Reproductive strategies in female Mountain and Dorcas gazelles (Gazella gazella gazella and Gazella dorcas)

Observations of reproduction in four gazelle populations in the semi–arid and arid habitats of Israel during three years have revealed intra– and interspecific differences. In the eastern Lower Galilee of northern Israel, female Mountain gazelles (Gazella gazella gazella) reproduce during every month of the year, conceive first at six months of age and exercise long parental care. Females of a population 80 km to the north (Upper Galilee) maintain a seasonal reproductive pattern, conceive first at 18 months of age and have a short parental care period. The latter pattern is similar to the Dorcas gazelle (Gazella dorcas) females of the southern Negev Desert. Interspecific similarities in reproduction of these two populations is attributed to the lack of free water during lactation in both environments where females rely on water available in plant tissue only. The importance of the daily accessibility to water during lactation in female gazelles is discussed. It is suggested that the timing of births and the ability of female gazelles to conceive while lactating are not species-specific characteristics but simply a matter of short-term adaptation to changing environmental conditions common understanding today that animal reproductive strategies are a function of prevailing environmental conditions.     

Distribution of post-weaning Antarctic fur seal Arctocephalus gazella pups at South Georgia

Potentially some of the biggest gaps in our knowledge about the ecology of Antarctic fur seals (Arctocephalus gazella) relate to juvenile animals. We investigated the at-sea distribution of five male and five female fur seal pups post-weaning. The study was carried out at Bird Island, South Georgia during two successive winters using satellite-linked platform transmitter terminals (PTTs). Our results are analysed in relation to pup sex and the physical environment and productivity of those 2 years, as well as in the context of our present knowledge of where post-breeding females and males forage. The available physical and biological data during both of the winters of this study suggest that both years were not unusual. We report marked differences between the sexes with male pups foraging significantly further away from land and their birth site than do females. The pups foraged in areas to the East of Bird Island seldom reported as foraging areas for the adult population. Also as winter progressed they showed a more oceanic distribution leaving the continental shelf, possibly to exploit a different prey source that was more readily available in the upper water column.     

Vagrant Antarctic fur seals, Arctocephalus gazella, in southern Chile

The Antarctic fur seal, Arctocephalus gazella, in the eastern South Pacific Ocean, first reported on Hoste Island, Cape Horn in 1973, and then on the Juan Fernandez Archipelago in 1982 and 1983, was recorded again in October and December 2009 on the southern coast of Chile. Three different individuals were seen simultaneously on a single day at Punta Dungenes, Magellan Strait, and a fourth individual was sighted at the northeastern coast of Almirantazgo Sound, Tierra del Fuego. These records represent the first sightings of live Arctocephalus gazella in southern Chile. Although it is difficult to establish both their origin and rationale for dispersion outside of their distribution range, the substantial breeding population recovery in South Georgia and food shortages during the breeding and post-breeding season are suggested as possible explanations.     

Influence ofOnthophagus gazella on hornfly,Haematobia irritans density in irrigated pastures

Haematobia irritans (L.) breeding in flood irrigated pastures of the lower Colorado Desert of southeastern California continues to remain unacceptably high during warm seasons (>1,000 adult flies per bovine head) despite the presence of moderately abundant populations ofOnthophagus gazella F. This study suggests that densities of > 40–70 adult beetles per dung pad and giving pronounced dung shredding activity, caused fly mortality of 38–56 %. The continued high abundance of adult horn flies on cattle suggests that at > 50% mortality, the pasture environment still produces sufficient flies to saturate cattle, although emigration might be reduced. Additional species of scarabs may be necessary to increase fly mortality. However, the dung drying activity of existingO. gazella significantly could interfere with resident staphylinid beetle breeding, which was significantly lower in pastures whereO. gazella reached densities of 40 per dung pad. Scarab beetle activity might also impede the introduction of superior predatory species for biological control.      

Temporal patterns of milk production in Antarctic fur seals (Arctocephalus gazella)

The timing of milk production in Antarctic fur seals was studied at Bird Island, South Georgia. Like all lactating otariid seals (Pinnipedia: Otariidae), Antarctic fur seal females alternate between short nursing periods ashore and regular foraging trips to sea. Females do not necessarily return to the colony with full mammae, which indicates that mammary volume capacity is unlikely to limit foraging trip duration. Upon arrival at the colony, milk fat (r²= 0.33, P < 0.04) and protein (r²= 0.60, P < 0.002) content were positively correlated to the time spent at sea. A similar trend was observed in the milk produced on land. The rate of milk energy production was much lower at sea (5.02 ± 0.05 MJ day^-1) than on land (23.66 ± 4.4 MJ^-1 day^-1). The rate of milk energy production during the foraging trip was negatively correlated to the time spent at sea (r²= 0.29, P < 0.05), whereas the rate of milk energy production on land was positively correlated (r²= 0.61, P < 0.001) to the duration of the preceding foraging trip. The total amount of milk energy delivered to the pup during each twoday nursing period was positively correlated (r²= 0.60, P < 0.002) to the duration of the previous foraging trip. The overall rate of milk energy delivery, however, was independent of foraging trip duration. This accords with previous observations that the growth rates of Antarctic fur seal pups are unaffected by maternal foraging trip duration patterns.     

Fasting metabolism in Antarctic fur seal (Arctocephalus gazella) pups.

The metabolism of 52-73-day old Antarctic fur seal pups from Bird Island, South Georgia, was investigated during fasting periods of normal duration while their mothers were at sea foraging. Body mass decreased exponentially with pups losing 3.5-3.8% of body mass per day. Resting metabolic rate also decreased exponentially from 172-197 ml (O2) x min(-1) at the beginning of the fast and scaled to M(b)(0.74) at 2.3 times the level predicted for adult terrestrial mammals of similar size. While there was no significant sex difference in RMR, female pups had significantly higher (F(1,18)=6.614, P<0.019) mass-specific RMR than male pups throughout the fasting period. Fasting FMR was also significantly (t(15)=2.37, P<0.035) greater in females (823 kJ x kg(-1) x d(-1)) than males (686 kJ x kg(-1) x d(-1)). Average protein turnover during the study period was 19.3 g x d(-1) and contributed to 5.4% of total energy expenditure, indicating the adoption of a protein-sparing strategy with a reliance on primarily lipid catabolism for metabolic energy. This is supported by observed decreases in plasma BUN, U/C, glucose and triglyceride concentrations, and an increase in beta-HBA concentration, indicating that Antarctic fur seals pups adopt this strategy within 2-3 days of fasting. Mean RQ also decreased from 0.77 to 0.72 within 3 days of fasting, further supporting a rapid commencement of protein-sparing. However, RQ gradually increased thereafter to 0.77, suggesting a resumption of protein catabolism which was not substantiated by changes in plasma metabolites. Female pups had higher TBL (%) than males for any given mass, which is consistent with previous findings in this and other fur seal species, and suggests sex differences in metabolic fuel use. The observed changes in plasma metabolites and protein turnover, however, do not support this.     

Population size and age determination in the Antarctic Fur seal Arctocephalus gazella

The population of Antarctic Fur seals Arctocephalus gazella at South Georgia is increasing rapidly and is therefore of great interest. Investigations of the population depend on two main techniques.
(1) Population assessment, because the population size is now too large for direct counts to be completely reliable, and serious underestimates are appearing in areas of high density. Aerial photography was used but needs further refinement before it becomes a consistently useful technique. Marking all pups on sample beaches was largely unsuccessful because pups moved from beach to beach before they could all be marked. A mark–recapture method was finally adopted and indicated that the numbers of pups present may be up to 54% higher than the numbers actually counted.
(2) The process of age determination from tooth characters, which is more difficult for Fur seals than other pinnipeds. The preparation and interpretation of the teeth of breeding cows is described, based on eleven specimens of known age. The most accurate results are obtained from whole teeth up to the age of 6, but thereafter interpretation of cement and dentine layers in thin sections must be used. It is concluded that while young animals are aged quite accurately, there is probably a tendency to underestimate the age of seals of more than 9 years.     

Horn asymmetry and fitness in gemsbok, Oryx g. gazella

The relationship between fluctuating asymmetry in horns of gemsbok(Oryx g. gazella) and a number of fitness components was determinedin a field study in Etosha National Park, Namibia. The lengthand width of horns and skull length demonstrated fluctuatingasymmetry. Both males and females with asymmetric horns werein poorer condition than symmetric individuals. Individualsof both sexes with symmetric horns more often won aggressiveinteractions at waterholes. Although symmetric individuals spentmore time in dense vegetation, their vigilance rate was nothigher than that of asymmetric individuals. Territorial, singlemales had more symmetric horns than males in herds, suggestingthat mating success was inversely related to horn asymmetry.Females with symmetric horns more often had calves than asymmetricfemales. Horn asymmetry thus appears to reliably reveal phenotypicquality as demonstrated by a suite of fitness components.[BehavEcol 7: 247-253 (1996)]     

Growth rates of Antarctic fur seal Arctocephalus gazella pups at South Georgia

Large numbers of pups of the Antarctic fur seal were weighed at regular intervals through their rearing period in six seasons between 1972 and 1981 at South Georgia. Growth rates and birth and weaning weights were estimated from linear regressions of mean weight on mean age. Female pups had significantly lower growth rates and weaning weights than males, but higher variances for all growth parameters. This may reflect the importance to males of polygynous species of attaining high body weight. Except for an inverse relation between growth rate and birth weight there were no systematic relationships between growth parameters. Seasonal differences in growth rates were substantial and there was no indication that the continuing rapid population increase was affecting pup growth rates. The use of these data in detecting seasonal variations in local food availability is discussed. Preliminary estimates of the energy costs of pup rearing indicate that pup existence metabolism consumes c. 80% and mass gain to weaning only c. 15% of the energy provided by the female.     

Fish prey of Antarctic fur seals Arctocephalus gazella at Ile de Croy,Kerguelen

 The composition of Antarctic fur seal prey was assessed through analysis of scats collected in March 1994 on Ile de Croy, Iles Nuageuses. Fish remains predominated in samples, occurring in 95% of droppings. A total of 968 otoliths allowed the identification of 16 fish species. Myctophid fish (12 species) dominated the diet both by number (94% of the otoliths) and by fish reconstituted mass (76%). Three fish species constituted together 87% of the reconstituted mass: the myctophids Gymnoscopelus nicholsi (52%) and G. piabilis (12%), and the channichthyid Champsocephalus gunnari (23%). Prey distribution suggests that during late summer seals forage in upper slope waters in the northeast of the Kerguelen Archipelago. Received:1 March 1996/Accepted: 20 May 1996     

The diet of Antarctic fur sealsArctocephalus gazella during the breeding season at South Georgia

 The diet of lactating female Antarctic fur seals Arctocephalus gazella at South Georgia was investigated during the pup-rearing period (January/March) of 1991–1994. Antarctic krill Euphausia superba was the main prey item, occurring in 88% of all scats (n=497), whereas fish occurred in 47% and squid in 5% of all scats. There was considerable intra- and inter-annual variation in the characteristics of krill taken by fur seals. The distribution of krill sizes taken suggests that fur seals are not actively selecting particular sizes of krill and, therefore, that the krill in the diet reflects the krill available around South Georgia. The absence of group 3 krill (44–48 mm in length) in the South Georgia area, as indicated by their absence in the diet of seals, is suggested as a possible reason for low availability of krill and the subsequent reproductive failure among krill predators. The frequency of occurrence of fish was much higher than in previous studies; the pattern of fish consumption showed a consistent seasonal pattern in 3 of the 4 years studied. Of the total number of the myctophid Protomyctophum choriodon, the most numerous fish taxon, 98% were taken between early February and the middle of March. Champsocephalus gunnari and Lepidonotothen larseni agg., which both feed on krill, dominated the fish component of the diet outside this period and together constituted 94% of the total estimated biomass of fish consumed. The intra- and inter-annual variability in the diet of Antarctic fur seals emphasise the need for diet studies to be conducted during the entire pup-rearing periods of several years. Received: 15 March 1995/Accepted: 13 May 1995     

Conservation implications of midden selection and use in an endangered gazelle (Gazella gazella)

This study examines midden selection and use by mountain gazelles Gazella gazella in central Saudia Arabia and the implications of middens (dung piles) for the conservation of this species. Specifically, we tested poachers' claims that mountain gazelles are easy to kill because midden use was predictable and conspicuous. We found that midden selection in mountain gazelles is non-random, with middens typically located at the base of the most conspicuous and largest trees, although the choice of midden sites is also influenced by tree species. Middens clearly have olfactory importance; the majority of mountain gazelles that visited middens were observed sniffing the ground. Mountain gazelles visit middens at night, which corroborates poachers' claims that the animals are easily hunted at night through spotlighting. Although the use of open habitats that are accessible to automobiles makes gazelles vulnerable to hunting and being run down, our data suggest that midden use is also an attribute that makes gazelles susceptible to hunting. Poachers can locate gazelles because of middens' predictable locations, as they are placed at prominent landmarks, are visually conspicuous as large dung piles, and are visited at night, which allows the animals to be found through spotlighting. Other taxa that use predictable and prominent landmarks, or communicate through visually conspicuous methods could also be susceptible to poaching.     

Territoriality and breeding behaviour of adult male Antarctic Fur seal, Arctocephalus gazella

The social organization and behaviour of 35 individually recognizable territorial male Antarctic Fur seals ( Arctocephalus guzellu ), were studied during the breeding season at South Georgia. Adults of both sexes remain at sea throughout the winter. Among the first bulls ashore were those which had the longest territorial tenures. The mean period of tenure for 13 bulls seen to copulate was 34.3±9.0 days. New bulls continued to arrive and fight for territories on the breeding beach throughout the study period. Many were successful and mean territory size declined from about 60 m² in mid-November to 22 m³ in December. More than 3000 boundary displays between known bulls were recorded and analysed. These were largely ritualized although in 14% of displays bites were exchanged. Outright fighting was infrequent in relation to the total number of inter-male encounters. 94% of of the fights occurred on the first day a pair of bulls became neighbours. Less than 50% of bulls holding territory were seen to copulate and the mean copulation frequency for these bulls was 10. During late December, by which time most females had mated, adult males ceased to maintain their territories actively and many abandoned them completely. Features of the social organization are compared with those of other otariid seals and the interrelationships between period of tenure, territory size, form of boundary display and copulation frequency are discussed in relation to environmental and social influences. Within fur seals and sea lions, differences in social organization during the breeding season do not seem to be related to phylogenetic differences.     

Kin selection may influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)

Fostering confers obvious advantages to the offspring but is seemingly costly to the caregiver. Such behaviour is particularly paradoxical in seals where the energetic investment in milk is very high and has led to the suggestion that this behaviour may have evolved through either kin selection or reciprocity. We used a combination of genetic and behavioural data to investigate whether kin selection plays a role in the fostering behaviour observed in a well-studied population of Antarctic fur seals (Arctocephalus gazella) from Bird Island, South Georgia. Genotypic data from eight highly polymorphic microsatellite markers were used to estimate relatedness among mother-pup pairs, foster mother-pup pairs and the total population. Mean relatedness was found to be significantly higher for foster mother-pup pairs than that observed for the total population, suggesting that kin selection could have a role in the maintenance of fostering behaviour in this species.     

Genetic tagging reveals extreme site fidelity in territorial male Antarctic fur seals Arctocephalus gazella

Genetic tagging, the identification of individuals using their genotypes, provides a powerful tool for studying animals that are difficult to observe or identify using conventional techniques. However, despite being widely adopted by conservation biologists, the full potential of this approach has yet to be realized. Here we used genetic recapture data to quantify male site fidelity at a colony of Antarctic fur seals where an aerial walkway provides unprecedented access and individual positions are determined daily to 1 m accuracy. Because males are too large and aggressive to be captured and fitted with conventional tags, we remotely collected 770 tissue samples over eight consecutive seasons and used nine-locus microsatellite genotypes to reveal 306 genetic recaptures among 464 unique individuals. Within seasons, males are highly site-faithful, with any movements that occur tending to take place before the period when females come into oestrus. Of those males that return to breed over successive seasons, almost half return to within a body length of where they were before. The discovery of such extreme site faithfulness has implications for the population structure and mating system of fur seals and potentially other colonially breeding species.     

Global distribution patterns provide evidence of niche shift by the introduced African dung beetle Digitonthophagus gazella

The establishment of cattle ranches throughout the world has prompted the release of dung beetles as biological control agents that reduce pasture fouling and control dung-breeding flies. One of these beetles, Digitonthophagus gazella (Fabricius) (Coleoptera: Scarabaeidae), that is native to southeast Africa, has been introduced into the Americas, Australia, and New Zealand. Distribution records for this species have been used to develop climate models of potential future establishment. Recent studies, however, identify D. gazella as a complex of seven species. Taking into account this revision, and the clear identification of the records belonging to the actual D. gazella, we developed environmental models to identify factors that have contributed to the establishment of this species across regions and habitats. We compared the environmental conditions of D. gazella in its native range against those in the regions where the species has or has not established. Our results indicate that D. gazella is still absent in certain parts of Central and South America and parts of Africa where it could potentially establish. We speculate that its distribution in Africa is limited by competitive exclusion. The introduction of D. gazella in America is relatively recent, such that the full extent of its distribution has probably yet to be realized. In Australia and North America, D. gazella is present in regions not predicted according to its native environmental conditions. This discrepancy may reflect a lack of competitive exclusion, phenotypic plasticity, and/or genetic adaptation. Our analyses suggest that the species has the ability to adapt to a wide range of environmental conditions that are extremely different from those in their native region. The species represents a useful case study to indicate that an introduced species may expand its realized niche beyond what is expected based on apparent environmental limits in the species native range.