It is an axiom of science that, in order to measure a process, one ends up changing it in some way. This has been apparent to physicists for a long time but it is perhaps less apparent as a consideration in the biological literature. In many cases the degree to which one changes the process that is being measured is insignificant but there are exceptions. This problem becomes particularly difficult in wildlife biology when one is sometimes faced with gaining information from and protecting small populations of endangered animals. The combination of small sample size, and the high value of each individual to the population, mean that any interference could have negative consequences for the population. The resulting data from the study may have statistical characteristics that make it very difficult to use as a basis for conclusive results.

We have read with interest the paper by Alibhai, Jewell & Towindo: Effects of immobilization on fertility in female black rhino (Diceros bicornis) (J. Zool. Lond. (2001). 253: 333--345). As conservation professionals who have devoted our careers to serving the needs of endangered species while employing only the highest standards of veterinary care, we feel it necessary to point out that Alibhai, Jewell & Towindo's experimental design, selection of data for analysis, and basic conclusions may be flawed in several critical ways.

We appreciate the concerns of Atkinson et al. regarding our paper (Alibhai, Jewell & Towindo, 2001), and will try to give reassurance that these are unfounded.

With regard to the drugs used, Atkinson et al. are incorrect in stating that all the agents used in combination with M99 were alpha-2 adrenoceptor agonists. Azaperone is a butyrophenone neuroleptic sedative (Hall, Clarke & Trim, 2001). Whether ACP or another sedative agent was used in combination with etorphine hydrochloride, the risks we have discussed remain valid since the most potent and potentially dangerous is the opioid etorphine, which is used for wildlife immobilization in a high dose to produce an anaesthetic rather than analgesic effect (Branson, Gross & Booth, 1995). The stresses involved in the capture circumstances are very likely to carry a further risk for the pregnant rhino.

Over the past 50 years European populations of the lesser horseshoe bat Rhinolophus hipposideros have severely declined, probably because of the loss of foraging habitat. To date, studies of the foraging behaviour of this species have been limited as its low mass (4–8 g) precluded the use of radio-telemetry because commercially available radio-transmitters exceeded 10% of its body mass. In this study, radio-transmitters weighing < 0.35 g were built. These increased the body mass of the animals from 4.5% to 8.1%, with no demonstrable adverse effect on their flight behaviour. The habitat selection of eight female lesser horseshoe bats was studied in Monmouthshire, U.K. The bats had foraging ranges between 12 and 53 ha (100% kernel). Although one bat foraged 4.2 km from the roost, for 50% of the time tracked bats were recorded within 600 m of the nursery roost. The estimated density within 200 m of the roost was 5.8 foraging bats/ha. This decreased to 0.01 bats/ha at 1200 m. Compositional analysis revealed that this species used woodlands, predominately broadleaf, more than any other habitat. In addition, the bats foraged in areas of high habitat diversity. Conservation management of this species should concentrate on such areas within 2.5 km of the nursery roost.

Spatial distribution of a deep-sea crinoid Pentametrocrinus tuberculatus was investigated in the Izu-Ogasawara Arc, western Pacific. Photographic and video recordings coupled with direct visual observations were conducted from the manned submersible Shinkai 2000 between the depths of 1340 and 1840 m on the south-western slope of the An'ei Seamount (29° 15'N, 138° 37'E). Close to the seabed, temperature, salinity and dissolved oxygen concentration were in the range of 2.2–3.1 °C, 34.38–34.52 and 1.40–2.15 ml l−1, respectively, and the bottom substratum consisted mainly of flat-surfaced lava rocks covered by thin manganese oxide crusts. Pentametrocrinus tuberculatus individuals were attached to the surface of lava rocks with their five arms extended horizontally and showed no recognizable movement. Incidence of arm loss (which may indicate mechanical damage or predation pressure) was very low. The highest density of P. tuberculatus occurred in an area termed ‘terrace’ where the slope was reduced above a relatively steep hillside. Analysis of nearest neighbour distances showed that P. tuberculatus individuals generally demonstrate regular spacing with either no or partial overlap of their ambits (= circular area defined by the extended arms), due to a combination of aggregative tendency (to form patches) and behavioural spacing among individuals within a patch. The observed pattern of distribution was clearly different from the pattern expected from random occurrence of individuals in space. Thus, on spatial scales of 101 to 103 m, P. tuberculatus showed a contagious or aggregated distribution, while on smaller scales and in areas where crinoids were concentrated they showed a combination of patch formation and regular distribution of individuals.

Through interspecific hybridization and subsequent backcrossing, genes and genomes may be transferred over the species barrier. In Sweden, the introduced brown hare Lepus europaeus hybridizes with the native mountain hare L. timidus. To investigate the direction and the extent of transfer of mitochondrial DNA (mtDNA) between the species, the mtDNA haplotypes were screened in 522 brown hares and 149 mountain hares from areas of sympatry and allopatry. A total of 51 brown hares with mountain hare mtDNA, but no mountain hares with brown hare mtDNA were detected. Thus, mtDNA transfer over the species barrier is directed from mountain hares to brown hares. We argue that frequency-dependent hybridization and/or interspecific male competition mediates this directionality. Further, the percentage of brown hares with transmitted mountain hare mtDNA was lower in areas of former species sympatry (0.6%) compared to areas of current sympatry (15%). Thus, the transferred mtDNA may disappear from brown hare populations if there is no continuous input through hybridization. We suggest that specimens with an alien mtDNA experience a fitness reduction as a result of a functional incompatibility between the cytoplasmic mitochondrial genomes and the cell nucleus.

Senescence is the internal physiological deterioration that accompanies advancing age. Evolutionary hypotheses predict that rates of senescence should vary directly with extrinsic mortality and inversely with fecundity. If so, naked mole-rats (Heterocephalus glaber) should live a long time (senesce slowly) because in nature they inhabit heavily protected burrows, and large, old breeding females make disproportionate reproductive contributions. In addition H. glaber has an exceptionally low metabolic rate, which may reduce oxidative stress. We have maintained naked mole-rats in captivity since 1974. Here we report that individuals can live a very long time: many are alive after more than 20 years and some are 26 years old (and counting). Although we do not yet know how long naked mole-rats can live, they already are older than the maximum longevity of all but one of 156 rodent species that have been maintained in captivity from birth to death.

This study assesses the pattern of occurrence of a generalist species, the Eurasian badger Meles meles, in forest fragments located in agricultural landscapes of central Spain with a coarse-grained pattern of fragmentation (<20% forest cover in the landscape). Four forest regions (n = 139 forest fragments) were sampled. Badger presence/absence in forest fragments was studied in relation to: forest size, isolation and vegetation structure. Badgers were tested to see if, despite their habitat generalism, they were negatively affected by forest fragmentation in this type of fragmented landscape. Results indicated a strong and significant effect of fragment size on badger occurrence (presence was rare in forest fragments <100 ha) and an important effect of isolation at a local scale. The response of badgers to forest fragmentation in Spain is quite different to the response in other European landscapes. In Spain, badgers cope with a divided coarse-grained landscape where suitable habitats are embedded in a largely unsuitable matrix (cereal croplands). In contrast, in Britain or central Europe, badgers may be benefited by forest clearances in a heterogeneous but non-divided landscape where small woodlots are separated by a matrix of good quality (mainly pastures) and fragmentation produces fine-grained mosaic landscapes where food and den sites are simultaneously enhanced. Species' response to forest fragmentation may strongly depend on the pattern of fragmentation and, in coarse-grained fragmented landscapes, generalist species may be affected in the same way as specialist ones.

In response to the interplay between variation in food quality and energetic demands, the foraging behaviour of captive green-backed firecrown hummingbirds Sephanoides sephaniodes was studied. Hummingbirds were exposed to two temperatures (25°C vs 15°C), two food qualities (0.5 vs 0.75 m sucrose solutions), and two costs of feeding (birds were provided with feeders with and without a perch). Food selection and consumption were measured, as well as time budgets and metabolic rate while feeding. We predicted that when given a choice, birds would minimize the cost of feeding by selecting feeders with a perch and with a high sugar concentration. However, rather than increasing energy consumption when energy availability was low and thermoregulatory demands were high, hummingbirds remained perched. They reduced feeding and spent most of their time perching. Our results identify a novel behavioural and physiological strategy in hummingbirds. These birds seem to shift their foraging behaviour depending on thermoregulatory and feeding costs. When these costs are high, rather than matching them with increased energy consumption, hummingbirds reduce energy costs by reducing activity. They seemed to adopt the following strategy: when food quality was high and thermoregulatory demands were low, they adopted a high-expense lifestyle. In contrast, when thermoregulatory costs were high, they adopted an energy conserving strategy even when food quality was high. We hypothesize that limitations imposed by physiological processes may explain why animals do not forage during all available time and why under some circumstances they choose foraging behaviours with lower rates of net energy gain.

We tested the hypothesis that the number of presacral vertebrae in lacertid lizards has evolved to meet requirements set by the structural habitat. The idea was that lizards from cluttered habitats (densely vegetated areas, stony walls and hills, rocks) would be aided by a flexible backbone with many vertebrae, ensuring manoeuvrability, whereas lizards from open habitats would require stiffer vertebrate columns, with relatively few vertebrae, favouring speed and acceleration capacity. In contrast to earlier findings in fishes and snakes, evolution of vertebral number and body size was uncorrelated in lacertid lizards. Body size also did not differ between structural habitat types (open areas, densely vegetated areas, vertical elements). Traditional analysis of variance suggests strong differences in vertebral counts between species from open areas and cluttered areas, the latter having higher numbers of presacral vertebrae. When adequate phylogenetic analyses are used, differences remain significant although the level of significance is considerably lower. Tests of the mechanistic relationships between vertebral number, bending ability, and manoeuvrability, and assessment of the relative importance of manoeuvrability and speed in habitats with varying degrees of impediment are needed to reveal the evolutionary path that has led to the differences in vertebral number.

Time-depth recorders were used to investigate the diving performance and behaviour of two bimodally respiring turtle species, Rheodytes leukops and Emydura macquarii, known to have a high and low reliance on aquatic respiration, respectively. Significant differences in diving performance between R. leukops and E. macquarii were observed in the number of dives/day (39.3±5.38 vs 112.2±11.73 dives/day; mean±se), mean dive length (33.1±7.33 min vs 9.6±2.26 min) and maximum dive length (623±104.74 min vs 67.1±8.14 min), respectively. Differences in diving performance between R. leukops and E. macquarii are attributed to the species' reliance (or lack thereof) upon aquatic respiration. Rheodytes leukops displayed a weak bimodal pattern of increased surfacing frequency in the early morning (05:00–07:00) and late afternoon (14:00–18:00), while E. macquarii displayed a strong bimodal pattern of elevated surfacing frequency over similar time periods. Daily patterns of increased surfacing frequency for both species failed to correlate with fluctuating aquatic Po2 levels or water temperature, and may instead be explained by the heightened activity levels of both species during twilight.

Miniature radio-transmitters were used to follow movements over a 10-day period of the 10 g honey possum Tarsipes rostratus, and the areas covered were compared with home-range estimates calculated from long-term mark-and-recapture records using pitfall traps. The study was carried out in the Scott National Park, in the extreme south-west of Western Australia, and shows that honey possums may move far greater distances than is apparent from trapping records. The overall mean area used determined by radio-tracking was significantly larger at 0.54±0.19 ha than the apparent home range of 0.03 0.01 ha determined by trapping. The area used by males was significantly greater than that of females when measured by radio-telemetry (0.79±0.24 ha vs 0.14±0.08 ha, P = 0.058), but did not differ significantly when estimated from trapping records (0.03±0.01 ha vs 0.01±0.01 ha). These data suggest that honey possums frequent plant assemblages at night where they are vulnerable to pitfall trapping, but that males, particularly, spend the day in other areas that may be as far as 200 m distant.

Metabolizable energy intake and changes in body mass was measured in the desert gerbil Gerbillus dasyurus when parasitized by the flea Xenopsylla ramesis. We hypothesized that energy requirements for maintenance, or average daily metabolic rate, of parasitized gerbils would be higher than those of non-parasitized gerbils. We also hypothesized that the efficiency of utilization of energy for maintenance would be the same for parasitized and non-parasitized gerbils, as this measurement is dependent mainly on dietary quality. Fifty fleas feeding on a gerbil consumed 3.68±1.19 mg blood, in total. This amounted to 34.3±1.8% of body mass of a starving flea and only about 0.17% of the blood volume of the host. The absolute amount of blood consumed by X. ramesis is the lowest reported for fleas in other studies. This suggested that the pressure of parasitism of X. ramesis on G. dasyurus in terms of blood consumed was relatively low. Both our hypotheses were confirmed. Average daily metabolic rate of the parasitized gerbils (7.75 kJ g−0.54d−1) was 16% higher than that of non-parasitized gerbils (6.69 kJ g−0.54d−1). In addition, at zero metabolizable energy intake, the parasitized gerbils lost body mass at a faster rate than the non-parasitized gerbils (4.34 vs 3.95% body mass d−1). The efficiency of utilization of energy in the parasitized and non-parasitized gerbils was similar.

We examined the relationship between intrinsic and extrinsic variables and variation in size at birth and rates of postnatal growth in the big brown bat Eptesicus fuscus at maternity roosts in central Massachusetts and southern New Hampshire. Body mass and length of forearm at birth were lowest when precipitation in the month preceding births was relatively high. In addition, body mass at birth was significantly lower when ambient temperatures during late pregnancy were relatively low. Pups born to middle age mothers were heavier than pups born to young or old mothers. When evaluated using mark–recapture data (longitudinal method), postnatal growth in length of forearm and body mass was greater for pups born to middle age and older mothers and change in body mass was greater for female pups than for male pups. When growth data were evaluated using the trajectory method, the rate of growth for length of forearm was greatest when ambient temperature was highest. Age prediction equations were improved when maternal age was incorporated into predictive equations. We recommend considering both intrinsic and extrinsic variables in studies where maternal effort is evaluated and age prediction equations are used for estimating postnatal growth rates in free-ranging bats.

Cranial variability was studied in 307 Eastern hedgehogs Erinaceus concolor Martin, 1838 from central and south-eastern Europe, the Near East, Middle East, and the Caucasus. The maxillary bone always contacted the nasal bone in European samples, forming a naso-maxillary suture which was mainly long (>2 mm). In contrast, the suture was usually short (<1–2 mm) in hedgehogs from the Near East and Middle East, and sometimes the maxillary failed to reach the nasal bone. In the latter case, the premaxillary formed a suture with the frontal bone (length = 2.5 mm in extreme cases). Two morphotypes could be distinguished on this basis: the roumanicus morphotype (with a long suture) and the concolor morphotype (with the naso-maxillary suture short or absent). Discriminant function analysis of nine geographic samples, and based on 14 linear log-transformed skull measurements, revealed two clusters: one included four European samples of the roumanicus morphotype and the other contained three Asiatic samples of the concolor morphotype. Specimens of the roumanicus morphotype from Asia were classified as having either the concolor or roumanicus morphotype; however, on average their skull morphology suggested closer affinities with the former.

Seven Euplotes spp. were investigated using amplified ribosomal DNA restriction analysis (RFLP, riboprinting). This involved the use of the polymerase chain reaction (PCR) to amplify a segment of the ciliate genome, followed by restriction digestion to yield restriction fragment length polymorphisms among the seven euplotids. Distinctly different restriction digestion haplotypes and similarity indices among the seven species (0.15–0.78) were obtained, which were used to separate the seven species and construct a distance tree among them. Seven species were separated into three clusters: i.e. E. rariseta, E. eurystomus–E. woodruffi–E. octocarinatus–E. charon and E. minuta–E. vannus. The present investigation demonstrates that RFLP riboprinting is a useful technique for species separation. Some limitations of this method for inferring the relationships above species level are discussed.

Limnognathia maerski, class Micrognathozoa, so far known only from Arctic Greenland, is reported from the subantarctic Crozet Islands. Fine morphology of the trophi is redescribed using scanning electron microscopy. Results show that the trophi are composed of the same functional units, i.e. incus, paired mallei and epipharynx, as found in Rotifera Monogononta. The zoogeography of the species is briefly discussed.

The seasonal and spatial pattern of diet composition of a population of wild rabbits Oryctolagus cuniculus L. occupying a southern Portuguese montado was estimated using the n-alkane technique. The diet was analysed in terms of components that are relevant to habitat management. The dietary categories considered were gum cistus leaves and flowers, cork oak and holm oak seedlings and acorns, cereals, olive tree regrowth and grass-forb species. The objectives were to assess the changes in diet across seasons in relation to the reproductive cycle of the rabbits, and to relate these changes to herbaceous biomass availability and to habitat structure, in terms of density of scrub cover and accessibility to arable crops. The results demonstrated that the diet was dominated by grass-forbs, and cereals when they were available. Browse was an important component of the diet and became more important in a year of low herbaceous biomass availability and in areas dominated by dense scrub. A similar phenomenon was observed in relation to consumption of acorns in winter. Seasonal and spatial variation in diet composition suggested a strategy aimed at maintaining a high quality diet. This was supported by the observed high dry matter digestibility of the diet during most of the year. The relevance of growing arable crops and providing fodder, as a means of increasing the carrying capacity of montados for rabbits and protecting the natural regeneration of trees, is discussed.

The cross-sectional geometric properties of the crocodylian humerus were examined in order to assess the effects of differential locomotor behaviour and habitat use on osteological properties. Several biomechanical properties of the humerus were calculated, including resistance to compression and tension, bending and torsion resistance. The biomechanical properties of the crocodylian humerus reflect little variation attributable to locomotor behaviour or natural habitat use (terrestrial vs aquatic habitat). However, the biomechanical properties of captive individuals differed from those of wild conspecifics. The results of this research suggest that crocodylian humeri maintain sufficient resistance to all loading conditions throughout life with little remodelling, though both resorption and remodelling of bone are known to occur. Consequently, crocodylian humeri do not respond to stresses incurred during life as predicted by Wolff's Law.