Translocations: keep it in the family

31 10 2013
CB_Translocations_Photo
Prairie dogs (Cynomys spp.) comprise 5 species native to North American grasslands. Rather than a ‘dog’ (‘perrito’ or ‘little dog’ in Spanish), this animal is a squirrel (Sciuridae) adapted to ground life. In particular, black-tailed prairie dogs (C. ludovicianus) inhabit the plains between the Frenchman River in Canada and the Mexican stretches of the Sonoran and Chihuahuan deserts. Individuals have a maximum length of 40 cm and weigh up to 2 kg. The global population is currently estimated at some 18 million individuals over an area that has waned by 90% relative to historical ranges. The species is IUCN ‘Least Concern’ and shows a global ‘decreasing’ trend as a result of ongoing habitat loss and fragmentation due to urban development and farming, and susceptibility to Yersinia pestis – a bacteria that causes plague in prairie dogs and other mammals including humans.Colonies, known as ‘coteries’ (from French), are made of several family clans that live in contiguous territories. Clans include one or two males, and several females and juveniles [7]. Females show strong philopatry, while males are the ones that colonise new territories, or mingle with existing clans. Such dispersion pattern, along with daughters deliberately avoiding incest, minimises inbreeding [8]. Burrows consist of >10-m tunnels in which temperatures remain between 5 and 25 ºC irrespective of above-ground temperatures. Prairie dogs are genuine landscape architects with their network of burrows largely increasing edaphic, botanic and zoological diversity [9]. The pic shows two black prairie dogs in Wind Cave National Park (South Dakota, USA) (courtesy of Lisa Savage).

If you have lived in different suburbs, cities or even countries, you will be well aware that changing residence feels very different whether you do it on your own or with someone else. In the latter case, you might have to share tasks, and key decisions have to be made on the basis of everybody’s needs. The situation is analogous when managers decide to move a group of animals or plants from one place to another – so-called translocation.

Translocations involve human-assisted movements of organisms into an area (i) that holds an existing population of the same species (re-stocking), or (ii) where the species has been extirpated (re-introduction) or (iii) is outside its historical distribution (introduction) [1] – this terminology follows 1993 IUCN’s Criteria [1, 3], but is unstable, e.g., see [2]. The rationale behind translocations has obvious merits (e.g., to promote population growth following overharvesting, attenuate human-predator conflicts, rescue endangered species) [2]. However, translocations are complex and have a long record of failed attempts in the history of conservation biology, so the resulting waste of resources has prompted a recent re-appraisal of methods [1-3].

Debra Shier investigated the nuisances of a translocation of a social species such as the black-tailed prairie dog (Cynomys ludovicianus) [4]. Shier tagged, sexed and determined (via capture-recapture and field observations) membership to identified family clans in 973 individuals from Vermejo Park (New Mexico, USA). She then introduced clans to ten dog-free sites with soil quality and vegetation cover akin to the historical distribution of the species. In five of those sites, Shier translocated family clans (4 to 7 individuals per clan) and in the other five sites she freed clans made up of members being picked up randomly (1 male, 2 females, 2 juveniles). During a period of 9-10 months after translocation, Shier monitored the behaviour of females and ultimately re-captured all introduced individuals. She found that 50% of the dogs had survived translocation, and assumed that the remainder had died since individuals rarely disperse more than three km from their natal area, and aerial surveys spotted no dogs in a four-km perimeter around the point of release.

Critically, survival rates increased 3 and 5 times in adults and yearlings (respectively) from non-family to family translocations. Clans from family translocations also produced 137 litters and non-family ones only 38, while the proportion of females with litters was eight times higher in family translocations. Lastly, dogs from family translocations spent less time being vigilant than those from non-family translocations.

 CB_Translocation_Figure
Average demographic rates and frequency of different behaviours (25-hour observations per clan) in black tailed prairie dogs (Cynomys ludovicianus) by the first year after translocating individuals in 2 treatments: clans with and without known family bonds (4). Survival, fertility, as well as feeding and burrowing time, were higher in family than in non-family translocations. The translocation took place over 6 months (in 2001 and 2002) in 4 phases: (i) tagging and diagnosis of consanguinity of ~ 1000 individuals from 5 established colonies; (ii) semi-captivity whereby individuals were allocated to clans of 4 to 7 individuals; (iii) clan acclimation in fenced precincts within each of the sites selected for translocation (5 sites per treatment); and (iv) release.

The study illustrates that the success of the translocation of a social mammal can be enhanced if individuals are moved around in family clans (4). Social cohesion (and clan size) [5] seems to optimise vigilance in response to potential predators, so individuals can spare extra time on vital activities like feeding, socialisation or expansion of the burrow network – the latter activities also bring about the bonus of  improving the body condition and overall fitness of individuals. In contrast, the loss of contact with relatives seems to be particularly detrimental to the survival and fertility of (particularly young) dogs, likely indicating that social learning is somehow impaired when individuals are removed from their family clans. In a species featuring a long history of failed translocations [6], the additional efforts put in studying the social structure of clans prior to translocations can be offset by an increase in translocation success.

Salvador Herrando-Pérez

References

[1] Armstrong, D.P. and Seddon, P.J. (2008). Directions in reintroduction biology. Trends in Ecology and Evolution, 23: 20-25.

[2] Fischer, J. and Lindenmayer, D.B. (2000). An assessment of the published results of animal relocations. Biological Conservation, 96: 1-11.

[3] Pérez, I. et al. (2012). What is wrong with current translocations? A review and a decision-making proposal. Frontiers in Ecology and the Environment, 10: 494-501.

[4] Shier, D.M. (2006). Effect of family support on the success of translocated black-tailed prairie dogs. Conservation Biology, 20: 1.780-1.790.

[5] Hoogland, J.L. (1995). The Black-tailed Prairie Dog: Social Life of a Burrowing Mammal. University of Chicago Press. Chicago.

[6] Truett, J.C. et al. (2001). Translocating prairie dogs: a review. Wildlife Society Bulletin, 29: 863-872.

[7] Foltz, D.W. and Hoogland, J.L. (1981). Analysis of the mating system in the black-tailed prairie dog (Cynomys ludovicianus) by likelihood of paternity. Journal of Mammalogy, 62: 706-712.

[8] Dobson, F. S. et al. (1997). Do black-tailed prairie dogs minimize inbreeding? Evolution, 51: 970-978.

[9] Ceballos, G. et al. (1999). Influence of prairie dogs (Cynomys ludovicianus) on habitat heterogeneity and mammalian diversity in Mexico. Journal of Arid Environments, 41: 161-172.


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