Bycatch in longline fisheries is a major contributor to the global decline of albatrosses. Sexual segregation at sea often leads to unequal overlap with different fisheries, resulting in sex-biased bycatch, exacerbating the impact on a population level. In great albatrosses (Diomedea spp.), males (the larger sex) tend to spend more time at higher latitudes than females, attributed to competitive exclusion or differences in flight performance mediated by the pronounced sexual size dimorphism (SSD). Consequently, larger numbers of females are bycaught in pelagic longline fisheries in subtropical and temperate areas. Although this has been shown for Diomedea exulans, it has not been confirmed for all great albatross species. Here we examined the degree of SSD and developed discriminant functions to determine species and sex in D. epomophora and D. sanfordi; species that are often killed in several fisheries in the Southern Hemisphere. Based on a large sample of albatrosses bycaught off Uruguay, both species showed substantial SSD. Discriminant functions assigned species and sex to otherwise indeterminate individuals with 90–100% accuracy. Based on all birds identified (n=128), bycatch in the pelagic longline fishery was female-biased, indicating sexual segregation at sea. The discriminant functions presented enable species and sex to be identified, providing critical data for future bycatch assessments.

The reproductive biology of the pelagic thresher shark Alopias pelagicus, was analysed based on 241 individuals (101 males and 140 females). Samples were collected from April 2005 to February 2006, from the artisanal fishery in Manta, Ecuador. Males ranged from 68 to 183 cm precaudal length (PL); females ranged from 70 to 180 cm PL. In embryos, sexual proportion was 1F:1M; while in adults the proportion was 1.4F:1M, which suggests sexual segregation in maturing individuals. We showed differences in the development of reproductive structures according to the reproductive condition, and in males the size at maturity occurs at 144.3 cm PL and in females at 151.4 cm PL. We recorded 33 pregnant females that presented one embryo in each uterus in different developmental stages. The results of this study provide information on reproduction of the species that will help to establish an appropriate fisheries management.

This study examined the foraging behaviour of a resident bird species, the rufous-capped warbler (RCWA, Basileuterus rufifrons), in a shaded-coffee farm in Chiapas, Mexico. Unlike many resident species that use shaded-coffee agroecosystems seasonally, RCWAs do not move to other habitats when migrants are present. RCWA foraging was compared when migrant birds were present (dry season) and absent (wet season). It was hypothesized that RCWAs would exhibit a seasonal foraging niche shift because of resource competition with migrants. Observations from both the canopy and coffee understorey show that RCWAs foraged almost equally in both vegetative layers during the wet season although they were more successful foraging in the canopy. In the dry season, migrants foraged primarily in the canopy and RCWAs shifted so that 80% of RCWA foraging manoeuvres were in the understorey. At that time RCWAs foraged less successfully in both vegetative layers. Avian predation in the dry season was found to reduce densities of arthropods by 47–79% in the canopy, as opposed to 4–5% in the understorey. In the canopy, availability of large (>5 mm in length) arthropods decreased by 58% from the wet to dry season. Such resource reductions could have caused the RCWA foraging niche shift yet other alternative or additional hypotheses are discussed. Shifts in foraging niche may be a widespread mechanism for some small insectivorous residents to avoid seasonal competition with abundant migrant species.

We examined whether synchrony and timing of breeding influenced magnitude and timing of sexual segregation in sympatric western grey kangaroos Macropus fuliginosus and red kangaroos M. rufus, at Hattah-Kulkyne National Park, in south-eastern Australia. These species vary in the synchrony and timing of their mating activity: western grey kangaroos mate during a relatively synchronous period, predominantly during spring, while red kangaroos mate throughout the year. Surveys were conducted during autumn and spring 2000 to examine seasonal patterns of mating activity, group composition, spatial distribution, and habitat selection of adults of both species. Habitat selection was also examined by analysing data from culls conducted from 1998 to 2002. Mating activity occurred synchronously in western grey kangaroos, thus, like in many ungulate species, there was a time of peak segregation, during autumn, when females were in lactational anoestrus, and a time of peak aggregation, during the period of peak mating activity in spring. In red kangaroos, mating activity occurred during both seasons, but showed a slight peak during autumn. Consequently, segregation was weaker than in western grey kangaroos but occurred through-out the year, with a slight peak during spring. The degree of social and spatial segregation in western grey and red kangaroos was comparable to that in ungulates, while habitat segregation was considerably lower than is typically seen in ungulates. These results indicate that breeding phenology is a major factor involved in sexual segregation, and highlight the importance of directing attention at the general conditions underlying this phenomenon.

Patterns of association in many ungulate species vary throughout the year, with males periodically segregating from females. Sexual segregation can occur if males and females use different habitats (habitat segregation), occupy exclusive ranges (spatial segregation) or occur in separate social groups (social segregation). Previous studies on social segregation in ungulates have focused mostly on non-reproductive periods and species in temperate systems with short mating seasons. This study examined social segregation in African buffalo Syncerus caffer at Hluhluwe-iMfolozi Park, South Africa, during their 6-month mating season. During this period, mature male buffalo alternated between joining mixed-sex herds which comprise females and young, and small all-male groups. Activity patterns of male buffalo in both group types were examined to determine if differences in time allocation or activity asynchrony could explain the observed segregation. Mature males foraged for less time than both adult females and younger males when they were with mixed herds. Mature male buffalo differed in how their active time was apportioned to foraging and reproductive activities between the two group types. Females maintained group cohesion despite only low synchrony in activity, therefore segregation of male buffalo could not be explained by the activity budget hypothesis. For males in mixed-sex herds, reproductive activities were apparently at the expense of foraging time. The high time and energy costs of reproductive activities were probably responsible for the periodic separation of male buffalo from mixed herds during the extended mating period.

In constructing large vegetated mounds, Macrotermes termites play a key functional role in many African savanna systems. This study focuses on ungulate feeding on Macrotermes termitaria vegetation in Lake Mburo National Park, Uganda. With the exception of oribi Ourebia ourebi, all the species studied (i.e. impala Aepyceros melampus, Burchell's zebra Equus burchelli, Defassa waterbuck Kobus ellipsiprymnus, topi Damaliscus lunatus, bushbuck Tragelaphus scriptus and warthog Phacochoerus africanus) grazed preferentially on mound areas compared to the adjacent savanna. Ruminant species grazed closer to termitaria than non-ruminants and female impala both browsed and grazed closer to mounds than males. No sexual difference in grazing distance to mounds was found for waterbuck.

In most social ungulate species, males are larger than females and the sexes live in separate groups outside the breeding season. It is important for our understanding of the evolution of sociality to find out why sexual segregation is so widespread not only in ungulates but also in other mammals. Sexual body size dimorphism was proposed as a central factor in the evolution of sexual segregation in ungulates. We tested three hypotheses put forward to explain sexual segregation: the predation-risk, the forage-selection, and the activity budget hypothesis. We included in our analyses ungulate species ranging from non-dimorphic to extremely dimorphic in body size. We observed oryx, zebra, bighorn sheep and ibex in the field and relied on literature data for 31 additional species. The predation-risk hypothesis predicts that females will use relatively predator-safe habitats, while males are predicted to use habitats with higher predation risk but better food quality. Out of 24 studies on different species of ungulates, females and their offspring chose poorer quality but safer habitat in only eight cases. The forage-selection hypothesis predicts that females would select habitat based on food quality, while males should prefer high forage biomass. In fact, females selected higher quality food in only six out of 18 studies where males and females segregated, in eight studies there was no difference in forage quality and in four studies males were in better quality habitat. The activity budget hypothesis predicts that with increasing dimorphism in body size males and females will increasingly differ in the time spent in different activities. Differences in activity budgets would make it difficult for males and females to stay in mixed-sex groups due to increased costs of synchrony to maintain group cohesion. The predictions of the activity budget hypothesis were confirmed in most cases (22 out of 23 studies). The heavier males were compared to females, the more time females spent foraging compared to males. The bigger the dimorphism in body mass, the more males spent time walking compared to females. Lactating females spent more time foraging than did non-lactating females or males. Whether species were mainly bulk or intermediate feeders did not affect sexual differences in time spent foraging. We conclude that sexual differences in activity budgets are most likely driving sexual segregation and that sexual differences in predation risk or forage selection are additive factors.

Inter-sexual segregation between habitats or between sites within a habitat is very widespread in sexually dimorphic ungulates. As an explanation, it has been suggested that males, because of their larger forage requirements, are driven from preferred, high quality forage habitats into marginal habitats of lower forage quality but higher forage biomass by female competition (‘indirect competition hypothesis’). However, this hypothesis has hardly been tested. In the present study, we tested the indirect competition hypothesis for site segregation of red deer on the Isle of Rum, Scotland, within two vegetation communities: short Agrostis/Festuca grassland and Calluna heath. We predicted that: (1) males should choose sites within each vegetation community that are of higher forage biomass but lower forage quality, than sites selected by females; (2) the degree of inter-sexual site segregation should be highest within the vegetation community in which indirect competition was most intense. We found that the sexes were significantly segregated between sites within both vegetation communities, but males did not use sites of lower forage quality or of higher forage biomass than did females. Moreover, degree of site segregation was not significantly higher in the vegetation community in which competition was more intense (i.e. short Agrostis/Festuca grassland). We conclude that the indirect competition hypothesis cannot explain site segregation in red deer on the Isle of Rum.

Numerous field studies have attempted to assess competition between ungulates through the analysis of resource overlap. However, interpreting the results of these studies has been problematic because low overlap may be the outcome of historical competition and high overlap will result in competition only when that resource becomes limiting. In New Zealand, increasing densities of introduced Himalayan tahr Hemitragus jemlahicus have competitively excluded introduced Alpine chamois Rupicapra rupicapra, but where densities of tahr have been reduced the two species can coexist. This study evaluated the role of habitat selection in the coexistence of these two recently sympatric ungulates in Carneys Creek, eastern Southern Alps, New Zealand. Seasonal habitat selection was estimated by observing unmarked male tahr, female tahr and chamois monthly for 25 months. The proportional availability of six habitats (grassland, grass bluff, rock bluff, shrubland, scree and snow) was measured from aerial photographs taken in each of the four seasons. Although the null hypothesis that tahr and chamois select habitats similarly was rejected in three of four seasons, there was high overlap in preference for grassland and shrubland, and avoidance of scree and snow. Tahr were more often observed in grass bluff and rock bluff than were chamois. Overlap in habitat selection was greatest during winter when snow dominated the landscape, reducing the availability of vegetated habitats. Using Hurlbert's statistic, the niche breadth of chamois was significantly smaller than that of tahr in all seasons except autumn, in which they were similar. These results, together with anecdotal evidence from Carneys Creek, suggest that chamois increase their habitat specialization in the presence of tahr. Although differences in habitat selection are likely to have contributed to the coexistence of chamois with tahr, even relatively small increases in tahr density in some seasons could be expected to exclude chamois from some habitats in Carneys Creek.

Male and female Himalayan tahr Hemitragus jemlahicus exhibit extreme sexual size dimorphism and are spatially segregated outside the winter mating season. Segregation results in a greater change in both habitat selection and diet of males relative to females. Since the structure of the ruminant digestive tract is closely related to feeding habit, the rumen morphology of male and female tahr should reflect these apparently important seasonal changes. We therefore hypothesized that the rumen morphology of male tahr would undergo greater change between winter (when the sexes are aggregated) and summer (when the sexes are segregated) compared to females. Samples of rumen wall mucosa were cut from the dorsal rumen wall, atrium ruminis, caudo-ventral blindsac, and the ventral rumen wall of tahr collected during winter (eight male, 10 female) and summer (11 male, 10 female) from the Two Thumb Range, South Island, New Zealand. Although we recorded a significant seasonal increase in the mean surface enlargement factor (SEF) from winter to summer for both sexes, the SEF of females and males were not significantly different in winter (3.88 ± 0.55, SE, and 4.95 ± 0.61, respectively) or summer (7.71 ± 0.55 and 6.86 ± 0.52). We conclude that the effects of inter-sexual differences in habitat selection and diet on rumen morphology were insignificant relative to the extreme seasonal changes in forage quality and quantity that occur in the Two Thumb Range.

Sexual segregation reported in many wild ruminants is generally assumed to result from either different habitat choices by adult males and females or ‘social factors’. In this framework, we studied group composition and habitat use of mouflon sheep (Ovis gmelini) over an annual cycle in the low-mountain range of Caroux-Espinouse (continental France). The analysis of group composition revealed segregation outside the rut, not only between the sexes, but also between the young (2-3 years) and old rams ([ges ] 4 years). Moreover, ewes, young rams, and old rams exhibited some differences in patterns of habitat use in the mid-rutting and lambing seasons, but showed similar patterns in winter and summer. These results, juxtaposed with those of studies of interactions and proximity between individuals within groups, suggest that segregation between age-sex classes has a strong social basis in mouflon sheep.