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The feral pig (Sus scrofa) is an abundant introduced species with pernicious effects on native species and ecosystems. Its potential reproductive rate is the highest of any ungulate, but data on reproductive rates of feral pigs are limited. We studied reproduction of feral pigs in two regions of southern Texas: the Gulf Coast Prairies and the western South Texas Plains. Pregnancy rates of adults (>21 months) ranged from 78% during winter (December-- February) in the Gulf Coast Prairie to 6% in summer (June-August) in the western study area. Fetal litter sizes in adults tended to be greater (P = 0.11) than those of yearlings. Fecundity ranged from 1.1 female young/year for juvenile females to 4.5 female young/ year in adult females. Sex ratio of fetuses (n = 298) was male-biased (P < 0.05) when data from both study areas were combined. Two seasonal peaks of births were observed (January-March and June-July). Fecundity of pigs in southern Texas was more than four times higher than native ungulates, raising serious questions about dynamics of the ungulate community in this region.
Key words: Sus scrofa, feral pigs, reproduction, breeding, fecundity, Gulf Coast Prairies, South Texas Plains
Suidae has the highest reproductive rate of any ungulate family (Read and Harvey, 1989). Allometrically, suids have large litter sizes, short gestation periods, and early sexual maturity for their body mass (Eisenberg, 1981; Read and Harvey, 1989). These characteristics have been magnified by animal scientists into breeds of domestic pigs (S. s. domesticus) that produce litters of >12 young (Asdell, 1964). Feral pigs are free-ranging swine of varied domestic origin that retain these r-selected traits. For example, average litter sizes of feral pigs in several states range from 4.8 to 7.5 for adults (Baber and Coblentz, 1987; Barrett, 1978; Belden and Frankenberger, 1990; Sweeney et al., 1979). These values compare with litter sizes of 4.5-6.3 for Eurasian wild boar (Ahmad et al., 1995; Mauget, 1991), which represent the original genetic stock for domestic swine. In Texas, Springer (1977) reported that the main season of birth in the Gulf Coast Prairie Ecoregion was January-May (17 of 19 observed pregnancies). Average litter size was 4.2, with two instances of two litters in 1 year being reported. This population had a history of...