Inter-birth interval in zebras is longer following the birth of male foals than after female foals

Abstract

Mammalian reproductive rates vary among individuals for physiological and environmental reasons. This study aims to determine reproductive rates from an individually monitored population of wild Plains zebras Equus quagga, and to assess the sources of variability in inter-birth intervals. The animals were monitored, where possible, every six months from 2004 to 2011. Thirty nine intervals corresponding to 65 births in 26 mares were identified, using direct observations and faecal steroid monitoring. Mean foaling rate of the population is 0.74 foal/year, and comparable with the literature. There was no significant effect of mother's 2 age, nor of the season of previous birth on the length of inter-birth intervals. Inter-birth interval was significantly longer when the first foal was a male. This finding indicates that additional costs of having a son may delay future reproduction and thus reduce the total number of offspring a mare can have during her lifetime. Individually-based data provide critical information on the determinants of reproductive rates, and are therefore a key to understanding the causes of variations in life-history traits.

Seasonal Patterns of Hormones, Macroparasites, and Microparasites in Wild African Ungulates: The Interplay among Stress, Reproduction, and Disease

“…Though technically nonseasonal breeders [ 23 ], both zebra and springbok in ENP have been observed to breed on a largely seasonal basis, with birth peaks in the wet season [ 11 , 13 ]. Estrogen in pregnant zebras peaks in mid-gestation before declining sharply in the last trimester [ 21 , 51 ]. Estrogen also reaches a sustained peak in mid-pregnancy in springbok, with progesterone peaking just prior to parturition [ 22 , 76 ].…”

“…While both zebra and springbok are not strictly seasonal breeders, both typically give birth during the wet season; zebra often mate again soon thereafter, while springbok often mate in the cold dry season (July). Thus, most mares and ewes experience mid-gestation during the hot dry season [ 11 , 13 , 21 – 23 ]. Reproductive behaviors such as rutting [ 24 ], and gestation and lactation [ 25 ] are particularly energy demanding, and most last for an extended period, potentially leading to chronic stress [ 26 ].…”

Demography of plains zebras (Equus quagga) under heavy predation

“…The sex ratio at birth was taken as balanced. Age-specific survival was derived from the CMR modeling (this paper) and fecundity was estimated at 0.74 (females C3 years-old, Barnier et al 2012) from long-term monitoring of reproduction in this population. Since the age of reproductive females was generally not known, fecundity was considered to be independent of age.…”

“…Many studies on temperate ungulates have reported prime-age survival over 90 % (Gaillard et al 1993;Loison et al 1999;Coulson et al 2001;Festa-Bianchet et al 2003;Toïgo et al 2007; Table 6). Since only two individuals can be classified as 'old adults' during this study (see Barnier et al 2012 for the identification of senescent individuals), senescence is unlikely to be the cause of the low adult survival observed in this zebra population.…”

“…Finally, we investigated which demographic parameters were the most influential in driving the observed demographic patterns. We first built a demographic model (matrix model, Caswell 2001) using age-specific survival and information on age-specific reproduction (Barnier et al 2012). We then compared the population growth rate obtained from this demographic model with observed trends in the population during the study period.…”