Chris R. Pavey

Population dynamics and prey selection of native and introduced predators during a rodent outbreak in arid Australia

Abstract We examined population dynamics and trophic ecology of a predator–prey system in the Simpson Desert, Australia, consisting of an assemblage of small mammals (body mass < 100 g) and 4 species of predators: the endemic letter-winged kite (Elanus scriptus), a nocturnal-hunting rodent specialist; and 3 introduced mammalian predators (dingo [Canis lupus dingo], European red fox [Vulpes vulpes], and house cat [Felis catus]). This is the 1st comprehensive study of the responses of both the kite and introduced carnivores to a rodent outbreak. The 3.5-year study period included a population outbreak of about 24 months duration involving 3 native rodent species. Mammalian predators and kites exhibited similar population responses. Kites immigrated into the area within 6 months of the outbreak commencing, and remained while rodent abundance was high; however, all birds left the area after rodent populations crashed within a 6-week period. Dingoes and foxes were more abundant than cats and both species increased during the outbreak. All carnivores were resident. The letter-winged kite fed almost entirely on rodents. Rodents were the main prey of the 3 mammalian predators during the outbreak; however, all species had intermediate niche breadths. Dietary overlap between the kite and each carnivore was high during the rodent outbreak. During a nonoutbreak period, predation on rodents by the red fox remained high, whereas that by the dingo declined. We estimated the number of average-sized rodents (body mass 32.65 g) eaten daily by a nonreproducing individual to range from 1 (letter-winged kite) to 6 (red fox). We also estimated that the 3 mammalian predators (combined) captured 11 times as many rodents per day as letter-winged kites. There is considerable potential for food-based competition between the kite and introduced mammalian predators, particularly the red fox and house cat, in arid Australia.

A comparison of three survey methods for collecting bat echolocation calls and species-accumulation rates from nightly Anabat recordings

Bat surveys are frequently undertaken using ultrasonic detectors to determine the species present in an area on the basis of the identity of echolocation calls. We compared three techniques for using the Anabat II detector: the detector pointed along tracks (flyways) versus the detector pointed across tracks (non-flyways); recording output to audio cassette (analogue) versus direct recording to computer (digital); and active hand-held recording versus static automatic recording. In addition, we derived a species-accumulation curve from all-night Anabat recordings in the wet–dry tropics of the Northern Territory. We found no significant difference between flyway and non-flyway recordings; significantly more calls were identified from digital recordings; and significantly more species were detected using hand-held than static recordings. Species-accumulation analysis suggests that the minimum time required to achieve a satisfactory (80%) inventory of bat species at a site is during the three-hour period immediately after sunset. We use our findings to make recommendations for the design of bat surveys using the Anabat II detector.

Thermal Biology, Torpor, and Activity in Free‐Living Mulgaras in Arid Zone Australia during the Winter Reproductive Season

Little is known about the energy conservation strategies of free‐ranging marsupials living in resource‐poor Australian deserts. We studied activity patterns and torpor of free‐living mulgaras (Dasycercus blythi) in arid central Australia during the winter of 2006. Mulgaras are small (∼75 g), nocturnal, insectivorous marsupials, with a patchy distribution in hummock grasslands. Mulgaras (six males, three females) were implanted intraperitoneally with temperature‐sensitive transmitters and monitored for 6–55 d. Temperature profiles for different microhabitats and the thermal properties of soil and a number of burrows were also measured. Air temperature ranged from −3°C at night to 30°C during the day. Although burrows buffered temperature extremes, the thermal diffusivity of the sandy soil was high, and many burrows were shallow. Hence, soil and burrow temperatures averaged about 15°C. The activity of mulgaras was often restricted to a few hours after sunset, before they retired into their burrows. Mulgaras employed torpor frequently, often entering torpor during the night and arousing around midday, with arousals occurring later on cooler days. Shallow burrows allowed cooling below mean Tsoil. Consequently, body temperatures as low as 10.8°C were observed. The longest torpor bout was 20.8 h. Torpor patterns changed seasonally and differed between males and females. From June to August, females entered torpor almost daily despite mating and gestation, but from the end of the gestation period onward, they remained normothermic. In contrast, males showed only shallow and short torpor during the mating season, but from mid‐July, a transition to more frequent and deeper torpor resembling that of females was observed. Apparently, in both sexes, the reproductive effort entails energetic costs, but torpor, as an energy‐saving mechanism, and reproduction are not exclusive in mulgaras. In a resource‐poor environment during the least productive part of the year, frequent torpor seems to provide the means to compensate for the increased energetic costs associated with reproduction.

Bat predation on eared moths: a test of the allotonic frequency hypothesis

Many species of moths (Lepidoptera) possess ears which enable them to hear the echolocation calls of bats and avoid predation. The range of best hearing of eared moths is to frequencies usually between 20 and 50 kHz; therefore, bats with calls above or below these frequencies are predicted to capture eared moths more frequently than other bats. This prediction is the basis of the allotonic frequency hypothesis. We conducted a field test of the hypothesis using three species of flutter-detecting bats which capture flying insects. The species were diadem leafnosed bat Hipposideros diadema (call frequency 55-58 kHz), eastern horseshoe bat Rhinolophus megaphyllus (67-71 kHz) and dusky leafnosed bat H. ater (160-164 kHz). Eared moths represented only 7.2% of individuals among prey remains of H. diadema. Moths dominated the diet of both R. megaphyllus and H. ater, being present in almost all faeces and representing the vast majority of prey remains. However, R. megaphyllus captured predominantly non-eared moths (Anthelidae, Lasiocampidae, Hepialidae) or Gelechioid moths, a superfamily which has not been tested for hearing. By contrast, H. ater fed mostly on eared moths, predominantly members of the family Noctuidae. Eared moths made up 91.7% and 82.5% of all moths captured by H. ater at two sites. The data show that the incorporation of eared moths in the diet was much higher in the bat species, H. ater, with a call frequency well above the range of best hearing of moths. This result supports the allotonic frequency hypothesis. Our study indicates that flutter-detecting bats could have imposed selective pressures on moths during the evolution of moth hearing.

Temporal Patterns of Bats in the Top End of the Northern Territory, Australia

Abstract Temporal activity patterns of microchiropteran bats were assessed at 4 scales (hourly, nightly, monthly, and yearly) in the Top End of the Northern Territory, Australia, in relation to biotic (insect availability) and abiotic features in the environment. At the hourly scale we found activity declined throughout the night and was most closely associated with temperature. At the nightly scale we found associations between bat activity, moonlight, and temperature as well as a complex association with both moon phase and time of night. At the monthly scale we found bat activity increased dramatically in October and provide evidence that this was triggered by a combination of changing climatic factors that occur at this time of year in the Southern Hemisphere tropics. At the yearly scale, no overall difference was found in bat activity between years (n = 4) and no associations were found with climatic variables. At all temporal scales we found no significant associations or differences in species richness and only weak or no associations with insect availability. There also was a high degree of variation in bat activity across all temporal scales that have significant implications for surveying and monitoring microbats.

Population dynamics and spatial ecology of a declining desert rodent, Pseudomys australis: the importance of refuges for persistence

Abstract Desert rodents exhibit irruptive (boom–bust) population dynamics in response to pulses of primary productivity. Such unpredictable population dynamics are a challenge for monitoring population trends and managing populations, particularly for species in decline. We studied the population dynamics and occurrence of populations of the vulnerable plains mouse, Pseudomys australis (42-g body mass), during the low (bust) phase of the cycle in the Simpson Desert, Australia, to examine the use of refuges by the species and the predation pressure experienced from native and introduced predators. Specifically we investigated landscape-scale occurrence; body mass, reproduction, and population size; and presence of native and introduced predators. Our results demonstrate that P. australis contracted to discrete areas of the landscape (refuges) during the low phase and that these areas occupied a small proportion (∼17%) of the range occupied during population peaks. Animals in refuge populations had comparable body mass, occurred at similar densities to populations during the boom phase, and continued to reproduce during dry conditions. Such refuges represented a significant concentration of biomass to predators in a resource-poor environment. Native predators were rare during the low phase, suggesting that refuges naturally experienced low predation levels. Two introduced predators, feral house cats and red foxes, persisted during the low phase and exploited refuge populations of P. australis, thus representing a significant threat to population persistence. We advocate a novel approach to management of rodents in arid systems that involves identifying the discrete parts of the landscape that function as drought refuges and then focusing threat management there. The relatively small size of these refuges increases the likelihood of cost-effective management.

Vertebrate diet decreases winter torpor use in a desert marsupial

One of the energetic benefits of daily torpor over prolonged hibernation is that it enables animals to regularly forage and, therefore, replenish food reserves between bouts of torpor. However, little is known about the diet of predators undergoing torpor or whether differences in prey composition among individuals influence torpor characteristics. Here, we test the hypothesis that prey composition affects winter torpor use and patterns of a population of carnivorous marsupial, the brush-tailed mulgara (Dasycercus blythi), in the Great Sandy Desert, Australia. Mulgaras in the study population captured a wide range of prey including vertebrates (mammals, reptiles, birds), seven insect orders, spiders and centipedes. The proportion of vertebrates in the diet was negatively correlated with both frequency of torpor use and maximum bout duration. This variation in torpor use with diet can be explained by the higher energetic content of vertebrates as well as their larger size. Even assuming uniform intake of prey biomass among individuals, those that subsisted on an invertebrate-dominated diet during winter apparently suffered energetic shortages as a result of the scarcity of invertebrate taxa with high energy content (such as insect larvae). Our study is the first to demonstrate a link between diet composition and daily torpor use in a free-ranging mammal.

Prey availability affects daily torpor by free-ranging Australian owlet-nightjars (Aegotheles cristatus)

Food availability, ambient temperatures (Ta), and prevailing weather conditions have long been presumed to influence torpor use. To a large extent, this is based on measurements in the laboratory of animals placed on restricted diets and kept at low Ta. Information on the determinants of torpor employment in the field is limited. We assessed winter torpor by insectivorous, free-ranging Australian owlet-nightjars (Aegotheles cristatus; 22 birds, 834 bird-days over six winters). Birds in three habitats were investigated to test whether torpor use is affected by annual Ta, rainfall, and arthropod abundance. Owlet-nightjars entered daily torpor regularly at all sites. Torpor frequency, depth and bout duration were greatest during two periods with lower arthropod abundance, providing rare evidence of the link between food availability and torpor patterns of wild birds. Temporal organization of torpor was similar among sites, and nocturnal torpor was more frequent than previously reported. Our findings quantitatively demonstrate that reduced food resources affect torpor usage independently from Ta, and support the view that food availability is a primary ecological determinant of torpor use in the wild.

Home range and spatial organisation of rock-dwelling carnivorous marsupial, Pseudantechinus macdonnellensis

We studied home-range size, range length and spatial organisation of fat-tailed false antechinus, Pseudantechinus macdonnellensis, at Ormiston Creek, central Australia. Animals were tracked using transmitters implanted into the body cavity. Mean home-range size was 0.76 ha based on the minimum convex polygon (MCP) method and 1.14 ha based on the fixed kernel method (95% contour). Mean size of core areas of the home range was 0.07 ha based on the 50% kernel contour. Mean maximum range length was 148.83 m. Males occupied larger home-range areas than females (MCP: 0.98 v. 0.31 ha, 95% fixed kernel: 1.50 v. 0.43 ha) and also had greater maximum range lengths (180 v. 86 m). Home-range areas showed little overlap within the sexes; however, ranges of males overlapped those of females by an average of 37.95%. By comparison with data from a previous mark-recapture study at the same site, radio-tracking produced home-range estimates (MCP) that were greater by a factor of 24.5 for males and 15.5 for females, whereas maximum range lengths were lower for females, but similar for males. The results of this study support the proposition that the rock-dwelling P. macdonnellensis has a more stable home range and undergoes fewer long-range movements than similar-sized arid-zone dasyurids that occupy open environments. These differences likely result from the stability in resources provided by rocky habitats, specifically year-round availability of insects, availability of plentiful shelter sites that are very effective thermal buffers in both summer and winter, and a diversity of accessible microclimates. W R Spa ti Psechic i C. R. P

Basking and diurnal foraging in the dasyurid marsupial Pseudantechinus macdonnellensis

Several mammal species bask to passively rewarm during arousal from torpor, a strategy that can decrease energetic costs. Nothing is known about basking behaviour in these species or the trade-offs between energetic benefits of basking and potential costs associated with changes in activity patterns and increased predation risk. We assessed basking during winter in Pseudantechinus macdonnellensis, an Australian arid-zone marsupial that belongs to a family (Dasyuridae) that is typically nocturnal. Animals were implanted with temperature-sensitive transmitters to assess body temperatures and to assist in visually locating animals active during the day. Tagged animals regularly exhibited diurnal foraging. Foraging bouts occurred throughout the day; however, most bouts were observed within 3h of sunset. By comparison, basking occurred much more frequently in the morning. Basking and a shift towards diurnal foraging in winter is associated with a decrease in richness and abundance of predators. P. macdonnellensis appears to compensate for the occurrence of torpor during the active phase (i.e. night) in winter by changing activity patterns such that foraging commences during what is usually the rest phase. These activity patterns are not expected to occur during the remainder of the year.