Wilde (1978) and Fisher (1979)• Breed mid-February to mid-May• Induced ovulators• Gestation period of 39 days• Up to three litters a year• Average litter size of 6 kits• No evidence on kits in burrows; hide at

base of sagebrush plants

Diet

• 2001 – 2002: Lab Diet (high fiber) /Bunny Basics (timothy hay mix)

• 2004 (at WSU only): Purina breeder’s diet (high protein)

Breeding Pens

Large breeding pen

Data Collection

• Breeding & Maternal Behaviors – Digital video recorder– Bullet cameras and day/night cameras– Pens open for ~ three days– Recorded chasing, copulation, nest-building, birth, and

lactation

• Reproductive Success– Female counted as pregnant when she built a natal nest– All kits found, no matter what age, used for reproductive

success

Results

Breeding Behavior• Male or female initiated chases

• Lasted seconds to several minutes

• Copulation while chasing or female stopped and allowed male to mount

• Brief copulation

Breeding BehaviorCB ID p-value

Time before breeding chases began 9.5 hrs 1.9 hrs 0.06Time until copulation after breeding began 22 hrs 8.9 hrs 0.07Time male spent chasing before 56.7 min 7 min 0.04Time male spent chasing after 20.2 min 4.1 min 0.02Total time spent chasing 87.4 min 18 min 0.01

Reproductive Success of Females

ID significantly higher than CB on all categories

CB Cross IDBecoming pregnant 52% 65% 100%Pregnancies per female 0.69 0.95 1.63Kits per female 2.1 3.5 4.9

Reproductive Success of Males

ID significantly higher than CB on all except siring litters (small sample size?)

CB Cross IDSiring litters 54% 94% 90%Sirings per male 0.83 1.25 3.2Kits per male 2.5 4.1 9.3

Reproductive Success

ID and Cross significantly higher than CB

22

45

62

0

10

20

30

40

50

60

70

CB Cross ID

% o

f p

airi

ng

s re

sult

ing

in

p

reg

nan

cy

Why is CB reproduction low?

• Problem with males, females, or both?

• Males: problem with copulation?

• Females: physiological - ovulation, behavior – aggression before successful copulation?

• Hybrid studies

Possible Answers• Captivity

– Problems breeding in captivity• Behavior

– Sending/receiving proper behavioral cues• Weights

– Underweight animals do not produce effectively– CB males have produced better since the introduction of

the higher protein diet• Potential Inbreeding Depression

– Decreased mating activity– Longer time before first litter– Increased litter failure– Low sperm count/failed ovulation

Gestation, Birth, and Gestation, Birth, and LactationLactation

Nest Building

• 13 days post-conception

• Dig separate burrow; 16.5 – 35.5 cm

• Use hay to make nest

• Pluck fur from abdomen and line nest shortly before birth

Gestation

• Gestation period– CB: 22.6 days (n=2)

ID: 24.0 days (n=9) p=0.03

– Cause of difference• CB litters born premature• Genetic drift & non-adaptive variation;

adaptive variation; inbreeding depression

Birth• 2 morning, 4 afternoon,

3 night

• Female plucked fur from her abdomen, cleaning, and opening burrow

• At burrow entrance

• 14.8 minutes

• Covers burrow entrance

Kits• Eyes closed

• Little fur

• Gray to black skin

• Pink bellies

• ~15 grams

Lactation• Open once or

twice a day to nurse

• Kits come to the surface to nurse, with female sitting at the burrow entrance

• 10.6 minutes

• Recovers burrow

• Night (6pm-11pm)

• Morning (5am-9am)

Lactation

0

5

10

15

20

25

30

350

10

0

03

00

05

00

07

00

09

00

11

00

13

00

15

00

17

00

19

00

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23

00

Time of Day (hr)

Nu

mb

er

of

Nu

rsin

gs

1 nursing

2 nursings

• No apparent correlation between number of nursings per day and litter size, time of year, or health of litter

Emerge 15 days afterEmerge 15 days after birth birth

Female doesn’t coverFemale doesn’t cover burrow burrow

Sporadic nursing forSporadic nursing for several weeks several weeks

CB: 3.7 kits Cross: 4.1 CB: 3.7 kits Cross: 4.1 kitskits ID: 3.5 kits ID: 3.5 kits

2 – 6 kits/ litter2 – 6 kits/ litter

Max litters/year: Max litters/year:

3 in small pens, 4 in 3 in small pens, 4 in our large pen our large pen

Breeding Season

– CB: March 5th and May 8th

– ID: *March 1st and May 25th

– Cross: February 21st and May 23rd

0

1

2

3

4

5

6

7

8

9

Feb(3) Mar(1) Mar(3) April(1) April(3) May(1) May(3) June(1)

Date by Month (week)

# s

uc

ce

ss

ful c

op

ula

tio

ns

CB

other

Earliest & Latest successful copulation

Kit Mortality

coccidiosis24%

myodegeneration10%

maternal neglect11%

unknow n30%

acute diarrhea/enteritis

6%

clostridiosis4%

other11%

trauma4%

Adult Mortality

acute

diarrhea/enteritis14%

mycobacteriosis61%

other16%

trauma9%

Kit Weightsy = 165.75x0.3185

R2 = 0.9327

y = 143.67x0.3301

R2 = 0.9324

050

100150200250300350400450500

4 6 8 10 12 14 16 18 20 22 24 26

Age (weeks)

Wei

gh

t (g

ram

s)

Adult Weights

• CB males and females same weight as ID before breeding season

• CB males (-32g) and females (-24g) lost weight.ID males (+11g) and females (+27g) gained weight

• New data: both males and females fed the higher protein diet, gained weight (19g for males, and 17g for females)

Large pen weights

• At 26 weeks (near adult weight), animals in the large pen weigh much more than animals in the small pens

• Males– Large pen: 523g– Small pen: 424g

• Females – Large pen: 590g– Small pen: 431g

Captive Population Growth: first 3 years

• Growth rate of the CB population was 1.2 during the first 3 years of the study

• Projected population: 60 CB rabbits in 5 years of captive breeding

• 10.4% chance of population increasing to 100 and 0.1% chance of crashing to 5

Adult Survival

• 2001: 88%• 2002: 56%• 2003: 63%2004: 43%• All years: 63%

Kit Survival

• 2001: 80%• 2002: 47%• 2003: 59%2004: 23%• All years: 52%

Conclusions

Inbreeding•Low reproductive performance•Health problems

Diet•Animals weigh more on a high protein diet•Possibly better reproduction

Population growth•Mediocre at best – long-term viability questionable•Success in any given year is unpredictable

Management Implications

NO Columbia Basin rabbits have been found in the wild since 2001 – may be extinct

– Must control disease– Explore reproductive limitations and potential– Increase genetic diversity– Intercross rabbits to maintain unique CB

alleles

QUESTIONS?