The intensive study of the Arctic skua (Stercorarius parasiticus) population on Fair Isle has provided an example of the maintenance of a stable polymorphism by sexual selection in conjunction with assortative mating (O'Donald, 1983). We tested several of O'Donald's hypotheses using data collected from the large colony of Arctic skuas on Foula. There was some evidence for assortative mating of the phenotypes but this did not confer any short-term fitness advantage. In contrast to the situation on Fair Isle, we found little indication that sexual selection took place for dark males since no differences in timing of breeding or productivity were evident between the two male phenotypes in new partnerships. Nor could we detect variation in adult body size, body condition, or any life-history characteristic between melanic and pale birds of either sex. Many of the selection pressures documented on Fair Isle appear to be absent at the neighbouring Foula, despite a fair degree of gene flow between these colonies. The frequency of pale adults on Foula and in Shetland as a whole has declined since the 1970s, indicating that currently directional selection may be favouring the melanic phenotypes at the southern end of the breeding range.

We examined data on live-captured polar bears (Ursus maritimus) from western Hudson Bay relative to differential maternal investment and facultative sex ratio theory. In spring, shortly after den emergence, we found no differences in mass or body length of cubs in litters of one or two. In triplet litters captured in spring, male cubs were larger than females in both mass and body length, possibly due to sibling competition for limited maternal resources. In cubs captured during autumn, sex-based differences in mass and body length were found only in litters of one with males larger than females. Yearling males captured in autumn were heavier and longer than females in litters of one and two. In twin litters of one male and one female cub in spring and autumn, we found no differences in mass or body length. Except singleton female cubs in spring and female and male triplets in spring, cub and yearling mass were correlated with maternal mass. Mothers with singletons in spring were more likely to have male cubs but, in general, there was little evidence to suggest that mass or age of mothers influenced offspring sex. Litter size, maternal mass, and maternal age all influenced cub and yearling size, but offspring sex was less important. Results suggest that female polar bears do not normally invest differentially between offspring of different sexes except in triplet litters in spring.

The male reproductive cycles of three species of vespertilionid bat (Nyctophilus geoffroyi, N. major and Vespadelus regulus) are described. Descriptions are based on the degree of testicular and cauda epididymal development estimated from field captures, and for N. geoffroyi, on histological examination of fixed specimens and assays of their testicular testosterone concentrations. All species were found to undergo a dissociated pattern of reproduction; the activity of the testes and accessory glands of reproduction were asynchronous. Spermatogenesis occurred in summer/early autumn (December–March) and testes generally regressed before mating began in autumn (March–May). Spermatozoa were stored in the cauda epididymides during the mating period. Leydig cells of N. geoffroyi involuted prior to mating but the prostate gland remained enlarged and secretory during winter (June–August), regressing in late spring (November). Testicular testosterone concentrations were greatest when Leydig cells were maximally enlarged, and concentrations were low during the mating period. The reproductive cycle of all species apparently involved asynchrony between primary and secondary sexual function, which is typical of vespertilionid bats inhabiting temperate latitudes. As mating occurs when sperm stores cannot be replenished, selection for prudent sperm allocation may be expected.

Density-dependence in juvenile survival may be difficult to detect if survival is also affected by density-independent factors. We investigated the relationships among weather parameters, population density, and lamb survival of bighorn sheep with long-term data from a marked population where we manipulated population density. We distinguished neonatal survival and winter survival. Density interacted with weather variables to affect neonatal survival; spring and winter temperatures had a positive effect on neonatal survival only when population density was high. Neonatal survival was positively affected by spring precipitation independently of population density. Winter survival was positively correlated with temperature and precipitation during the previous spring, negatively correlated with density, and independent of winter temperature or snowfall. The effect of weather on lamb winter survival did not vary with density. Bighorn lambs are well adapted to harsh winter weather, but spring weather influenced survival of lambs at birth and during the subsequent winter, possibly through its effects on forage availability. Our study clearly demonstrates density-dependence in lamb survival. Some of the effects of weather on lamb survival are density-independent, others are mediated by an interaction with population density.

When prey availability depends on water depth, a diver should choose an optimal depth for foraging. A model that predicts the optimal foraging depth for a diver is presented in this paper. General predictions derived from the model are: (1) optimal foraging depth is always shallower than the depth at which prey density is the highest, even if the depth of the highest prey density is within easy reach; (2) a larger diver should make deeper and longer dives and stay longer on the surface than smaller divers for optimal foraging; (3) foraging efficiency of larger divers is not always greater than smaller divers, although the larger divers forage at the depth of higher prey density. These predictions, derived from the model, are consistent with the comparative studies of diving behaviour in marine birds.

The annual cycle of testes weight of adult male rabbits (Oryctolagus cuniculus) was studied in three populations on the sub-Antarctic Kerguelen archipelago during 1984–85. This study was completed in April 1987 with an analysis of differences in diet quality between populations, assessed by the proportion of nitrogen and lignin in stomach contents. A marked annual cycle of testes weight was observed in all populations, with a rapid fall in testes weight from February to March. As in most rabbit populations studied elsewhere, testes growth resumed immediately in two populations (called Morne and Molloy). In contrast, testes growth was deferred by five to six months in the third population (Armor), subject to harsher environmental conditions. Moreover, a larger proportion of the Armor males had inactive testes during the reproductive season. The diet of the Armor population was characterized by low nitrogen and high lignin content, suggesting poor-quality diet as an immediate cause of deferred testes growth. We propose that reduced testes size during adverse conditions might be adaptive by increasing survival probability through reduction of basal metabolism and limitation of agonistic and reproductive activities, behaviours which are costly in terms of high energetic expenditure. However, at the population level, the timing of the breeding season was not related to the cycle of male testes weight and thus seems to depend on females' condition.

A viviparous hoplonemertean, Prosorhochmus chafarinensissp. nov., is described from the Chafarinas Islands (western Mediterranean). The species lives in the low eulittoral under the encrusting alga Lithophyllum lichenoides. Prosorhochmus chafarinensis is compared and contrasted in detail with the other valid members of the genus, P. claparedii from European waters, P. americanus from South Carolina, and P. adriatica from Italy.

The occurrence of large individuals in fluctuating populations of microtine rodents (the Chitty effect) has received considerable attention. Recent studies showed that there are no causal relationships between the Chitty effect and the multi-annual population cycles of voles and lemmings. We studied five populations of Microtus duodecimcostatus in southern France with capture-recapture methods. Mean body mass was constant in all populations. Maximum observed body mass was more variable, and slightly positively correlated with density, except in the most fluctuating population where the correlation was strong. A careful study of the occurrence of large voles in these populations showed that most were pregnant females, and that the few large males were present when density was high and sample sizes were large. Comparison with published studies indicates that the Chitty effect, though not restricted to microtines, is not a general phenomenon in small mammal populations. Our field results and laboratory data on the same species suggest that M. duodecimcostatus has a determinate body growth, contrary to some Microtus species which have an indeterminate growth.

The loss of tooth effectiveness due to molar wear has been proposed as an important cause of mortality in ungulate populations. Voluntary intakes, digestibility, mean retention times, chewing behaviour (during eating and rumination), and diet selection (physical selection: short vs long particles in hay; and botanical selection: leaf vs stem) were compared in two groups of female red deer (Cervus elaphus) which differed in molar occlusal surface area, in order to test the hypothesis that behavioural and physiological mechanisms can be used to maintain assimilation efficiency in the presence of low functional tooth effectiveness. The group with lower values for first lower molar occlusal surface area (OSA) corrected for body weight had lower voluntary food intakes (P = 0.0126). The low OSA group had a greater number of chews per g DM of food ingested (P = 0.0167), a greater time spent chewing (P = 0.0476) but a lower number of chews per min than did those with a high OSA (P = 0.0484). The total number of chews per day was similar for both groups (P = 0.2011). The number of ruminating chews per day was less for the low OSA group (P = 0.0377). The group with low OSA values had a larger average particle size in their faeces (P = 0.0346). No differences were detected between groups in the physical or botanical composition of the diet selected (P = 0.3030, P = 0.3056, respectively) or in total digestibility and mean retention times (P = 0.1357, P = 0.3464, respectively). As a consequence of the lower voluntary intake the low OSA group had a lower digestible dry matter intake (P = 0.0170). This study supports the view that intake modification and the time invested in chewing during eating are the main mechanisms used to compensate for reduced chewing effectiveness associated with changes in tooth morphology, although the compensation is not total.

Morphological and isozyme variations between 13 populations of the species hitherto named Patella granularis were investigated to see whether differences in shell structure between the west coast versus the south and east coasts of southern Africa are supported by other morphological features or by genetic differences. The shells showed a definite decrease in size from west to east, but this is correlated with productivity and is of no diagnostic use in distinguishing between populations. Discriminant functions analysis based on shell morphometrics failed to separate populations from the three coastal regions. Shells from the northern east coast do, however, have shell nodules with a dark pigmentation, distinctly separating them from those further south and west. No differences in radular or soft part morphology were detected between the populations, but the four northernmost populations on the east coast have a significantly shorter Z looping of the gut than the other populations along the coast. Significant microstructural differences in the sperm were also detected between these two groups of populations. Electrophoretic analysis of 16 enzyme loci failed to detect any significant differences between the west and south coast populations, but revealed a genetic identity (Nei) of 0.528 as well as four diagnostic alleles between the four northernmost populations from the east coast compared with those to the south and west. The two genetically distinct forms occurred sympatrically at one of the study sites on the east coast (Coffee Bay). It was concluded the two groupings were sufficiently different to warrant the recognition of a separate species, which is centred in KwaZulu-Natal on the east coast and extends south to Coffee Bay, from where it is replaced by P. granularis. There is, however, no evidence at all that the west coast populations are in any way separable from the remaining populations of P. granularis on the south coast.

Reproductive correlates and fitness consequences (survival, recruitment) of variation in the incubation onset of pied flycatchers (Ficedula hypoleuca) were studied across 4 years in a southern European population, where between 36 and 89% of the females started to incubate with the penultimate egg or earlier. Females started to incubate up to 3 days before completing their clutches, this being accompanied by hatching spread. Females who advanced incubation before completing the clutch tended to be in better condition and to lay larger clutches than those that postponed incubation until the clutch was complete. Although laying date had no effect on onset of incubation, the effect of clutch size was much more marked when the influence of laying date on clutch size was controlled. Females who started to incubate earlier fledged more young than females delaying incubation but their higher fledgling success was unrelated to recruitment. Females starting to incubate with the last egg had fewer fledglings but of larger size, higher mass, and in better condition than females who advanced the incubation. Female survival to the next breeding season did not differ between those that started incubation before clutch completion and those that did not do so, but an advanced onset of incubation by females was related to higher mortality of their pair mates. Females that increased the size of the clutch with respect to the previous year tended to incubate their eggs earlier, while those whose clutch size did not change or was lower started incubation at about the same stage they did the year before. This trend was apparently influenced by improvements in body condition. Clutch size may constrain onset of incubation through environmental or genetic correlations, which are likely to be mediated by hormones. It is proposed that, in this population, an early onset of incubation in pied flycatchers does not affect reproductive fitness in most circumstances.

We describe the most westerly known maternity colony of Nathusius' pipistrelle bats (Pipistrellus nathusii). The bats were identified by using morphometric measurements and analysis of time-expanded echolocation and social calls. The roost, containing approximately 150 individuals, was located in a mid 19th century farm stable block and store house situated in parkland in County Antrim, Northern Ireland. The roost was visited on 30 April, 1 May and 22 June 1997. Over this period, 11 bats were caught: one adult male, five pregnant females, four lactating females and a juvenile male. Direct observation of behaviour patterns suggests that mating groups of P. nathusii may occur in Ireland as late as May. The migratory nature of this species is discussed.

Scent-marking behaviour and inter-pack aggression were studied in wild Ethiopian wolf, Canis simensis, packs. Raised-leg urinations, followed by ground scratching, were the most frequently deposited scent-mark. Scent-marking rates were highest along or near territory boundaries, where distances between scent-marking sites were reduced and the proportion of multiple marks was increased, relative to other areas. Marking rates increased with wolf numbers during patrols but not during other activities. Although all adult members of a pack contributed to scent-marking, the dominant pair marked most frequently. Subadult males scent-marked occasionally but subadult females never did. Wolves vigorously over-marked neighbours' scent-marks. Most direct encounters between neighbouring wolves at territory borders were aggressive and involved repeated chases, and the larger group was most likely to win. Resident wolves were more tolerant of opposite-sex than same-sex neighbours. Resident wolves therefore signalled pack composition and status at home range borders by olfactory and auditory cues and by aggressive contests. Such signalling may reduce the occurrence of potentially costly inter-pack aggressive encounters at territory borders and provide information on reproductive status.

The arterial supply to the eyes and brain of the common thresher shark, Alopias vulpinus, was examined and compared with that of five other lamniform shark species. Temperatures of the eyes and brain in two of these species were shown in previous studies to be higher than ambient. This was considered to be correlated with the presence of an orbital rete mirabile derived from the hyoidean efferent and pseudobranchial arteries. This study shows that the pseudobranchial artery forms a rete in only one of the two species previously shown to be warm, indicating that the brain of the other species is warmed by a non-retial vessel. This finding raises the possibility of brain and eye warming in Alopias vulpinus, which lacks an orbital rete mirabile.