Background information and definitions
Captive breeding involves taking wild animals into captivity and establishing and maintaining breeding populations. It tends to be undertaken when wild populations become very small or fragmented or when they are declining rapidly. Captive populations can be maintained while threats in the wild are reduced or removed and can provide an insurance policy against catastrophe in the wild. Captive breeding also potentially provides a method of increasing reproductive output beyond what would be possible in the wild. However, captive breeding can result in problems associated with inbreeding depression, removal of natural selection and adaptation to captive conditions.
The aim is usually to release captive-bred animals back to natural habitats, either to original sites once conditions are suitable, to reintroduce species to sites that were occupied in the past or to introduce species to new sites. Some captive populations may also be used for research to benefit wild populations.
Studies that investigate the effectiveness of releasing captive-bred mammals are discussed elsewhere. Those studies are not included in this section, unless specific details about captive breeding were included.
Supporting evidence from individual studies
A review of a captive breeding programme in 1978-1992 across Europe (Vogt 1995) reported that the number of institutions successfully breeding European otters Lutra lutra, the number of otters born in captivity and that survived tended to increase over 15 years. These results were not tested for statistical significance. The number of institutions keeping otters remained fairly stable (23-32) from 1978 to 1989, whilst the number of captive animals born and surviving tended to increase from 1978-1983 (born: 0-20; survived: 0-18) to 1984-1989 (born: 18-46; survived: 12-38). Authors reported that until 1990, breeding was only successful in about 10 collections, but that in 1991-1992, when the number of institutions participating in the programme increased to 55, the number that successfully bred otters almost doubled. In 1992 the total captive population was 196 individuals, of which 67% was captive born, and 43 out of 50 cubs survived. In 1990, 36 otter keeping institutions (60% of those co-operating with the studbook) and in 1992 fifty five (91% included in the studbook) took part in the European breeding program for self-sustaining captive populations of otters. These institutions provided information about their captive breeding populations from 1978-1992.Study and other actions tested
A study in 2009-2011 in a captive facility in Indiana, USA (Smyser & Swihart 2014) found that wild-caught Allegheny woodrats Neotoma magister bred in captivity. Over 26 months, 33 pairings resulted in copulation which produced 19 litters (58% pregnancy rate). Those litters comprised of 43 pups (26 male, 17 female), of which 40 (24 male, 16 female) survived to weaning at 45 days. Overall, eight of 12 wild‐caught females produced offspring (1-5 litters) and four of six wild‐caught males sired litters (1-8 litters). In 2009 a captive breeding program was established using eight wild-caught individuals collected from the seven populations in Indiana and four caught from populations in Pennsylvania. The breeding population was maintained at 12-13 animals with a female bias (8:4). Seven new wild animals replaced five in 2010-2011. Individuals were housed in wire mesh enclosures (91 x 61 x 46 cm or 76 x 46 x 91 cm) with access to the opposite sex and an external nest box (23 x 23 x 23 or 36 cm). Enclosures were at 20°C with 13 hours of light/24 hrs. Captive‐reared juveniles were released into wild populations in April-July each year.Study and other actions tested
A review of captive-breeding programmes in 1970-2011 across the world (Alroy 2015) found that the majority of 118 captive-bred mammal populations increased in size. The average annual rate of population increase was 0.028, and only 17 populations (14%) declined (five ‘endangered’ or ‘critically endangered’ according to the IUCN Redlist). Authors reported that positive growth rates were maintained for a large majority of the populations in all IUCN categories except those of ‘least concern’. However, average growth rates declined from 1970-1991 (0.054) to 1992–2011 (0.021). Authors reported that there was a slight decrease in average death rate of populations over time and either no change in average birth rate, or lower birth rates after 1989. Population growth rates did not vary with body mass, but were reported to decrease as the ratio of individuals in programs to populations increased (see original paper for details). Counts of births, deaths and end-of-year totals of individuals in captive populations recorded in studbooks (excluding regional studbooks) were published in the International Zoo Yearbook. Those published from 1970 to 2011 were used to calculate rates of population growth for 118 captive-bred populations (81 species and 37 subspecies). Only populations for which the sum of end-of-year totals was at least 250 over the time period were included.Study and other actions tested