bachelor males. Ideally, translocated mares would already be familiar with one another, if possible originating from the same harem. Kaseda et al. (1995) found that mares that had long-term bonds to harem stallions had higher reproductive success than mares that wandered between bands regularly or that had shorter bonds to stallions. Linklater et al. (1999) also found that single mares that were dispersing between bands had lower fecundity, reproductive success, and body condition; had higher parasite levels; and received more aggression from bachelor males than mares in established harems. Moving established groups of females may buffer some of those adverse effects, but it is possible that translocating bonded females without a harem stallion will lead to dissolution of bonds between mares (Rubenstein, 1994).
A second option and one that might further lessen adverse effects is to move intact harems if the harem members and associated stallions can be reliably identified during gathers. That would immediately add new genetic material to the site, but there would be a longer delay in getting that material into the gene pool because foals born into the harem would have to grow up, disperse, and interbreed with members of the resident population.
A third option would be to move bachelor males. This option carries the most risk with respect to getting new genes into the resident population. Stallions that have harems may be quite successful in spreading their genes rapidly via breeding with multiple mares, but obtaining a harem is not easy, and bachelor males may not survive to realize breeding opportunities.
Immediate and long-term infusion of new genetic material may be most likely if intact harems or groups of young mares (immediate) are translocated with a number of males (long term).
Burros are characterized by a less cohesive social structure in which the only long-term relationships are between females and their dependent offspring. Thus, there would be fewer challenges in integrating new females into a burro population, so females would be the first choice for translocation of animals for genetic restoration of burro populations. Males would also be viable candidates for genetic restoration, but introduced males would have to compete with resident males for access to breeding females.
Fertility Control and Implications for Translocation
Introductions of males or females are likely to have different consequences in that adding new females will increase numbers exponentially over time. If population regulation involves female contraception, adding new fertile females could be counterproductive, so adding novel males may be the best way to increase genetic diversity without increasing population size. However, to ensure that the new males become breeders, either a large number would need to be translocated or some of the resident males would need to have their fertility reduced. Alternatively, if curtailing male fertility is the preferred means of population regulation, either a smaller number of novel males can be added to replace a disproportionate number of resident males that are made sterile, or novel females can be added inasmuch as whenever one of the few remaining resident males breeds, he will sire offspring that have genes from the novel females.
Which type of translocation is best to use will depend on a variety of factors, many of which can be tested with a modeling approach in the planning phase (see Chapter 6). Population size, fertility-control methods, and the effects of translocation on Ne will need to be considered. Although translocating males may require fewer total introductions when population size is being regulated because male additions increase the population growth arithmetically rather than exponentially, novel males may find it difficult to obtain harems