Ventilation of the branchial chambers in the amphibious West African freshwater crab,Sudanonautes (Convexonautes) aubryi monodi (Balss, 1929) (Brachyura,Potamonautidae)

The anatomy of the respiratory system of the savanna-zone African freshwater crab, Sudanonautes (Convexonautes) aubryi monodi [Balss, 1929], has been examined and has been found to be adapted for both aerial and aquatic gas exchange. The activities of the scaphognathites and the directions of flow of the ventilatory stream have been recorded in stressed, active and resting specimens during their exposure to a wide range of conditions from deep water to dry land.Ventilation of the branchial chambers during aquatic gas exchange in Sudanonautes kept in deep water is shown to consist of a rapid, predominantly forward water flow similar to that of fully-aquatic species. Ventilation of the branchial chambers during aerial gas exchange in Sudanonautes on land is shown to consist of a relatively slow forward air flow. This flow is continuous in post-operative crabs, pulsatile in active crabs and completely immobile in resting crabs.A second method of ventilation of the branchial chambers during aerial gas exchange is shown to consist of a pulsatile reversed air flow. This occurs (1) when Sudanonautes is kept in very shallow water and active or stressed; (2) when it has recently moved on to land; and (3) when it is completely immersed and exhibiting aerial gas exchange under water. The unusual phenomenon of aerial gas exchange under water is reported here for the first time in any species of crab.Bimodal ventilation of the branchial chambers occurs in stressed or active crabs partly immersed in shallow water. This consists of an alternation between forward water flow and reversed air flow.The morphology of the branchial chambers in Sudanonautes, and observational data on the patterns of ventilation of the branchial chambers, are discussed in relation to those described for other air-breathing decapod crustaceans.     

PHOTOMOVEMENT RESPONSES OF PORPHYRIDIUM PURPUREUM1

The influence of light quality on positive phototopotaxis by the gliding, unicellular red alga Porphyridium purpureum was obtained using interference filters. Cells exposed to 3 × 10^?7 mol · m²· s^?1 of various wavelengths for 72 h showed maximum topotaxis at 420 and 440 nm. The lower threshold for positive, movement was approximately 5 × 10^?8 mol · m^?2· s^?1. Random movement occurred at nonactinic wavelengths, and no movement occurred in the dark. Cell motility appeared to be unaffected by light polarity, suggesting that the photoreceptor(s) for topotaxis and photokinesis are randomly oriented.     

AERIAL CENSUS OF PACIFIC WALRUSES IN THE CHUKCHI SEA, 1985

The U.S. Fish and Wildlife Service conducted a survey of the walruses in the pack ice of the Chukchi Sea between 16 September and 2 October 1985, as part of a joint effort with the Soviet Union to estimate the size of the Pacific walrus population. American observers conducted censuses from two aircraft along randomly selected north–south lines over the pack ice. The observers counted walruses within a constant viewing angle that corresponded to a total strip width of 1.38 km at an altitude of 152 m.
In nine days of flying, 15,312 walruses were observed, of which 10,140 were on 5,764 km² of census strips. Few walruses were observed east of 161°W longitude or west of 170°W longitude, hence the census effort was stratified. Walrus concentrations between 161° and 170° shifted slightly westward during the 2-wk duration of the censuses. The differences among days in observed walrus density were due to changes in the numbers of walruses on the ice within 37 km of the ice edge. The number of observable walruses in pack ice of the eastern Chukchi Sea was estimated to be 62,177 (SD = 19,480), based on censuses conducted on 29 and 30 September and 1 October. At that time there were also at least 15,238 in Bristol Bay, Bering Sea. The Soviets counted 39,572 on the shores of the western Chukchi and Bering seas and estimated 115,531 in pack ice of the western Chukchi Sea. Summing U.S. and Soviet estimates, the total population of Pacific walruses in 1985 was 232,518. This number was comparable with earlier estimates from censuses conducted jointly by the U.S. and the Soviets. However, information on fraction hauled out, segregation, and movements is needed for more precise estimates.     

From small Maria to massive Campbell: Forty years of rat eradications from New Zealand islands

Abstract

Over the last four decades the eradication of rats from islands around New Zealand has moved from accidental eradication following the exploratory use of baits for rat control to carefully planned complex eradications of rats and cats (Felis catus) on large islands. Introduced rodents have now been eradicated from more than 90 islands. Of these successful campaigns, those on Breaksea Island, the Mercury Islands, Kapiti Island, and Tuhua Island are used here as case studies because they represent milestones for techniques used or results achieved. Successful methods used on islands range from bait stations and silos serviced on foot to aerial spread by helicopters using satellite navigation systems. The development of these methods has benefited from adaptive management. By applying lessons learned from previous operations the size, complexity, and cost effectiveness of the campaigns has gradually increased. The islands now permanently cleared of introduced rodents are being used for restoration of island‐seabird systems and recovery of threatened species such as large flightless invertebrates, lizards, tuatara, forest birds, and some species of plants. The most ambitious campaigns have been on remote subantarctic Campbell Island (11 300 ha) and warm temperate Raoul Island (2938 ha), aimed to provide long‐term benefits for endemic plant and animal species including land and seabirds. Other islands that could benefit from rat removal are close inshore and within the natural dispersal range of rats and stoats (Mustela erminea). Priorities for future development therefore include more effective methods for detecting rodent invasions, especially ship rats (Rattus rattus) and mice (Mus musculus), broader community involvement in invasion prevention, and improved understanding of reinvasion risk management.     

New technologies in the mix: Assessing N‐mixture models for abundance estimation using automated detection data from drone surveys

1. Reliable estimates of abundance are critical in effectively managing threatened species, but the feasibility of integrating data from wildlife surveys completed using advanced technologies such as remotely piloted aircraft systems (RPAS) and machine learning into abundance estimation methods such as N‐mixture modeling is largely unknown due to the unique sources of detection errors associated with these technologies.
2. We evaluated two modeling approaches for estimating the abundance of koalas detected automatically in RPAS imagery: (a) a generalized N‐mixture model and (b) a modified Horvitz–Thompson (H‐T) estimator method combining generalized linear models and generalized additive models for overall probability of detection, false detection, and duplicate detection. The final estimates from each model were compared to the true number of koalas present as determined by telemetry‐assisted ground surveys.
3. The modified H‐T estimator approach performed best, with the true count of koalas captured within the 95% confidence intervals around the abundance estimates in all 4 surveys in the testing dataset (n = 138 detected objects), a particularly strong result given the difficulty in attaining accuracy found with previous methods.
4. The results suggested that N‐mixture models in their current form may not be the most appropriate approach to estimating the abundance of wildlife detected in RPAS surveys with automated detection, and accurate estimates could be made with approaches that account for spurious detections.

     

Spatial and temporal factors influencing sightability of elk

Few tracking studies consider seasonal changes in ability to re-sight wildlife, despite potential for biases in sightability to mislead our interpretation of models of movement and abundance. We developed seasonal sightability models based on visual observations of radio-collared elk (Cervus elaphus) in Manitoba, Canada, through 6 seasons. We located 377 elk 8,862 times using aerial telemetry from 2002 to 2009. We tested the hypothesis that sites where we were able to visually observe radio-collared elk during aerial telemetry differed from sites where collared elk were known to be present but could not be sighted. Relationships varied with season and elk sightability was influenced by forest type, habitat openness, distance to edge, and time of day. Our results confirm that observers have the highest probability of detecting elk in early and late winter. However, factors such as day length, which increases by 64% during this period, suggest that fewer impediments to detection exist in late winter. Our findings reinforce the need to account for seasonal as well as spatial changes in habitat-specific sightability models. © 2011 The Wildlife Society.     

Aerial flow of barley yellow dwarf viruses and of their vectors in western France

During the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights. Results from transmission tests showed that: (i) the two main BYDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector as R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infections.     

Comparative efficacy of two controlled-release gypsy moth mating disruption formulations

The effects of aerial applications of the gypsy moth sex pheromone, disparlure, on mating disruption and suppression of growth of populations of the gypsy moth, Lymantria dispar (L.), were investigated. Two formulations of disparlure, plastic laminate flakes applied in a single application and polymethacrylate beads applied in two applications, were compared in two separate tests conducted in 1993 and 1994. The beads were applied in two applications spaced 2 weeks apart because preliminary tests had indicated that they released pheromone too rapidly to maintain adequate emission rates throughout the period of male flight. In 1993, the flakes were applied at a rate of 50 g a.i./ha, and the beads were applied at a rate of 15 g a.i./ha for each application. In 1994, the flakes were applied at a rate of 75 g a.i./ha and the beads were applied at rates of 32.5 and 42.5 g a.i./ha for the two applications. Beads with larger average particle size were used in 1994 to prolong disparlure release. The treatments applied in 1993 resulted in >97% reduction in mating and >82% suppression of population growth in the following year. Because of a 1995 collapse of gypsy moth populations in the vicinity of the tests, reliable population growth data were not available for the treatments applied in 1994, but significant mating disruption did occur under both treatments. Based on measurements of residual disparlure after field aging, the flakes released 32 and 48% of their disparlure content during the 6 weeks of male moth flight in 1993 and 1994, respectively. The smaller beads used in 1993 released 75% of their disparlure content, and the larger beads used in 1994 released 52% of their disparlure content, during the 6 weeks of male flight. The biological efficacy data suggest that the bead and flake formulations, as applied in these tests, have similar effects on gypsy moth mating disruption and subsequent population growth. Based on the observed release rates from both 1993 and 1994, a single application of the beads would provide emission rates equal to or greater than those provided by the flakes when applied at an equal dose.     

Fine‐scale bird monitoring from light unmanned aircraft systems

Unmanned aircraft systems (UAS) are remote‐controlled devices capable of collecting information from difficult‐to‐access places while minimizing disturbance. Although UAS are increasingly used in many research disciplines, their application to wildlife research remains to be explored in depth. Here, we report on the use of a small UAS to monitor temporal changes in breeding population size in a Black‐headed Gull Chroicocephalus ridibundus colony. This method makes it possible to obtain georeferenced data on nest locations without causing colony disturbance, which would not otherwise be possible via direct ground observations.     

Invasive Snake Activity Before and After Automated Aerial Baiting

Aerially delivered toxic baits have proven effective for landscape-level control of numerous invasive vertebrate populations with major benefits for conservation and ecosystem function, but this technique has not been broadly adapted for control of invasive reptiles. Nonnative brown treesnakes (Boiga irregularis) on the Pacific island of Guam have caused severe ecological and economic damage and pose an invasion risk on other islands, making them a high-profile candidate for application of aerial baiting methods. Although terrestrial applications of traps, toxicants, and hand-removal are standard brown treesnake management practices, these methods are not cost-effective for control in the island's large tracts of remote, rugged forest. In 2016, the first major in situ evaluation of a helicopter-borne automated aerial bait delivery system applied snake-targeted toxic baits at an effective rate of approximately 120 baits/ha over a 110-ha forested test plot on Guam. We evaluated the extent and duration of the suppressive effect of this toxic bait application on brown treesnakes by measuring nontoxic bait take rates as a proxy index of relative snake abundance before and after toxic bait application in a treatment plot and surrounding reference area. We placed 4,420 nontoxic baits in random transects at georeferenced locations, from 1 month before until nearly 12 months after toxic bait application, allowing temporal analysis of the suppressive effect and spatial analysis of treatment plot reinvasion. Over the first 30 days after toxic bait application, average nontoxic bait take rate in the treatment plot was 41.2% lower than the pre-application rate, and there was no immediate decrease in bait take in the reference area. Reduced snake activity was still evident nearly 12 months after bait application. Roads forming a portion of the treatment boundary appeared to slow snake movement between treated area and surrounding untreated area. Trail cameras monitoring a subset of bait tubes showed that 97.5% of baits removed were taken by snakes rather than nontarget species. We indexed rodent abundance in the treatment plot and reference area, and found no indication of a rodent population increase following toxic bait application. Our results show that automated aerial bait applications can suppress brown treesnake abundance over a large area and that reinvasion from surrounding untreated habitat occurs over several months. We anticipate that repeated bait applications could achieve and maintain greatly reduced brown treesnake abundance on a landscape scale, potentially improving biosecurity and enabling experimental reintroduction of native birds extirpated by brown treesnake predation. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.