Helicopter Surveys Research Articles

Monitoring the abundance of mouflon in South France

Monitoring change in the population size of mouflon (Ovis gmelini musimon × Ovis sp.) in rugged areas is an important yet difficult task for wildlife ecologists. To assess population change of mouflon inhabiting the Caroux-Espinouse massif, France, we compared a pedestrian and helicopter survey, using counts of animals as indices of abundance. Environmental factors such as date of survey and temperature affected the detection of mouflons from the ground and the air. Both indices were sensitive to observed changes in population size. A decrease in the pedestrian index was recorded in 1994, the year following an epizootic of keratoconjunctivitis, which markedly reduced the survival rate of mouflon. Variations in pedestrian index accounted for variations in harvests when excluding epizootic events. Both surveys detected a decrease in population size, which accounted for the recent increase of harvest. Helicopter and pedestrian surveys are reliable tools to monitor annually mouflons in mountainous areas. Simulations indicated that helicopter surveys should be preferred by managers because they provide the best trade-off between cost and precision.

Does variable probability of detection compromise the use of indices in aerial surveys of medium-sized mammals?

Although aerial surveys are an effective and commonly used method of monitoring wildlife populations, variable detection probability may result in unreliable indices or biased estimates of absolute abundance. Detection probability can vary between sites, sampling periods, species, group sizes, vegetation types and observers. These variables were examined in helicopter surveys of a suite of medium-sized mammals in a hilly environment in central eastern New South Wales. Maximum-likelihood methods were used to investigate the effects of these variables on detection probability, which was derived using the double-count technique. Significant differences were evident between species in the overall analysis, and group size, vegetation, observer pair and sampling period for various individual species when analysed separately. The implications for monitoring wildlife populations between sites and across time are discussed. This paper emphasises that aerial survey indices may be effective in detecting large differences in population size but can be improved by quantifying detection probabilities for a range of variables.

Mark-resight superpopulation estimation of a wintering elk Cervus elaphus canadensis herd

Abstract We executed four mark-resight helicopter surveys during the winter months January–February for each of the three years 1999–2001 at 7–10 day intervals to estimate population size of a wintering elk Cervus elaphus canadensis herd in northern New Mexico. We counted numbers of radio-collared and uncollared elk on a simple random sample of quadrats from the study area. Because we were unable to survey the entire study area, we adopted a superpopulation approach to estimating population size, in which the total number of collared animals within and proximate to the entire study area was determined from an independent fixed-wing aircraft. The total number of collared animals available on the quadrats surveyed was also determined and facilitated detectability estimation. We executed superpopulation estimation via the joint hypergeometric estimator using the ratio of marked elk counted to the known number extant as an estimate of effective detectability. Superpopulation size estimates were approximately ...

Aerial surveys give new estimates for orangutans in Sabah, Malaysia.

Great apes are threatened with extinction, but precise information about the distribution and size of most populations is currently lacking. We conducted orangutan nest counts in the Malaysian state of Sabah (North Borneo), using a combination of ground and helicopter surveys, and provided a way to estimate the current distribution and size of the populations living throughout the entire state. We show that the number of nests detected during aerial surveys is directly related to the estimated true animal density and that a helicopter is an efficient tool to provide robust estimates of orangutan numbers. Our results reveal that with a total estimated population size of about 11,000 individuals, Sabah is one of the main strongholds for orangutans in North Borneo. More than 60% of orangutans living in the state occur outside protected areas, in production forests that have been through several rounds of logging extraction and are still exploited for timber. The role of exploited forests clearly merits further investigation for orangutan conservation in Sabah.

Determination of ape distribution and population size using ground and aerial surveys: a case study with orang‐utans in lower Kinabatangan, Sabah, Malaysia

AbstractBecause of the difficulties encountered in detecting many large tropical forest‐dwelling species in their natural habitat, precise figures concerning the distribution, number and trends of many populations remain deficient. In tropical forests, ground surveys are generally carried out by counting objects along straight lines. These counts require a strict compliance with the line‐transect methodology before (proper design of the census), during (careful data collection) and after (accurate and correct data processing and analysis) the census itself. In addition, the major source of bias when estimating population size and/or trends comes from the extrapolation of estimates obtained in small sampling areas to the larger, and often incompletely known, distribution of the population. In the Kinabatangan floodplain (Sabah, Malaysia), helicopter surveys were useful in directly assessing the distribution of orang‐utans and were a major advantage in the precise estimation of the size of the orang‐utan population surviving in this region. Our survey showed that about 1100 orang‐utans remain in the multiple‐use forests of the Kinabatangan floodplain. These results provide new evidence on orang‐utan adaptation to habitat disturbance and indicate the potential of the Kinabatangan multiple‐use forests for orang‐utan conservation. Helicopter surveys appear to be a promising alternative to ground survey for precise distribution assessment and for monitoring population trends of apes throughout their entire range in Asia and in some parts of Africa.

THE INFLUENCE OF MOUNTAIN LION PREDATION ON BIGHORN SHEEP TRANSLOCATIONS

Abstract We studied the effects of mountain lion (Puma concolor) predation on 2 translocated populations of bighorn sheep (Ovis canadensis) in New Mexico, USA. During 1993, 32 Rocky Mountain bighorn sheep (O. c. canadensis) were translocated to Wheeler Peak Wilderness Area in northern New Mexico, and during 1992–1993, 31 desert bighorn sheep (O. c. mexicana) were translocated to Sierra Ladron in central New Mexico. We monitored both populations from release through 2000 using fixed-wing aircraft and ground and/or helicopter surveys. We determined cause of mortality for radiomarked individuals (n = 26) and calculated survival rates, cause-specific mortality rates, exponential growth rates, and lamb:ewe ratios. The post-lambing population estimates in 2000 were 180 in Wheeler Peak and 21 in Sierra Ladron. Annual adult survival was higher (P < 0.005) in the Wheeler Peak population (0.955) than in the Sierra Ladron population (0.784). Annual lamb:ewe ratios also were higher (P < 0.001) in the Wheeler Peak pop...

Comparison of helicopter and ground surveys for North American elk Cervus elaphus and mule deer Odocoileus hemionus population composition

Both ground and helicopter surveys are commonly used to collect sex and age composition data for ungulates. Little attention has been paid, however, to whether data collected by each technique are similar. We compared helicopter and ground composition data for both elk Cervus elaphus and mule deer Odocoileus hemionus across a variety of habitats in the state of Washington, USA. We found that ground and helicopter counts differed (P's &lt; 0.002) consistently in male age structure estimates for elk, and that the two survey methods differed in estimates of adult sex ratios for mule deer (P = 0.023). Counts from helicopters provided larger sample sizes, tended to be more consistent annually in their results, and were corroborated by other demographic studies of the test populations. We conclude that helicopter and ground surveys differ for male age structure and perhaps male:female ratios, but are similar for young:female ratios. Managers should maintain a standardized technique using the same survey vehicle for trend analysis of composition data.

Breeding activity, nest site selection and nest spacing of Wedge-tailed Eagles (Aquila audax) in western New South Wales

Eighty active and 59 inactive Wedge-tailed Eagle (Aquila audax) nests were located by opportunistic helicopter surveys, during the 1995–99 breeding seasons. The mean distance to nearest neighbour was used to estimate nesting densities, which were in the order of 1 pair per 3–9 km2. This was considerably higher than that noted in other semi-arid zone studies (∼1 pair per 40–48 km2) and reflected the concentration of nests along two mountain range systems. The lack of suitable nest sites across much of the study area was the probable cause of the clumped distribution of nests. In all, 85 active and inactive nests were visited on the ground during 1995–97 and data collected on nest site characteristics and habitat. Leopardwood (Flindersia maculosa), Beefwood (Grevillea striata) and White Callitris Pine (Callitris glaucophylla) were the most common tree species selected for nest sites; all three of these were commonly associated with the range habitat. Both Leopardwood and Beefwood characteristically display strong forks at approximately two-thirds the height of the tree and all three species are among the tallest tree species within the study area. These results support the general contention that Wedge-tailed Eagles display no preference for particular tree species and build their nests in the commonest tall trees available.

Effect of Adult Sex Ratio on Mule Deer and Elk Productivity in Colorado

Mule deer (Odocoileus hemionus) and elk (Cervus elaphus nelsoni) in Colorado showed a decline in post-harvest young:female ratios during 1975-1995. One hypothesized cause of this decline in productivity is a decline in male:female ratios during the breeding period. We examined Colorado Division of Wildlife (CDOW) deer and elk population composition data obtained from helicopter surveys to see whether sex ratios explained variation in young:female ratios. Data for both deer and elk supported a response of young:100 females ratios to the male:100 females ratios during the previous year. The observed ratios were about 0.25 fawns:100 does per I buck:100 does for deer (95% CI ± 0.14) and 0.28 calves:100 cows per 1 bull:100 cows for elk (95% CI ± 0.12). However, these effects were not adequate to explain the decline in fawn:doe (1.14 fawns:100 does per year) and calf:cow ratios (0.68 calves:100 cows per year) observed during 1975-1995. Differences in the sex ratio:productivity relationship observed between populations suggest that only some areas might show an increase in young:female ratios in response to an increase in male:female ratios, and then only a small increase in young:females was predicted. We did not detect a threshold of male:female ratios for either species that precipitated a drastic decline in productivity. Based on commonly employed population composition surveys, we conclude that increasing post-season sex ratios will have little if any impact on subsequent population productivity.

Sex-Specific Bias in Helicopter Surveys of Elk: Sightability and Dispersion Effects

Sex-ratio data for adult elk (Cervus elaphus) collected from helicopters may be biased if males and females have different sighting probabilities. Sightability models can account for differential sightability if they are sex-specific or if sightability functions are the same for both sexes. I collected sightability data from a sample of radiocollared elk in Washington that included a large proportion of adult males to test 2 hypotheses about sightability: (1) male and female elk had equal sighting probabilities, and (2) the functional relationship between factors affecting sightability and the probability of sighting groups was the same for both sexes. I also tested the hypothesis that the spatial distribution of male and female elk was the same during experimental surveys. Using logistic regression modeling, 1 found that females were >9 times more likely to be seen than males during surveys. A multivariate logistic model containing the variables group size and overstory canopy closure explained sighting probabilities as well as models with more parameters. Sex was related (P < 0.001) to group sightability in univariate analyses, but the effect of sex was nonsignificant (P = 0.77) when group size and canopy closure were present in a multivariate model, indicating sex operated as a confounder but not an effect modifier. The spatial overlap of adult male and female elk in blocks of aerial sampling units was 67% during the sightability trials. The distribution of male and female elk among these blocks was related to sex (P≤0.05) and bivariate relocations from males and females were spatially distinguishable (P<0.001), indicating that males and females were spatially segregated. These results suggest that sightability models need not be sex-specific to reduce bias in sex-ratio data collected from helicopters. However, the spatial distribution of male and female elk during winter is a potential source of bias in helicopter surveys designed to yield accurate sex-ratio data if survey area boundaries are defined by the distribution of high-sightability groups, which are likely to be groups of females.

Aerial treatment of the Australian plague locust, Chortoicetes terminifera (Orthoptera: Acrididae) with Metarhizium anisopliae (Deuteromycotina: Hyphomycetes).

Between October 1999 and April 2000, nearly 4000 ha of nymphal bands and adult swarms of Chortoicetes terminifera (Walker) were aerially treated using a ULV oil formulation of strain FI-985 of Metarhizium anisopliae var. acridum. During the mild weather (maxima 22-30 degrees C) of spring (October), there was little change in nymphal bands during the first week but at all doses between 25-100 g (1-4 x 10(12) conidia) ha(-1), the bands rapidly declined 9-12 days after treatment reaching > 90% mortality by 14 days. Metarhizium persisted for some time as there was 50% mortality of locusts fed vegetation collected from the treated blocks seven days after treatment. Persistence was confirmed by the high mortality of bands that invaded from untreated areas and of nymphs that hatched on the plot five to seven days after treatment, though mortality was then delayed until early in the third week. During summer (January), temperatures were high (maxima 36-42 degrees C), and at all doses between 25 and 125 g (1-5 x 10(12) conidia) ha(-1), there was a rapid decline seven to ten days after treatment. By 12-14 days, there was a > 90% decline in numbers in most blocks which was confirmed by helicopter surveys two weeks after treatment that found very few adults within or near treated areas. Mortality was delayed in the high dose where there were blockages of spray equipment during treatment. The clear demonstration that Metarhizium can suppress small local populations of C. terminifera led to the limited operational use of Metarhizium on an organic farm and in a National Park where nearly 2500 ha of bands and swarms were treated. Continued research is needed to develop a commercially viable product so that Metarhizium can form a significant part of a programme of integrated pest management of locusts in Australia.

Monitoring Crocodylus porosus populations in the Northern Territory of Australia: a retrospective power analysis

In the Northern Territory of Australia, populations of the estuarine crocodile (Crocodylus porosus) have been subject to an annual egg harvest since the early 1980s. Since 1997, adult and juvenile crocodiles have also been harvested in some catchments. Annual surveys of crocodile populations are conducted in order to ensure that the harvest is sustainable. Boat surveys commenced in 1975 and helicopter surveys commenced in 1989. Retrospective power analysis was used to determine whether the sampling program meets the objectives of the Crocodile Management Program for the Northern Territory. Data collected during boat surveys vary in quality between river systems. The analysis of pooled data from 7 river systems with a residual standard deviation of 0.11 indicates that the power of the current spotlight survey method to detect a decline of 10% per annum in around 4 years is about 0.9. In this time the population would decline by around 33% and would fully recover in 8 years following the removal of the factor causing the decline. This allows detection of a decline within one-third, and recovery within two-thirds, of the estimated generation time of the saltwater crocodile and will allow management actions to be implemented before the impacts on populations are serious. The data from helicopter and boat surveys from a 10-year period were compared. Helicopter surveys did not provide useful management information.

Habitat Requirements of White-winged and Surf Scoters in the Mackenzie Delta Region, Northwest Territories

... My thesis work focuses on learning more about the habitat requirements of white-winged and surf scoters in the Mackenzie Delta region. ... This summer, I conducted helicopter surveys of 220 wetlands in 31 randomly selected plots. Half of the plots were in the Delta, and half were in the upland habitat. Each wetland was surveyed twice in June for breeding pairs and twice in early August for broods. Wetlands were then classified as used or not used by pairs and broods of both species. In mid-August, I revisited a subset for used and non-used wetlands to collect water samples and data concerning characteristics of each wetland and its surrounding upland habitat. Initial results indicate that white-winged scoter pairs are more abundant than those of surf scoters in both Delta and upland regions. Pairs of both species occupy upland lakes more frequently than Delta lakes and seem to e more abundant on medium and large wetlands than on small wetlands. Although we observed 394 pairs of white-winged scoters and 68 pairs of surf scoters during the two breeding pair surveys, we observed only 68 white-winged scoter broods and 20 surf scoter broods. The broods were distributed approximately equally between Delta and upland lakes. I am currently compiling and analyzing data to verify these initial impressions and evaluate a habitat selection pattern. I will conduct a second field season next summer to compare predicted scoter distributions (based on results from 2001 data) and observed scoter distributions from independent surveys of new lakes in new plots.

Dynamics of the new south wales yellow-footed rock­wallaby population, in relation to rainfall patterns

Yellow-footed rock-wallabies (Petrogale xanthopus) are listed as endangered in New South Wales (NSW). Annual helicopter surveys have been conducted, during winter, on the NSW population since 1980. Correlation analysis suggested that the exponential rate of increase (r) of the population was positively related to rainfall in the previous calender year. Ivlev's inverted exponential numerical response model was found to adequately represent the relationship between r and rainfall, though the fit was poor (R2 = 0.43). Examination of the fit of the numerical response model and the predictions for the consonants used in the model suggested that the lower end of the function was better approximated than the upper end. The predicted values for the maximum rate of decrease and the level of rainfall at which r would became positive could be intuitively explained given aspects of the wallabies' ecology. However, the estimated maximum rate of increase was far below theoretically predicted values, which suggested that the expected positive correlation between rainfall and recruitment was weak. This suggested that the NSW P. xanthopus population was not primarily regulated by absolute resource availability during the period of the study. Possible intrinsic and extrinsic factors that detrimentally influenced the population are proposed.

Escape responses of hauled out ringed seals ( Phoca hispida ) to aircraft disturbance

Arctic marine mammals may be subject to human-induced disturbance from various air traffic, mostly in connection with exploration and exploitation of non-renewable resources. The escape responses (i.e. leaving the ice) of hauled out ringed seals (Phoca hispida) to a low-flying (150 m) fixed-wing twin-engine aircraft (Partenavia PN68 Observer) during strip censuses in eastern Greenland (June 1984) and to a low-flying (150 m) helicopter (Bell 206 III) during reconnaissance in northwestern Greenland (May 1992) were recorded. Overall, 6.0% of the seals (N tot = 5040) escaped as a reaction to the fixed-wing aircraft. Seals escaped less than about 600 m in front of the aircraft. The overall probability of escaping was 0.21 within a 200-m-wide centre zone, 0.06 on the side of the aircraft (100–300 m from the flight track), and 0.02 between 300 and 500 m from the track. The probability of escaping was found to be influenced by the time of day, relative wind direction and wind chill. Overall, about 49% of all seals (N tot = 227 cases) escaped as a response to the helicopter. Seals entered the water a maximum of about 1250 m in front of the aircraft. At wind chill values below 1100 kcal/m2 h, the probability of escaping was 0.79 in the 200-m-wide centre zone. On the sides the probability of escaping decreased up to about 500 m from the flight track whereafter it remained constant at about 0.30 up to about 1450 m. During the helicopter surveys wind chill was the only environmental factor found to have an additional effect on the probability of escaping. The study indicated that the risk of scaring ringed seals into the water can be substantially reduced if small-type helicopters do not approach them closer than about 1500 m, and small fixed-winged aircraft not closer than about 500 m.

Effects of Egg and Hatchling Harvest on American Alligators in Florida

Harvest of crocodilian eggs and young for captive rearing (ranching) has been used worldwide as an option for producing crocodilian skins and meat from wild stock. The long-term effects of harvesting a certain proportion of early age class, wild American alligators (Alligator mississippiensis) without repatriation is unknown. We removed an estimated 50% of annual production of alligators on Lakes Griffin and Jesup in central Florida over an 11-year period and monitored population levels via night-light counts. Densities of the total alligator population increased (P 0.117), and subadult (122-182 cm TL) alligators increased (P < 0.011) on harvest areas. The density of juveniles on the control area increased (P = 0.006), and the density of subadults showed some evidence of increasing (P = 0.088). No changes were detected in size distributions on the treatment areas. Nest production, as observed from aerial helicopter surveys, increased (P < 0.039) on Lake Woodruff NWR and Lake Jesup and showed some evidence of an increase on Lake Griffin (P = 0.098) during 1983-91. A 50% harvest rate of eggs or hatchlings did not adversely affect recruitment into the subadult or adult size classes.

Development and Evaluation of Sightability Models for Summer Elk Surveys

We developed 2 sightability models from summer helicopter surveys of radiocollared elk (Cervus elaphus) in Grand Teton National Park, Wyoming. Significant variables (P 30% vegetation cover), but this overestimation was ac- counted for by Model B. Thus, we recommend application of the Idaho model during summer surveys where elk are less gregarious (<20 elk) and recommend application of summer Model B to high-density elk popu-

Power and precision of replicated helicopter surveys in mixed bushveld

It is well known that aerial game counts in South Africa are often applied in a non-standardised, unreplicated fashion. They contribute to poor management decisions based on their results as they may be subject to large statistical Type I and II errors. Replicate counts of large herbivores were conducted in a 8 500 ha sample site in the Loskop Dam Nature Reserve in July 1991. These data were used to estimate precision of the counts and estimate statistical power to detect population changes for different combinations of replications and significance levels.

Status of the White-Faced Ibis: Breeding Colony Dynamics of the Great Basin Population, 1985-1997

-The status of the White-faced Ibis (Plegadis chihi) in the Great Basin is of concern because of its small population size and the limited and dynamic nature of its breeding habitat. We analyzed existing annual survey data for the White-faced Ibis breeding in the Great Basin and surrounding area for 1985-1997. Methods varied among colonies and included flight-line counts and fixed-wing aircraft and helicopter surveys. The number of White-faced Ibis breeding pairs in the Great Basin area has nearly tripled since 1985, despite years of severe flooding and drought at major breeding areas. This growth is reflected in both peripheral (i.e., Oregon, California, Idaho) and core (i.e., Nevada and Utah) components of the population. Our data on colony dynamics in Oregon and Nevada illustrate the ability of the highly nomadic White-faced Ibis to compensate for poor conditions at traditional colony sites by moving among colonies and rapidly colonizing newly available wetlands. We suggest that the White-faced Ibis would benefit from a landscape mosaic of well-distributed peripheral wetlands and persistent colony sites. The nomadic nature of the White-faced Ibis and the dynamic nature of their breeding habitat necessitates that wetland management decisions and population monitoring be conducted in a regional context. Received 30 March 1998; accepted 22July 1993.

Effect of Undercounting and Model Selection on a Sightability-Adjustment Estimator for Elk

Aerial surveys of wildlife populations must correct for failure to observe all animals to obtain unbiased population estimates. We captured and radiocollared elk (Cervus elaphus) in northcentral Pennsylvania to develop a linear-logistic model of characteristics of elk groups associated with visibility bias during helicopter surveys. We used this sightability model in a Horvitz-Thompson sightability-adjustment population estimator. The number of elk in a group was positively correlated (P < 0.001), and the percent canopy cover was negatively correlated (P = 0.002) with the probability of observing a group of elk. Observations of elk groups of known size indicated that helicopter crews undercounted elk group sizes, and percentage of elk missed increased as percent canopy cover increased. Probably because of this undercounting, 3 of 6 population estimates from the sightability-adjustment estimator were less than the number of elk known to be alive on the study area. Simulations of elk surveys using our empirical data indicated that our population estimates may have been negatively biased by 20%, because of undercounting. The assumption of complete enumeration of sighted groups of animals should be verified when using this estimator. When all assumptions of the estimator were met during computer simulations, confidence intervals calculated under the assumption of asymptotic normality and log-normality did not provide nominal coverage. We found that a sightability model using only group size as an independent variable, even when the true sightability model also included percent canopy cover, provided population estimates with little negative bias (<1%), shorter confidence intervals, and the lowest mean square error (MSE). Further research is needed on selection of sightability models, and we recommend using a bootstrap technique to calculate confidence intervals. We believe the sightability-adjustment estimator is unsuitable for estimating population size for small populations (≤1,000 animals).