Are low infidelity rates in feral horses due to infanticide?

A growing number of studies conducted on di- verse taxa have shown that extra-pair/group paternity is higher than what would be predicted from behavioral obser- vations alone. While it may be beneficial for females to mate with multiple males, this often results in offspring not sired by the behavioral father, which could influence offspring survival, especially in social mammals. Feral horses (Equus caballus) maintain stable social relationships over several years, usually with one stallion defending a harem band of unrelated mares against other males. Sneak copulations by subordinate males have been observed and mares some- times change bands, both of which can result in foals sired by males other than the dominant band stallion. We measured female fidelity in free-ranging feral horses in 23 bands, with 51 foals over four foaling seasons and tested offspring paternity against parental behaviors. We used 12 polymorphic microsatellite loci and the program CERVUS 2.0 to determine and exclude potential sires. The majority of mares remained in the band with the sire of their foal resulting in most foals being sired by the band stallion. Most foals that were not sired by the band stallion were born in the year after a round-up and we could not determine if they were the result of band chang- ing or sneak copulations. Foals born into a band without their sire had lower survival rates and mothers were significantly more protective of foals not sired by the band s t a l l i on. The s e f i ndi ngs s ugge s t t ha t b a nd s t a bi l i t y increases the reproductive success of mares and support the importance of infanticide risk in equid social structure.