Age- and sex-related differences in dominance and foraging behaviour of nuthatches Sitta europaea

Nuthatches collecting sunflower seeds from feeders were observed. In summer, but not in autumn, adults collected more seeds per visit than juveniles. From summer to autumn, juveniles increased both the number of seeds collected per unit time and the total number taken per visit. This was probably due to an increase in both experience and ability to handle seeds, possibly associated with beak growth. Males were dominant over females, and adults over juveniles of the same sex. Dominance relations were important in determining the length of visits; males made longer visits. Males also took more seeds per visit. However, females obtained more seeds per unit time, probably to avoid being supplanted by males.     

Sex differences in diet and foraging behavior in white-faced capuchins (Cebus capucinus)

I examined sex differences in diet and foraging behavior in two groups of white-faced capuchin monkeys (Cebus capucinus)in a tropical dry forest at Santa Rosa National Park, Costa Rica. I tested three hypotheses: sex differences in diet and foraging behavior are best explained by (1) sexual dimorphism, (2) the energy demands of pregnancy and lactation for females;and (3) avoidance of competition between the sexes. Sexual dimorphism offered the best explanation of sex differences in the diet and foraging behavior of C. capucinus,accurately predicting that males do more strenuous foraging activity, make less use of small foraging supports, and spend more time on or near the ground. Females spent more time foraging than males did but probably obtained a lower protein yield per unit foraging time. Females exploited more small and embedded invertebrates, while males ate more large invertebrates and vertebrate prey. Pregnant and lactating females spent more time resting and less time foraging than other females did, increasing their foraging return by focusing on foods requiring little handling. There was little evidence of competition avoidance between the sexes.     

Vagabond males and sedentary females: spatial ecology and mating system of the speckled rattlesnake (Crotalus mitchellii)

We used radiotelemetric data and behavioural observations to characterize seasonal (mating versus post‐mating seasons) and sexual variation in movement patterns, as well as to examine some of the ecological factors contributing to the evolution of the mating system in a venomous predator from the Mojave Desert of North America, the speckled rattlesnake, Crotalus mitchellii. Mating occurs in spring from late April to early June, shortly after emergence from hibernation, when snakes are predictably aggregated around the dens. Males and females travelled further per unit time in the mating season compared to the post‐mating season. Males also travelled longer distances per unit time than females in the mating and post‐mating seasons, and males with larger home ranges during the mating season had more potential mating partners. The results obtained suggest that males actively locate females during the mating season, and that the drastic increase in distance travelled by males during the mating season may be caused by strong male–male competition for access to females, probably because of the limited availability of sexually receptive females. Furthermore, males fight for access to females, and males of larger size are more likely to acquire females. Therefore, sexual selection apparently acts on two different male phenotypic traits: investment in mate‐searching activities and male body size. The present study demonstrates that combining quantitative spatial analyses and behavioural observations in an explicit temporal context can significantly advance our understanding of the ecology and evolution of organismal mating systems. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 681–695.     

Female-biased Sex Ratios in the Neotropical Treehopper Umbonia ataliba (Homoptera: Membracidae)

The authors report and explain female-biased sex ratios in the neotropical treehopper Umbonia ataliba Homoptera: Membracidae at Monteverde, Costa Rica. Umbonia ataliba mothers semelparously oviposit egg masses into host-plant branches, make feeding holes, and guard the eggs and the nymphs until the young moult to become adults. At adulthood, offspring sex ratios are female-biased, with families having, on average, one male per 3.17 females (SD = 0.149, n = 48). The female bias does not appear to be explained by the hypothesis that males are more difficult to raise to independence: males are smaller than females, males have a shorter development time, males do not require disproportionately more feeding holes, and males do not experience higher mortality in families that are unprotected from parasites and predators, rather, females die more often in protected families. Thus females, not males, may be more difficult to raise to independence. The authors investigated whether increases in the size of males and females increased the fitness of either sex disproportionately, but found no relationship between size and fitness for either sex. We found evidence that local-mate competition conditions and inbreeding occur. Mating occurs at the natal site and nearly all copulations take place between siblings (99.3 %, n = 153 copulations). Most females (mean proportion of females = 0.65, SD = 0.33, n = 7 families) copulate with their male siblings prior to dispersing; whether the unmated proportion copulates later is unknown. This paper suggests that the numerical bias reflects an investment bias favoured under selection by inbreeding and local-mate competition conditions.     

The maintenance of gynodioecy and androdioecy in angiosperms

Algebraic models of gynodioecy show that the effects on the equilibrium sex ratio of the relative survival and seed production of the sexes and of inbreeding of male-fertile plants are identical for all genic modes of inheritance, provided that different genotypes among male-fertile plants (or among females) do not differ in average fitness. The effects of three modes of inbreeding on equilibrium sex ratios are examined. If there is competition between self- and cross-fertilization of male-fertile individuals, a stable sexual dimorphism can be maintained by an outbreeding advantage of females if both the proportion of cross-fertilized seeds among those borne on male-fertile individuals,t, and the inbreeding depression (fitness inbred/outbred seeds),i, are less than one half. A lower frequency of females is obtained for the same values oft andi if self-fertilization precedes cross-fertilization. If self-fertilization follows cross-fertilization, gynodioecy cannot be maintained by an outbreeding advantage of females. When the sex phenotypes of gynodioecious populations are determined by cytoplasmic inheritance, females need only a slight advantage over males in survival, ovule production or outbreeding to persist at equilibrium. When determined by nuclear genes, androdioecy can be maintained by greater fecundity or a higher survival rate of males than of female-fertile plants, but not by an outbreeding advantage. Androdioecy cannot be maintained with cytoplasmic inheritance of sex. The models suggest explanations for the more frequent occurrence of gynodioecy than of andrdioecy, the high frequency of gynodioecy in Hawaii and New Zealand, and the origin of gynodioecy from hermaphrodite but not from monoecious ancestors.     

Seasonal, sex, and interspecific differences in activity time budgets and diets of patas monkeys (Erythrocebus patas) and tantalus monkeys (Cercopithecus aethiops tantalus), living sympatrically in northern Cameroon

I examined seasonal, sex, and interspecific differences in activity time budgest and diets of patas (Erythrocebus patas) and sympatric tantalus monkeys (Cercopithecus aethiops tantalus) on the basis of 5-day data sets collected in three and two different seasons, respectively, by the method of focal animal sampling. The seasons included species-specific mating and birth seasons. As compared with not only the birth season but also conspecific females, both patas resident male and tantalus male spent less time feeding and more time resting, day and night, in their respective mating seasons. Given that day-resting time includes time for vigilance for non-resident males and receptive females, this may reflect that males should minimize time spent feeding to allow maximum participation in other fitness-increasing activities such as mating-relating activities asSchoener (1971) predicted. In both species, the males consumed fruits containing less protein but more calories and showed a high feeding rate to compensate for the shorter time spent feeding in the mating season. In contrast, females consumed protein-rich food types (i.e. animals, protein-rich seeds, leaves, and flowers) in the birth season to meet the high demand for protein due to pregnancy and lactation. Given that the season for males was considered to be not a calendar but a reproductive “season” (i.e. mating or birth season), both sexes of patas spent more time moving and less time day- and night-resting than did the tantalus counterparts irrespective of the “season”. Patas subsisted on fruits, gums, and supplementarily lipid-rich seeds as an energy source and animal matters and protein-rich seeds as a protein source. In contrast, tantalus subsisted on fruits and lipid-rich seeds as energy and flowers and leaves as protein.     

Hormone accumulation in song regions of the canary brain

[³H]Testosterone (T) was injected into male and female canaries (Serinus canarius), a species in which females are able to sing but do so more rarely and more simply than males. Autoradiographic analysis revealed that males and females have equal proportions of cells labeled by T or its metabolites in four song control nuclei: the high vocal center (HVC), the lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN), the robust nucleus of the archistriatum (RA), and the hypoglossal motor nucleus (nXII). Labeled cells were also observed in both sexes in the medial portion of MAN, and in hypothalamic nuclei. In both sexes, labeled cells in HVC, IMAN, RA, and nXII were larger than unlabeled cells. There were no sex differences in the size of either labeled or unlabeled cells in these song nuclei. The density of labeled cells per unit volume of tissue did not differ between the sexes in any song nucleus analyzed. However, because males have larger HVC and RA than females, males have a greater total number of hormone-sensitive cells in these regions than do females. Comparison of these results with measures of hormone accumulation in zebra finches and tropical duetting wrens suggests that the complexity of song that a bird can produce is correlated with the total number of hormone-sensitive cells in song nuclei. © 1992 John Wiley & Sons, Inc.     

Non-random Mating in the Dance Fly Empis borealis: The Importance of Male Choice

In the dance-fly Empis borealis (Diptera, Empididae), females form swarms to which males, carrying a nuptial gift, come for mating. We examined whether males or females were choosy and/or competed for mates. First, measurements of the size relationships between copulating males and females, nuptial gifts and the swarming females from different swarms were assessed. Second, male visiting time in differently sized female swarms was recorded. Larger (wing-length) females participated disproportionately in copulations in each swarm, but not for the population at large. Female mating status (virgin/non-virgin) or proximity to oviposition (egg size) did not influence the likelihood of copulation. No assortative mating pattern was found: male size and size of nuptial gift did not correlate with size of the mating female. The time spent by males in swarms increased with the number of females present and it took longer when males left a swarm without copulation than when doing so. Male visiting time per female was negatively correlated with number of females in swarms. Males more often left smaller than larger swarms without mating. We conclude that E. borealis males discriminate among females but find no evidence for male competition or for female choice. It is still a question to what degree females compete for males.     

Does time until mating affect progeny sex ratio? A manipulative experiment with the parasitoid wasp Aphelinus asychis

In haplodiploid organisms, unmated or sperm depleted females are “constrained” to produce only male progeny. If such constrained females reproduce, the population sex ratio will shift toward males and unconstrained females will be selected to produce more females. Assuming that a female's own time spent constrained is an index of the population-wide level of constrained oviposition, and that constrained and unconstrained females reproduce at the same rate, the proportion of sons that females produce when unconstrained should decrease with increasing time spent constrained. Alternatively, if females cannot measure time spent constrained or if time spent constrained is not an index to the level of constrained oviposition in the population, the proportion of sons among progeny produced when unconstrained should not depend upon time spent constrained and should be female biased to an extent depending upon the average time spent constrained over evolutionary time. To test these predictions, we manipulated the amount of time spent virgin in the parasitoid wasp Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and measured the number of males and females among progeny produced before and after mating. First, we found no interaction between age and age at mating in their effect on fecundity, which suggests that mating does not change fecundity. Second, we found that females mated at 8 days and 15 days produced equal sex ratios after mating but these were slightly more female biased than the sex ratios of females mated at 1 day. This observed “step response” suggests that females may perceive time from emergence to mating as a discrete rather than a continuous variable (i.e., short versus long), or that females do not perceive time per se but assess their age class (i.e., young versus old) at the time of mating.     

Fighting in fig wasps: do males avoid killing brothers or do they never meet them?

1. In many fig wasp species, armoured wingless males regularly engage in lethal fights for access to females inside figs, which act as discrete mating patches. 2. Kin selection generally opposes killing brothers, because their reproductive success provides indirect genetic benefits (inclusive fitness). However, siblicide may be avoided if (i) brothers do not occur in the same figs, or (ii) males avoid fighting brothers in the same fig. Alternatively, (iii) siblicide may occur because intense mate competition between brothers at the local scale overcomes kin selection effects, or (iv) males do not recognise kin. 3. A fig may also contain wasps from other closely related species and it is not known if males also fight with these individuals. 4. Nine microsatellite loci were used in the first genetic analysis of fighting in fig wasps. We assigned species and sibling identities to males and tested alternative fighting scenarios for three Sycoscapter wasp species in figs of Ficus rubiginosa. 5. Approximately 60% of figs contained males from more than one Sycoscapter species and approximately 80% of fights were between conspecifics, but a surprising 20% were between heterospecific males. 6. Within species, few figs contained brothers, suggesting that females typically lay one son per fig. Overall, most males do not compete with brothers and all fights observed were between unrelated males.     

Reproductive biology and relative male and female fitness in a trioecious cactus,Pachycereus pringlei (Cactaceae)

We describe the breeding system of an autotetraploid trioecious cactus, Pachycereus pringlei, provide estimates of the fitnesses of males and females relative to that of hermaphrodites, and discuss the role played by pollinators in the maintenance of three sexual morphs. Relatively high frequencies of females (45%) and males (26%) exist in coastal desert populations around Bahia Kino, Sonora, Mexico. They differ from hermaphrodites in flower size (females only), initiation of the flowering season, number of flowers produced per night and per season, sucrose content of nectar, and, in females, number of fruits produced per season under open pollination and in response to hand-pollination. Major similarities between the sex classes include overall plant size, nectar volume per flower, percent fruit set in open-pollinated flowers of females and hermaphrodites, seed mass and number of seeds per fruit, and pollen mass per flower in males and hermaphrodites. Hermaphrodites are self-compatible, and the selfing rate is high (65%). Levels of inbreeding depression in selfed fruits and seeds appear to be low. Fruit set is strongly pollinator-dependent in females but much less so in hermaphrodites. Relative fitness of males and females, as measured by annual production of pollen or seeds, is at least 1.5 times higher than that of the corresponding sex function in hermaphrodites. Given the high selfing rate and apparent lack of inbreeding depression, these fitness differences are insufficient to explain the occurrence of trioecy in this species.     

Courtship Activity of Wandering and Burrow-holding Male Uca arcuata

The male of Uca (Deltuca) arcuata, a vertical claw-waving fiddler in the Indo-Pacific, is used to court females by approaching them from his burrow or while wandering. Differences in the rate of encounters with females between burrow-holding males and burrowless wandering males are found not to be significant. Burrow-holding males less often cause displacement of wandering by females than wandering males do. Wandering of females caused by wandering males occurs as often as wandering of males caused by other males. Thus, burrow-holding males tend not to reduce the number of their potential mates in the neighborhood. Burrow dwelling males are apt to start wandering after decreased encounters with females. Wandering males experience more interactions with other males than burrow-holding males do. Most wandering males that displace burrow owners descend the burrows one or more times after displacing the owners. The extra fighting for temporary burrows is responsible for no increase of the encounter rate with females during wandering.     

RESOURCE COMPENSATION AND THE EVOLUTION OF GYNODIOECY IN PHACELIA LINEARIS (HYDROPHYLLACEAE)

Gynodioecy is a dimorphic breeding system in which hermaphrodite and female individuals coexist in populations. Theoretical models have shown that if nuclear genes control sex expression, then gynodioecy can evolve only when females have large advantages in one or more fitness components. These female advantages must be large enough that females' expected lifetime production of viable seeds is more than twice that of hermaphrodites. Previous studies have found that cytoplasmic inheritance and/or a large offspring-vigor advantage of females (caused by hermaphrodite self-pollination and inbreeding depression of selfed seeds) account for this breeding system's evolution. This paper reports studies of gynodioecy in Phacelia linearis, an insect-pollinated annual plant in which gender inheritance appears to be nuclear. Twenty-six P. linearis populations surveyed in northern Utah, USA, contain a majority of perfect-flowered hermaphrodites, but most (22) also contain male-sterile individuals (females), at frequencies of up to 0.16. The hermaphrodite selfing rate is low (0.00–0.20 in four populations). Maternal gender does not consistently affect components of offspring vigor, such as seed size, germination rate, seedling survivorship, and vegetative size. Plants of the two genders do not differ in number of seeds per fruit or mean seed mass. Females produce significantly more fruits and seeds than hermaphrodites in natural populations. The ratio of the mean lifetime seed production of females to the mean lifetime seed production of hermaphrodites ranged from 1.31 to 2.52 in six natural populations. Females have greater shoot biomass than hermaphrodites and produce more seeds at any given shoot biomass than hermaphrodites, suggesting that their seed-production advantage arises from gender-specific patterns of resource allocation to growth and reproduction. The gender difference in plant size varies across environments and across genetic backgrounds. In this species nuclear gynodioecy appears to be evolutionarily stable mainly because of resource compensation by females, without a large outcrossing advantage of females.     

Ant eating behavior of mountain gorillas

Eleven cases of feeding on driver ants (Dorylus sp.) by mountain gorillas (Gorilla gorilla beringei) are described. Ant eating provides the gorillas with more animal protein and other nutrients per unit feeding time than do other forms of insectivory that contribute to their diet, but it is so rare that it is unlikely to be of real nutritional significance. Gorillas obtain ants with their hands and do not use tools. Immature individuals (except infants) ate more ants than did adult females, and silverbacks were not seen to eat ants. These differences are more likely to reflect differences in individual taste and interest in novelty than differences in nutritional strategy. Not all gorillas in the Virungas population eat ants. Intra-population variability may be ecologically contingent, but ant eating appears to be a socially acquired and transmitted taste.     

Protandry and postandry in two related butterflies: conflicting evidence about sex-specific trade-offs between adult size and emergence time

Natural selection acting on timing of metamorphosis can be sex-specific, resulting in differences in timing between males and females. Insects with discrete generations frequently show protandry: males usually mature before females. Both Euphydryas editha and E. aurinia butterflies followed this trend. The present study was motivated by the unusual observation of consistent postandry in addition to protandry. In a single E. editha population observed over 20 years the emergence period of males was longer than that of females, both the first and last emerging individuals being males. Variance of timing among individual E. editha larvae is imposed by spatial patchiness of the snowmelt that releases them from winter diapause. If individual larvae released late from diapause were to compensate for their lateness by shortening their development times, they would be small at maturity. If such compensation were only partial, they would be both late and small. Size and timing would become associated. If females were more prone to such partial compensation than males, the observations of postandry could be explained and the prediction made that any tendency for late individuals to be small should be stronger in females than in males. This was the case: in 1 year late males were the same size as early males, in a second year they were larger. Late females were significantly smaller than early females in both years. In E. aurinia, results were opposite both to theoretical prediction and to the observations from E. editha: although the male emergence period was longer than that of females exactly as in E. editha, late males were smaller than early ones, while late females were not small. The data from E. editha support the hypothesis of a sex-specific trade-off between size and emergence time, the data from E. aurinia do not.     

Vigilance behavior during the birth and lactation season in naturally occurring ring-tailed lemurs (Lemur catta) at the Beza-Mahafaly Reserve,Madagascar

I examined the vigilance behavior of adult males and females in two groups of ring-tailed lemurs(Lemur catta)during the birth and lactation season at the Beza-Mahafaly Reserve, southwestern Madagascar. I found no sex difference with respect to the rates of overall vigilance, rates of vigilance toward a potential predator or unfamiliar sound, or rates of vigilance toward conspecifics from other social groups, nor were there sex differences in the percentage of time spent vigilant in any of the above categories. Higher-ranking females were vigilant significantly more often toward predators or potential predators than lower-ranking females were. I detected no relationship between vigilance behavior and dominance rank among adult males. The alpha female in each group exhibited significantly more vigilance behavior than all other members of her group. It was predicted that males should exhibit more vigilance behavior than females do, particularly during the birth and lactation season, when predator pressure is high, if they are benefiting females in this respect. I discuss the results in the context of this prediction and in terms of how ring-tailed lemur males benefit females, and why they may be tolerated in social groups.     

Males of the two-spotted spider mite attempt to copulate with mated females: effects of double mating on fitness of either sex

In Tetranychus urticae (Acari: Tetranychidae), when the intervals between first and second copulation are more than 24 h, only the first copulation is effective for females. Therefore, adult males should copulate only with virgin females, but not with females that copulated more than 1 day ago. Indeed, T. urticae males preferred virgin females to mated females under dual choice conditions. In the absence of virgin females, however, 60% of males copulated with mated females (n = 30). Therefore, the effects of male copulation behaviour on male and mated-female fitness were examined, respectively. Since T. urticae is arrhenotokous (i.e., only daughters have genes derived from their father), the proportion of females among the offspring was used as an index of male fitness. After males had lived with/without a mated female, the males were allowed to copulate with a virgin female. The proportion of females among the offspring did not differ between males with and without a female. On the other hand, when mated females lived with an adult male, their egg production was lower than mated females without a male. These results suggest that males do not seem to obtain fitness benefit from the copulation behaviour and that mated females incur a fitness cost due to the male behaviour.     

Different rewards in female and male flowers can explain the evolution of sexual dimorphism in plants

Insects use floral signals to find rewards in flowers, transferring pollen in the process. In unisexual plants, the general view is that staminate (male) and pistillate (female) flowers obtain conspecific pollen transfers by advertising their rewards with similar floral signals. For female plants lacking food rewards, this can lead to floral mimicry and pollination by deceit. In this study, we challenge this view by presenting evidence for different rewards offered by flowers on females and males, as a mechanism promoting sexual dimorphism in Leucadendron xanthoconus (Proteaceae), a clearly sexually dimorphic shrub. The tiny beetle pollinators Pria cinerascens (Nitidulidae) depend entirely on the plants they pollinate for survival and reproduction. Male flowers provide mating and egglaying sites, and food for adults and larvae. Female flowers lack nectar and function to shelter pollinators from rain. Their flower heads have cup‐shaped display leaves, and are more closed than are those in males. On rainy days, flowers on females received 30% more visits than did flowers on males, and 90% more than they did on sunny days. When we removed display leaves in females, intact flower heads received 14 times more P. cinerascens visits than did manipulated flower heads, indicating that the cup shape attracts the beetles. In both sexes, having many flowers increased the probability of visits and the number of P. cinerascens visiting a plant. In males, the number of larvae was positively correlated with floral‐display size, while in females, seed set (pollen transfers) showed no relationship with floral‐display size. Ninety‐five per cent of the ovules received pollen and 52% matured into seeds. We explain the sexual dimorphism in L. xanthoconus as a result of an intimate partnership with P. cinerascens pollinators, in conjunction with a rainy climate. Pollinators favour large male floral displays, because they offer a reliable food source for adults and larvae. Frequent rains drive the P. cinerascens to leave males in search of the protection offered by females. Because females offer shelter, an essential resource that is not offered by male plants, they receive sufficient pollen independent of their floral‐display size. This pollination system promotes the evolution of sexually dimorphic floral signals, guiding pollinators to different rewards in male and female flowers. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 97–109.     

Biology of Leipothrix dipsacivagus (Acari: Eriophyidae), a candidate for biological control of invasive teasels (Dipsacus spp.)

The present study describes key aspects of the biology of Leipothrix dipsacivagus, an eriophyid mite that is under study as a biological control candidate of Dipsacus fullonum and D. laciniatus (Dipsacaceae). Preliminary host-specificity tests have shown that it can develop and reproduce only on Dipsacus spp. (teasels). Studies were conducted in a laboratory at 26 ± 2^oC with 16 h of light per day. Mites for the stock colony were collected from D. laciniatus in Klokotnitsa, Bulgaria and reared on rosettes of D. laciniatus in the laboratory. Unfertilized L. dipsacivagus females reared in isolation from the juvenile stage produced male offspring only, while progeny of fertilized females were of both sexes, suggesting arrhenotokous parthenogenesis with haplodiploid sex determination. Experiments were designed to compare male progeny from fertilized females to males from unfertilized females and to compare males and females from fertilized females. Male progeny of virgin mothers had significantly longer durations of active immature stages and total egg-to-adult period than male progeny of fertilized females. Female progeny had significantly longer durations of egg incubation, active immature stages and egg-to-adult period than male progeny from fertilized mothers. Adult longevity was significantly greater in females than in males. Fertilized females produced significantly more eggs per day and overall than virgin females. The results of this study suggest that fertilization status of L. dipsacivagus females can affect both their own fecundity and the development of their male progeny.     

Burrow architecture and digging activity in the Cape dune mole rat

While females are traditionally thought to invest more time and energy into parental care than males, males often invest more resources into searching and displaying for mates, obtaining mates and in male–male conflict. Solitary subterranean mammals perform these activities in a particularly challenging niche, necessitating energetically expensive burrowing to both search for mates and forage for food. This restriction presumably affects males more than females as the former are thought to dig longer tunnels that cover greater distances to search for females. We excavated burrow systems of male and female Cape dune mole rats Bathyergus suillus the, largest truly subterranean mammal, to investigate whether male burrows differ from those of females in ways that reflect mate searching by males. We consider burrow architecture (length, internal dimensions, fractal dimension of tunnel systems, number of nesting chambers and mole mounds on the surface) in relation to mating strategy. Males excavated significantly longer burrow systems with higher fractal dimensions and larger burrow areas than females. Male burrow systems were also significantly farther from one another than females were from other females' burrow systems. However, no sex differences were evident in tunnel cross-sectional area, mass of soil excavated per mound, number of mounds produced per unit burrow length or mass of soil excavated per burrow system. Hence, while males may use their habitat differently from females, they do not appear to differ in the dimensions of the tunnels they create. Thus, exploration and use of the habitat differs between the sexes, which may be a consequence of sex differences in mating behaviour and greater demands for food.