Reproduction and Behavior in Captive Idaho and Columbia Basin Pygmy Rabbits Becky Elias, Rod Sayler, Lisa Shipley Washington State University

Oregon Zoo Northwest Trek Animal Park Washington Department of Fish & Wildlife

Distribution of Pygmy 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 Behavior

Reproductive Success of Females  ID significantly higher than CB on all categories

Reproductive Success of Males  ID significantly higher than CB on all except siring litters (small sample size?)

Reproductive Success  ID and Cross significantly higher than CB

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 Lactation

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

 Emerge 15 days after birth  Female doesn’t cover burrow  Sporadic nursing for several weeks  CB: 3.7 kits Cross: 4.1 kits ID: 3.5 kits  2 – 6 kits/ litter  Max litters/year:  3 in small pens, 4 in our large pen

Breeding Season –CB: March 5 th and May 8 th –ID: *March 1 st and May 25 th –Cross: February 21 st and May 23 rd Earliest & Latest successful copulation

Kit Mortality

Adult Mortality

Kit Weights

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?