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Reproduction and Behavior in Captive Idaho and Columbia Basin Pygmy Rabbits : 

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 Rabbits : 

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: 

Breeding Pens

Large breeding pen: 

Large breeding pen

Data Collection : 

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



Breeding Behavior: 

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: 

Breeding Behavior

Reproductive Success of Females: 

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

Reproductive Success of Males: 

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

Reproductive Success: 

Reproductive Success ID and Cross significantly higher than CB

Why is CB reproduction low?: 

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: 

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: 

Gestation, Birth, and Lactation

Nest Building: 

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: 

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

Kit Mortality: 

Kit Mortality

Adult Mortality: 

Adult Mortality

Kit Weights: 

Kit Weights

Adult 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: 

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: 

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: 

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

Kit Survival: 

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: 

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



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