Journal of Zoology

Bradley, B. J.; Doran‐Sheehy, D. M.; Vigilant, L.

doi: 10.1111/j.1469-7998.2008.00431.xpmid: N/A

Western gorillas Gorilla gorilla have been exceedingly difficult to habituate to the presence of human observers. Nevertheless, researchers have amassed a wealth of information on population densities and group structure for this ape species by locating and counting the sleeping nests of wild individuals. Such nest‐count studies have suggested that western gorilla groups often have multiple silverbacks and these multimale groups occasionally divide into smaller subgroups. However, observational data from forest clearing sites and from a few recently habituated western gorilla groups show no evidence of multimale family groups or of subgrouping. This discrepancy underscores a long‐standing question in ape research: How accurately do nesting sites reflect true group compositions? We evaluated these indirect measures of group composition by using DNA from faeces and hair to genetically identify individual gorillas at nesting sites. Samples were collected from unhabituated wild western gorillas ranging near Mondika Research Center in the Central African Republic and Republic of Congo. DNA extracted from these samples was genotyped at up to 10 microsatellite loci and one X–Y homologous locus for sex identification. Individuals were then identified at nesting sites by their unique multilocus genotypes, thus providing a ‘molecular census’ of individual gorillas. Results confirm that western gorillas often build more than one nest at a nesting site and, thus, nest counts can be highly inaccurate indicators of group size and composition. Indeed, we found that nest counts can overestimate group size by as much as 40%, indicating that true gorilla population numbers are probably lower than those reported from census surveys. This study demonstrates how genetic analysis can be a valuable tool for studying and conserving elusive, endangered animals.

Laundré, J. W.

doi: 10.1111/j.1469-7998.2008.00443.xpmid: N/A

Estimates of predation rates by large predators can provide valuable information on their potential impact on their ungulate prey populations. This is especially the case for pumas Puma concolor and its main prey, mule deer Odocoileus hemionus. However, only limited information on predation rates of pumas exist where mule deer are the only ungulate prey available. I used VHF telemetry data collected over 24‐h monitoring sessions and once daily over consecutive days to derive two independent estimates of puma predation rates on mule deer where they were the only large prey available. For the 24‐h data, I had 48 time blocks on female pumas with kittens, 43 blocks on females without kittens and 30 blocks on males. For the daily consecutive data, the average number of consecutive days followed was 51.5±4.2 days. There were data on five female pumas with kittens, five pregnant females and nine females without kittens. Predation rates over an average month of 30 days from the 24‐h monitoring sessions were 2.0 mule deer per puma month for males (15.1 days per kill), 2.1 mule deer per puma month (14.3 days per kill) for females without kittens and 2.5 mule deer per puma month (12.0 days per kill) for pregnant females and females with kittens. For the consecutive daily data, females without kittens had an estimated predation rate of 2.1±0.14 mule deer per puma month (14.9±0.90 days per kill). Pregnant and females with kittens had predation rates of 2.7±0.18 and 2.6±0.21 mule deer per puma month, respectively (11.4±0.72 and 12.0±1.1 days per kill, respectively). Predation rates estimated in this study compared with those estimated by energetic demand for pumas in the study area but were lower than other field derived estimates. These data help increase our understanding of predation impacts of large predators on their prey.

Millon, A.; Arroyo, B. E.; Bretagnolle, V.

doi: 10.1111/j.1469-7998.2008.00447.xpmid: N/A

Food supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life‐history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis.

Kabat, A. P.; Blackburn, T. M.; McKechnie, A. E.; Butler, P. J.

doi: 10.1111/j.1469-7998.2008.00446.xpmid: N/A

The use of allometric scaling to estimate drug doses, regimes, and clearance rates (metabolic dosing) is based on the principle that the amount of drug to be administered is more closely related to daily energy use than to body mass (kg). Thus, by using the allometric estimations of minimal energy consumption (MEC) in kcal day−1 based on the formula MEC=kMbb, where b=3, it is thought to be possible to extrapolate appropriate drug dosage regimens to species for which direct MEC data are unavailable. However, the allometric equations for respiratory variables in birds were developed 30 years ago, and were based on a very small sample size, while the appropriate scaling exponent for the allometry of energy use is a matter of considerable debate. Hence, we revisit the issue of the scaling of therapeutic regimes in birds using the most current expanded database available (resting metabolic rate data for 296 species across 17 bird orders), taking account of the non‐independence of species in this process using a phylogenetically independent approach. We show that the use of caloric values to estimate daily energy consumption introduces significant error into the formula, as there are a number of assumptions that are made when converting rate of oxygen consumption to a caloric value. We also show that there are significant differences in the proportionality or Hainsworth coefficients k across taxa when the data are examined in a phylogenetic context, although the allometric scaling exponent does not vary. We therefore recommend the use of only data based on oxygen consumption values, and not caloric values, and a multi‐order phylogenetic model when calculating the appropriate drug dosage regime.

Gartner, G. E. A.; Greene, H. W.

doi: 10.1111/j.1469-7998.2008.00448.xpmid: N/A

A key component to any adaptive hypothesis is that the adaptive trait in question must confer a performance advantage and, in turn, an increase in fitness, relative to those animals displaying the phylogenetically antecedent condition. Among the most striking purported adaptations in vertebrates are those found in the African snake genus Dasypeltis. These snakes are unique in that they eat bird eggs to the exclusion of all other prey. Detailed functional morphological analysis dating back 50 years has highlighted a suite of morphological features in the head and trunk region hypothesized to assist these animals in eating bird eggs, and yet no comparative performance studies of egg‐eating ability have ever been conducted in this group of snakes. The purpose of this study was twofold: first, we wanted to compare egg‐eating performance in Dasypeltis with a facultative egg eater, the common king snake Lampropeltis getula. Second, we wanted to test the hypothesis that a selective regime exists in Africa conducive to the selection and subsequent fixation of the hypothesized egg‐eating morphological adaptations. Our results show that a strong advantage exists in egg‐eating ability for Dasypeltis. The difference is so large (only large Lampropeltis can eat small eggs) that analysis by analysis of covariance becomes difficult due to problems with collinearity. Our results examining potential selective regimes show that more birds lay eggs of a readily ingestible size in Africa than in a representative region in the United States. Additionally, the largest radiation of African ground‐nesting birds existed in Africa before the colubrid explosion during the Miocene, which gave rise to Dasypeltis, giving further support to previous adaptive hypotheses regarding the unique morphology of these snakes.

Manjerovic, M. B.; Kinahan, A. A.; Waterman, J. M.; Bennett, N. C.; Bateman, P. W.

doi: 10.1111/j.1469-7998.2008.00449.xpmid: N/A

The few studies that have looked at genital allometry in mammals have typically shown a positively allometric relationship with body size and high coefficients of variation. Cryptic female choice, sexual conflict or sperm competition are mechanisms underlying genital evolution and as these are not mutually exclusive, they are often difficult to disentangle. In addition, these mechanisms are affected by both male and female social structure and/or mating strategies and, as such, pre‐ and post‐copulatory behaviours have been shown to alter selection on genitalia. We examined genital traits and allometry in a polygynandrous and social ground squirrel Xerus inauris. We found that male testes are positively allometric and account for 1.5% of their body weight, one of the highest percentages known for sciurids. The penis, at 42.4% of head/body length, was isometric while the female reproductive tract, 22.4% head/body length, demonstrated no such relationship. Based on the allometric relationships of both males and females presented here, in conjunction with high levels of competition for females and lack of male aggression and territoriality, we suggest that sperm competition is the most likely mechanism for the evolution of the extremely large genitalia in this species.

Watanabe, Y.; Wei, Q.; Yang, D.; Chen, X.; Du, H.; Yang, J.; Sato, K.; Naito, Y.; Miyazaki, N.

doi: 10.1111/j.1469-7998.2008.00451.xpmid: N/A

The swimbladder of fishes is readily compressed by hydrostatic pressure with depth, causing changes in buoyancy. While modern fishes can regulate buoyancy by secreting gases from the blood into the swimbladder, primitive fishes, such as sturgeons, lack this secretion mechanism and rely entirely on air gulped at the surface to inflate the swimbladder. Therefore, sturgeons may experience changes in buoyancy that will affect their behavior at different depths. To test this prediction, we attached data loggers to seven free‐ranging Chinese sturgeons Acipenser sinensis in the Yangtze River, China, to monitor their depth utilization, tail‐beating activity, swim speed and body inclination. Two distinct, individual‐specific, behavioral patterns were observed. Four fish swam at shallow depths (7–31 m), at speeds of 0.5–0.6 m s−1, with ascending and descending movements of 1.0–2.4 m in amplitude. They beat their tails continuously, indicating that their buoyancy was close to neutral with their inflated swimbladders. In addition, their occasional visits to the surface suggest that they gulped air to inflate their swimbladders. The other three fish spent most of their time (88–94%) on the river bottom at a depth of 106–122 m with minimum activity. They occasionally swam upwards at speeds of 0.6–0.8 m s−1 with intense tailbeats before gliding back passively to the bottom, in a manner similar to fishes that lack a swimbladder. Their bladders were probably collapsed by hydrostatic pressure, resulting in negative buoyancy. We conclude that Chinese sturgeons behave according to their buoyancy, which varies with depth due to hydrostatic compression of the swimbladder.

Dillon, A.; Kelly, M. J.

doi: 10.1111/j.1469-7998.2008.00452.xpmid: N/A

Because ocelots Leopardus pardalis and other solitary carnivores are elusive and hard to study, little is known about their density and population status. In the past few years, camera trapping and mark–recapture statistics have been used to estimate the density of a number of felids. Although camera trapping is now providing baseline data for managers and conservationists alike, recent doubts have been raised concerning the accuracy of the standard camera trapping procedure. We used radio telemetry to gain new information on ocelot home‐range size and spatial organization in Central America, and compared the radius of our average ocelot home range with the standard camera trapping buffer. We compared the resulting density estimates to assess the current camera trapping methodology's ability to estimate animal density. Five adult ocelots (two male and three female) were tracked to determine an average ocelot home range of 26.09 km2 (95% fixed kernel) and 18.91 km2 (100% minimum convex polygon), with males demonstrating larger ranges than females. All ocelots had larger home ranges in the dry season. Male–male home‐range overlap averaged 9% while female–female overlap averaged 21%. Males shared 56% of their range with a primary female and 16% with a second and third female, while females shared 58% of their home range with a primary male and 3% with a secondary male. Density estimates based on the average home‐range radius (11.24–12.45 ocelots per 100 km2) were less than those determined from standard camera trapping methods (25.88 ocelots per 100 km2), but similar to those determined using twice the camera trapping buffer to estimate density (12.61 ocelots per 100 km2). Our results suggest that a standard camera trapping protocol may overestimate ocelot density. Accurate representation of animal densities and standardization of density estimation techniques are paramount for comparative analyses across sites and are vital for felid conservation.

Clark, N. J.; Gordos, M. A.; Franklin, C. E.

doi: 10.1111/j.1469-7998.2008.00454.xpmid: N/A

Australia has a number of bimodally respiring freshwater turtle species that use aquatic respiration to extend their aerobic dive limit. While species variations in reliance on aquatic respiration are reflected in the diving behaviour and ecology of adults, it is unknown whether these relationships also occur in hatchling and juvenile turtles. This study compared the diving behaviour, aquatic respiration and blood respiratory properties of hatchling and juveniles from five species of Australian freshwater turtles: Rheodytes leukops, Elusor macrurus, Elseya albagula, Elseya latisternum and Emydura signata. Both diving behaviour and physiology differed significantly between species as well as age classes. Dive duration in R. leukops was 17 times longer than the other species, with two hatchlings remaining submerged for the entire 72 h recording period. The long dive duration recorded for R. leukops was supported by a high reliance on aquatic respiration (63–73%) and high blood oxygen affinity (P50=17.24 mmHg). A correlation between dive duration, aquatic respiration and blood respiratory properties was not observed in the remaining turtle species where, despite the longer dive duration of Els. albagula and Elu. macrurus compared with Em. signata and Els. latisternum, there was no difference observed in per cent aquatic respiration or blood oxygen affinity between these species. When compared with adult individuals (data from previous studies), dive duration was positively correlated with body size in Em. signata, Els. albagula and R. leukops, but a negative relationship occurred in Els. latisternum and Elu. macrurus.

Mysterud, A.; Bonenfant, C.; Loe, L. E.; Langvatn, R.; Yoccoz, N. G.; Stenseth, N. C.

doi: 10.1111/j.1469-7998.2008.00453.xpmid: N/A

Tactics for resource‐use involve both using stored reserves (capital breeding) and feeding while reproducing (income breeding). In polygynous ungulates, males often use an income breeding strategy when young and shift to a capital breeding tactic at prime age. Little is known regarding why prime‐aged males stop or largely reduce eating during rut but still remain inactive for as much time as before rut. A detailed exploration of how rumen content correlates with age and date may shed light on the ultimate causes of why some males stop eating. We provide quantitative empirical data on rumen content from red deer Cervus elaphus during the rutting season in Norway. In male red deer, rumen content declined with age, up to around 6 years of age. Above this age, rumen content was low and stable. A time‐of‐year effect on rumen content was best described with a second‐order polynomial term, as rumen fill was lowest during mid‐October when the mass loss of males and the ovulation rate of females both peak. We present two new hypotheses related to why males reduce eating (physical rest and parasite hypotheses). Two related patterns need to be explained and better documented: (1) why are resting times stable before, after and during rut, and (2) why do non‐prime‐aged males eat more between rutting activities?