Temporal and Spatial Influences on Fawn Summer Survival in Pronghorn Populations: Management Implications from Noninvasive Monitoring

Monitoring vital rates allows managers to estimate trends in growth rates of ungulate populations. However, connecting the influence of nutrition on ungulate demography is challenging. Noninvasive sampling offers a low-cost, low-effort alternative for measuring nutritional indices, allowing for an increased understanding of the mechanistic relationships between environmental factors, nutrition, and specific population vital rates. We examined the temporal influence of intrinsic and extrinsic factors on pronghorn (Antilocapra americana) fawn recruitment. We collected fresh fecal samples from adult female pronghorn in five subpopulations spanning three sampling periods associated with critical maternal life-history stages (late gestation, early lactation, breeding season) for 2 years to investigate both intra- and interannual influences. Intrinsic factors were fecal glucocorticoid metabolites (FGMs), nutritional indices (fecal nitrogen (FN) and 2,6-diaminopimelic acid (DAPA)), and dietary composition (protein intake of forbs, graminoids, legumes, other, shrubs), while the extrinsic factor was vegetative greenness (normalized difference vegetation index (NDVI)). We found variations in DAPA, protein intake of forbs, variation in forb protein intake, and protein intake of legumes during late gestation positively influenced fawn recruitment. Fecal nitrogen during early lactation showed the strongest positive influence on the recruitment of any measured parameter. Finally, breeding season NDVI and the variation in DAPA values positively influenced the subsequent year's fawn recruitment. Our longitudinal study enabled us to investigate which parameter was most important to specific periods of fawn development and recruitment. We combined the results across five subpopulations, but interpretation and subsequent management decisions should be made at the subpopulation level such that pronghorn subpopulations with low recruitment can be positively influenced by increasing nitrogen on the landscape available to adult females during the early lactation period. As the use of noninvasive monitoring methods continues to expand, we believe our methodologies and results can be broadly applied to other ungulate monitoring programs.

Foetal growth, birth size and energetic cost of gestation in southern right whales

Abstract

The cost of reproduction greatly affects a species’ life history strategy. Baleen whales exhibit some of the fastest offspring growth rates in the animal kingdom. We quantified the energetic cost of gestation for southern right whales (Eubalaena australis) by combining whaling catch records of pregnant females with photogrammetry data on southern right whale mothers and calves from two breeding grounds in Argentina and Australia. The relationship between calf birth size and maternal length was determined from repeated measurements of individual females before and after giving birth. Fetal growth was determined from generalized linear models fitted to fetal length data from whaling operations between 1961 and 1967. Fetal length was converted to volume and mass, using the volume‐to‐length relationship of newborn southern right whales calves, and published tissue composition and energy content estimates. Fetal maintenance costs (heat of gestation) and the energy content of the placenta were predicted from published relationships and added to the fetal growth cost to calculate the total cost of gestation. Our findings showed that fetal growth rates and birth size increased linearly with maternal length, with calves being born at ∼35% maternal length. Fetal length increased curvilinearly through gestation, which resulted in an exponential increase in fetal volume and mass. Consequently, the cost of gestation was very low during the first (0.1% of total cost) and second trimester (4.9%), but increased rapidly during the last trimester (95.0%). The heat of gestation incurred the highest cost for pregnant females (73.8%), followed by fetal growth (21.2%) and the placental energy content (5.0%).

Key points

Baleen whales exhibit some of the fastest fetal growth rates in the animal kingdom. Despite this, the energetic cost of gestation is largely unknown, as well as the influence of maternal body size on fetal growth rates and calf birth sizes.

We combined historical whaling records and drone photogrammetry data to determine fetal growth rates and birth sizes in southern right whales (Eubalaena australis), from which we estimated the cost of gestation.

Calf birth size, and consequent fetal growth rates, increased positively with maternal body size.

The cost of gestation was negligible for southern right whale females during the first two trimesters, but increased rapidly during the last trimester.

These results show that late gestation incurs a significant cost for baleen whale females, and needs to be accounted for in bioenergetic models.

Variations, validations, degradations, and noninvasive determination of pregnancy using fecal steroid metabolites in free-ranging pronghorn

Pregnancy status is a key parameter used to assess reproductive performance of a species as it represents a starting point for measuring vital rates. Vital rates allow managers to determine trends in populations such as neonate survival and recruitment; two important factors in ungulate population growth rates. Techniques to determine pregnancy have generally involved capture and restraint of the animal to obtain blood samples for determining serum hormone levels. Non-invasive pregnancy assessment, via feces, eliminates any hazards between handler and animal, as well as removes handling-induced physiological biases. Using noninvasive fecal sampling, we conducted hormone validations, investigated pregnancy rates, and determined hormone degradation rates across five subpopulations of pronghorn (Antilocapra americana) in Idaho. Samples were collected during April-May of 2018 and 2019 from adult pronghorn of known sex and age class. Metabolites of testosterone, cortisol, 17β-estradiol, and progesterone were measured in fecal samples, and concentrations of estradiol and progesterone were examined for pregnancy determination. Average fecal progesterone metabolite (FPM) levels of pregnant females were more than double compared to levels of nonpregnant females. Fecal estrogen metabolite (FEM) levels did not differ during concurrent sampling. The largest difference in FPM levels between pregnant and nonpregnant females began on 28 April. Pregnancy determination sampling showed average FPM levels for all five subpopulations were significantly different than the nonpregnant female validation group. Nonetheless, pregnancy rates for some subpopulations lacked conclusive estimates due to early fecal sampling. Fecal glucocorticoid metabolites (FGM) levels significantly differed between pregnant females and male pronghorn, but did not differ from nonpregnant females. Degradation rates of FPM and FGM differed across days, with values for FPM from Day 1 being significantly different from all subsequent days, and after Day 9 for FGM, demonstrating the requirement of fresh samples to accurately measure hormone concentrations. We concluded that a noninvasive method to diagnosis pregnancy is possible in pronghorn via progesterone metabolites if fresh samples are collected during late gestation.

Suckling behavior in goitered gazelle: do females invest more in twins or singletons?

The mother-offspring social unit is a universal feature in the social life of all mammals and nursing is the most direct and vital component of maternal investment in young. Living in diverse environments, various ungulate species have different strategies for rearing offspring, from bearing a single, relatively large newborn and supplying only limited amounts of milk, to bearing several relatively small newborns with intensive post-partum lactation. In this paper, we consider the rearing strategy of goitered gazelle with a focus on suckling behavior, which, until now, has never been a subject of special investigation. Adult females of this species in their reproductive prime typically bear twins when environmental conditions are favorable, but the proportion of singletons increases when conditions are unfavorable. We expected that in goitered gazelles suckling intensity would be maximal during the first weeks after birth, and then decrease with the growth of the young; we also expected that twins would demand more energy, but receive significantly less maternal investment per young than singletons. We found that, indeed, suckling behavior had similar dynamics as typical of all bovid species, but our expectation for less maternal investment in twins vs. singletons was wrong. In reality, female goitered gazelles suckled twins significantly more intensively and terminated suckling less often compared to singletons. We concluded that in favorable situations females of high quality have the ability to show significantly more maternal investment in each twin, while singletons are typically born to weaker females. This ability of females to produce mostly twins allows goitered gazelles to take advantage of any favorable opportunity to quickly increase their population in an environment with unpredictable and abrupt yearly changes typical of the arid regions of Central Asia.

The 'big spenders' of the steppe: sex-specific maternal allocation and twinning in the saiga antelope

In polygynous mammals, males generally benefit more from extra allocation of maternal resources than females. However, limitations to sex-specific allocation are usually ignored. We propose the 'allocation constraint' hypothesis, whereby maternal resource allocation is more likely to follow life-history predictions in single sex litters than in mixed sex litters, due to limitations in prenatal resource targeting. Consequently, for polygynous species, males in mixed litters are likely to receive suboptimal maternal investment, which may have a negative effect on lifetime reproductive success. We test this hypothesis for the saiga antelope (Saiga tatarica), a highly polygynous species with the highest level of maternal allocation reported among ungulates. At such high reproductive output levels, the limitations on additional investment in males are likely to be particularly acute. However, we demonstrate high levels of sexual dimorphism in both late-stage foetuses and newborn calves, including within the same litter. Male twins with a brother tended to be heavier than those with a sister. This may be due to allocation constraints or differences in maternal quality. We conclude that an explicit focus on potential constraints can enhance the progress in the field of sex-specific maternal allocation in polytocous species.

Sex-Difference in The Ossification Rate of The Appendicular Skeleton in Capra pyrenaica Schinz, 1838, and Its Utility in The Sex Identification of Long Bones

The main goal of our work is to quantify differences in the rate of ossification in post-cranial Iberian ibex skeletons, related to sex. Another objective is to improve criteria for assessing the sex of post-cranial bones by combining the degree of ossification of the distal epiphysis and biometrical data. Forty Capra pyrenaica skeletons were examined in order to determine the degree of ossification by means of an Ossification Index. Our results evidence that sexual differences in the rate of ossification become visible at 6 months of age. On average, females complete their bone development 2 years before males do. Finally, by means of lineal classification functions which take into account both biometrical and anatomical criteria, we can achieve, in average, a 95.5% of correct sex discrimination within a sample consisting of ibex metacarpi and metatarsi from individuals aging from <1 to 12 years. Therefore, we conclude that the rhythm of ossification in the post-cranial skeleton of C. pyrenaica may be used as a criterion for assessing the sex of skeletal remains and could be applicable to other dimorphic ungulates. Nevertheless, the results obtained for specimens belonging to a particular population may have limited application to other populations with different medium sizes and living at particular densities within habitats with variable quality.

Adaptive adjustment of offspring sex ratio and maternal reproductive effort in an iteroparous mammal

Large mammals in seasonal environments have a pattern of high-reproductive synchrony in spring, but how the timing of reproduction affects resource allocation decisions at different stages of the reproductive cycle remains largely unexplored. By manipulating the timing of conception in reindeer (Rangifer tarandus), we tested how the timing of conception affected sex ratio, gestation length and weight development of mother and offspring. Females that conceived at their first ovulation within the rut had a 60.5% probability of producing a male; in contrast, females that conceived a cycle later had a 31.3% probability of producing a male. Late conceiving females had gestation times that were 10 days shorter and the calves were 0.6 kg (9.2%) lighter at birth and 7.4 kg (14.7%) lighter in autumn. Over the year, female weight changes was similar between the groups suggesting reindeer follow a bet-hedging strategy; reducing the quality of this year's offspring to ensure their own future reproduction and survival. Harvesting is often selective leading to skewed sex ratios and age structure, which may influence the timing of reproduction due to females hesitation to mate with young males. Whenever this hesitation is strong enough to increase the frequency of recycling, harvesting is likely to have profound life history consequences.

Timing of reproduction in wild mink: the influence of spawning Pacific salmon

In many species of seasonally breeding mammals, reproduction occurs later at higher latitudes. Records of timing of reproduction in free-ranging American mink (Mustela vison) in North America and Europe suggest a similar trend. Observations on mink in southeast Alaska, however, revealed a deviation from this pattern, suggesting that factors other than latitude and associated day length may affect timing of breeding for this species in this area. I investigated timing of reproduction and body condition of wild, free-ranging mink on Chichagof Island, southeast Alaska, and hypothesized that seasonal food availability, especially abundant carcasses of spawning Pacific salmon (Onchorhynchus sp.), would determine timing of breeding in this population of mink. Blood progesterone levels, body condition, and testicle lengths were recorded for 24 adult mink, livetrapped from mid-March to late July in 1992 and 1993. Results suggest that these free-ranging mink mate during the later part of April to early May, and parturition occurs in late June to early July. Although male mink seemed to respond to photoperiodism in initiating reproduction, timing of reproduction in female mink was shifted so that lactation coincided with the availability of carcasses of Pacific salmon.