Aerial Transect Surveys Research Articles

On inferring population trends of mobile waterbirds from aerial transect surveys in variable environments

Monitoring waterbird populations in Australia is challenging for reasons of counting logistics, and because population aggregation and dispersion can shift rapidly in response to large spatio-temporal variations in resource availability. The East Australian Waterbird survey has conducted annual, aerial, systematic counts of waterbirds over eastern Australia for almost 40 years. It was designed to monitor waterbird populations using design-based inference though for many species this form of inference appears inadequate in the face of these challenges. Here we develop a state-space model-based Bayesian approach that, in addition to explicitly incorporating process noise and observation uncertainty, uses random effects and rainfall-derived covariates to model the year-to-year variation in the proportion of the total (super) population that is present on surveyed wetlands, and available to be counted. We use this model-based approach to estimate the superpopulation size of 45 waterbird species annually, and model the rate of population increase as a function of antecedent rainfall. The results confirm the strong positive effect of antecedent rainfall on population growth rates for nearly all species, and illustrate that species respond to rainfall differently in terms of habitat use, which influences whether they are present on surveyed wetlands. For many species, the year-to-year variation in the estimated proportion of the population on surveyed wetlands is very high. The results have implications for making inferences on population trends from these data, with the ability to model the year-to-year sampling variation a key requirement before the rate of population increase can be estimated with any precision. This study illustrates how to progress this approach, and infers that under average rainfall conditions, the general trend is for estimated superpopulation rates of increase to be negative, though for only a few species is this occurring with strong belief.

Lifetime, known‐age moose reproduction in a nutritionally stressed population

ABSTRACTQuantifying long‐term, low reproductive metrics indicative of an ungulate population's low nutritional status can help spur action to manage for moderate densities in contrast to unsustainable, high densities. We previously ranked the moose (Alces alces gigas) population described here as having the lowest nutritional status among 14 moose populations in Alaska, USA, primarily using reproductive indices (1996–2005) from moose with ages estimated by counting cementum annuli. Here, we detailed lifetime reproductive metrics from a subset of known‐age female moose initially radio‐collared at 9–10 months of age (7 cohorts; 1996–2002); we renewed radio‐collars as necessary. We radio‐tracked and circled these moose via aircraft at 24‐ or 48‐hour intervals to detect the presence of newborns during the 1998–2018 calving seasons, with meaningful annual sample sizes during 2000–2014. The number of snow‐free days in the year preceding parturition had a subtle positive effect on parturition probability, but we found no evidence for effects of the preceding February and March immobilization, cohort affiliation, or the preceding winter's snow cover on the probability of a female being parturient. The probability of twinning declined as the calving season progressed. Compared with moose production in populations with improved nutrition, our study population experienced low production primarily as a result of delayed maturation, occasional pauses in reproduction, and low twinning rates. Reproductive senescence occurred at normal advanced ages despite nutritional stress. We recorded a 28% parturition rate among 144 females 3 years of age (min. age of reproduction). Parturition rates were stable from 4 to 13 years of age ( = 77%), declined at 14 years of age, and peaked at 15 years of age. Females first twinned at 5 years of age (5%), and the twinning rate increased with age, peaking at 13 years of age (25%). Overall, 136 radio‐collared females with complete reproductive histories produced a mean of 5.3 calves/lifetime while being monitored a mean of 7.1 years at ages ≥3 years, although variability in individual production was high. Delaying or pausing reproduction increased the parturition rate at 4 and 5 years of age. However, females that delayed first reproduction produced fewer calves/lifetime on average compared with moose that first produced at 3 years of age. Virtually all moose regularly gave birth with occasional 1‐year pauses that acted to enhance production the subsequent year; the incidence of 2 consecutive nonparturient years was 2.8% (24/844). Moose experienced relatively stable, low nutritional status during 2000–2014 based upon low population‐wide twinning rates from annual aerial transect surveys (no telemetry) flown a few days after the median annual calving dates. Detailed understanding of low reproductive metrics encouraged empowered stakeholders to allow liberal harvests of female moose (2.0–4.4% of prehunt moose population numbers) and encouraged land managers to allow wildfires to burn 25% of the study area to improve moose carrying capacity. We helped manage a 31% decline in moose numbers during 2004–2012 by implementing liberal harvests of female moose. Elevated population‐wide twinning rates in 2012, 2015, 2017, and 2018, similar to elevated levels prior to 1997, were likely a positive response to lower moose densities and improved browse after wildfires. © 2018 The Wildlife Society.

Quantitative assessment of species identification in aerial transect surveys for ice‐associated seals

AbstractTechnological advances have facilitated collection of vast quantities of photographic data from aerial surveys of marine mammals. However, when it is difficult to distinguish species from a distance, reliable identification from aerial images can often be challenging. This is the case for ice‐associated seals, species for which global climate change has motivated intensive monitoring efforts in recent years. We assess species and age class identification from aerial images of four ice seal species (bearded seals, Erignathus barbatus; ribbon seals, Histriophoca fasciata; ringed seals, Pusa hispida; spotted seals, Phoca largha) in the Bering Sea. We also investigate the specific phenomenological and behavioral traits commonly associated with species identification and observer confidence. We generally found species and age class misidentification occurred at relatively low levels, but only 83% of spotted seals tended to be correctly identified (with 11% mistaken as ribbon seals). We also found certain traits were strong predictors for observed species, age class, or observer confidence. Our findings add to the growing body of evidence that species misidentification is pervasive in passive sampling of animal populations. Even low levels of misidentification have been demonstrated to induce substantial biases in estimators of species distribution and abundance, and it is important that statistical models account for such errors.

Population survey of Peary caribou (Rangifer tarandus pearyi) and muskoxen (Ovibos moschatus) on Banks Island, Northwest Territories, July 2010

We conducted a systematic aerial transect survey of Peary caribou (Rangifer tarandus pearyi) and muskoxen (Ovibus moschatus) on Banks Island, Northwest Territories, in July 2010. The population estimate of adult Peary caribou was 1097 ± 343 (95% Confidence Interval: CI), which is not significantly different from the 2005 estimate of 929 ± 289 (95% CI; P < 0.05). The current number, however, is a 4- to 9-fold decrease since the 1980s. The adult muskoxen population estimate was 36 676 ± 4031 (95% CI), which is significantly lower than the 2005 estimate of 47 209 ± 3997 (95% CI; P < 0.05).

Estimates of Duck Breeding Populations in the Nebraska Sandhills using Double Observer Methodology

Abstract. The Nebraska Sandhills are an important area for breeding ducks in the Great Plains, but reliable estimates of breeding populations are unavailable. Double-observer methodology was used to estimate abundance of breeding duck populations in the Nebraska Sandhills. Aerial transect surveys were conducted using methodology similar to the cooperative Waterfowl Breeding Population and Habitat Survey conducted by the U.S. Fish and Wildlife Service and Canadian Wildlife Service. Observations by two front-seat observers and one rear-seat observer were used to account for incomplete detectability. Transect-specific population size and detection probabilities were estimated using program SURVIV; estimates were species-specific by type of social grouping. Regional population sizes were obtained by extrapolating transects' estimates to the Sandhills. Detection probabilities were high (>0.75) for all species, but highest for Northern Shoveler (Anas clypeata) and Gadwall (A. strepera). Detection probabilities ...

Using Time Series to Estimate Rates of Population Change from Abundance Data

Abstract: Assessing the dynamics of wild populations often involves an estimate of the finite rate of population increase (λ) or the instantaneous rate of increase (r). However, a pervasive problem in trend estimation is that many analytical techniques assume independent errors among the observations. To be valid, variance estimates around λ (or r) must account for serial correlation that exists in abundance data. Time series analysis provides a method for estimating population trends and associated variances when serial correlation of errors occurs. We offer an approach and present an example for estimating λ and its associated variance when observations are correlated over time. We present a simplified time series method and variance estimator to account for autocorrelation based on a moving average process. We illustrate the procedure using a spectacled eider (Somateria fischeri) data set of estimated annual abundances from aerial transect surveys conducted from 1957 to 1995. The analytic variance estimator provides a way to plan future studies to reduce uncertainty and bias in estimates of population growth rates. Demographic studies with policy implications or those involving species of conservation concern should especially consider the correlated nature of population trend data.

Head to Head

White et al. (2005) estimated the area occupied by colonies of black-tailed prairie dog (Cynomys ludovicianus) in Colorado as 255,398 ha (95% CI of±9.5%) based on data collected with aerial transect surveys during 2001-2002 by staff of the Colorado Division of Wildlife (CDOW). During 2004 we conducted on-the-ground examinations of a sample of the colony intercept data used by White et al. (2005) and found evidence of misclassifications that would yield significant overestimation bias. We found that 25.4% of the total length of the colony intercepts we examined was incorrectly classified as being a prairie dog colony (these segments had no prairie dog burrows of any age). We also found that 50.3% of the length of examined intercepts fell on currently inactive colonies or portions of colonies (vacant burrows but no living prairie dogs) and only 24.3% fell on active prairie dog colonies with signs of living prairie dogs at our exami- nations 2 years after the survey reported by White et al. (2005). Further, in Bent and Kiowa counties, where plague (Yertsina pestus) and poisoning were active, we examined 36.9 km of reported active prairie dog intercepts and subjectively classified only 1.6% as active at normal-appearing prairie dog densities. Our fieldwork demonstrated that the estimate by White et al. (2005) was based on data with substantial errors as well as over- estimation biases that will be repeated if protocols are not modified for future surveys.

Effects of Petroleum Development on Terrain Preferences of Calving Caribou

We investigated terrain preferences of caribou (Rangifer tarandus granti) in an oilfield region near Prudhoe Bay, Alaska. Under disturbance-free conditions, the distribution of calving caribou determined by aerial transect surveys was correlated with indices of terrain ruggedness based on map contours. Caribou preferred quadrats dominated by fine-textured rugged terrain, particularly when present in large clusters, and avoided quadrats with flatter terrain. Displacement of maternal females from a zone within 4 km of roads and production-related facilities reduced use of rugged terrain types in that zone by 52%; the remaining preferred terrain was scattered and less accessible. This reduction was accompanied by a 43% increase in caribou use of rugged terrain 4-10 km from surface development. Given that terrain ruggedness is positively correlated with forage quality and biomass availability, combined underuse and overuse of these important habitats may compromise summer nutrition of lactating female caribou, thereby depressing body condition and, hence, subsequent reproductive success.

Evaluation of Aerial Transect Surveys of Mottled Ducks

Aerial counts of mottled ducks (Anas fulvlgula maculosil) along random transects were used to establish population Indices In Louisiana and southeastern Texas. Samples were stratified by habitat type, and replicated flights were made In February 1985, August 1985, and February 1986 to count mottled duck, occurring In strips on both sides of the air· craft. The August 1985 population Index was 173% greater than the Index of February 1985 and consistent with a post-breedlng season Increase In mottled duck numbers. The August survey also had a higher coefficient of variation, that probably resulted from the presence of large flocks of mottled ducks at that time of the year. The population Index Increased from 16,793 in February 1985 to 34,022 in February 1986. Other species of ducks were abundant In February, and observers had to differentiate between those species and mottled ducks. The mottled duck Index was greater in 100-m strips than 200-m strips, but the coefficients of variation were similar. The 100-m strip Is recommended for surveys made In February, because of the difficulty of differentiating mottled duck from other species at distances >100m.

Evaluation of Aerial Transects for Counting Wintering Mallards

Winter waterfowl surveys rarely use sampling methods, and little is Known about the precision and biases of their population estimates. Consequently, we developed aerial transect surveys (n=5) in 4 strata comprising 16 substrata in the lower Mississippi Alluvial Valley during winters 1987-88 through 198990 to estimate mallard (Anas platyrhynchos) population indices and determine regional patterns of habitat use. Mallard population indices ranged from 1,147,628 (SE=192,341) in December 1988 to 1,790,708 (SE=179,406) in January 1988

Evaluation of Aerial Transect Surveys for Wintering American Black Ducks

We used an experimental aerial transect survey with stratified random sampling, to estimate the size of the population of wintering black ducks (Anas rubripes) in coastal New Jersey during 2 winters, and the coastal Atlantic Flyway (Me. to S.C.) during 4 years. Population estimates were precise (CV 2 x MWS. Because of the lack of statistical design, precision cannot be estimated. Also, because an attempt is made to survey all waterfowl habitats and species, the results are likely not precise for any 1 species. Our objectives were to design a survey to provide precise estimates of the size of the Atlantic Flyway black duck population during winter, compare our results with those of the MWS during the same periods in terms of ac' Present address: Georgia Cooperative Fish and Wildlife Research Unit, School of Forest Resources, University of Georgia, Athens, GA 30602.

California Sea Lion Distribution: A Statistical Analysis of Aerial Transect Data

Sightings of California sea lions (Zalophus californianus) recorded on 23 aerial transect surveys of the Southern California Bight were pooled by 30' x 30' grid cells. Contour maps generated from celldensity estimates were used to represent seasonal distributions. The mean number of animals at sea in 3 seasons was calculated by summing cell population estimates, and the jackknife technique was used to place confidence limits on the at-sea component of the summer breeding population. California sea lions concentrate near their rookery islands and at specific open-water locations in summer. The center of their distribution shifts to the northwest in autumn and to the southeast in winter and spring, probably in response to prey availability. J. WILDL. MANAGE. 51(1):13-20 The California sea lion population in California is large and growing. Most breeding occurs on the southern California Channel Islands, where counts of pups show that the population doubled every 10 years since 1950 (Bonnell et al. 1984). Some of this growth may have resulted from immigration because counts of California sea lions at the 2 largest Mexican rookeries (Islas San Benito and Cedros) declined 40% between 1976 and 1981 (comparison of Jun counts) (Mate 1977, LeBoeuf et al. 1983). As of 1982, California sea lions on their southern California rookery islands totalled >50,000 animals (Heath and Francis 1983, Bonnell et al. 1984, Stewart and Yochem 1984). As the population in California has grown, California sea lions have been increasingly associated with fisheries conflicts, prompting an assessment of this species' status (see Demaster et al. [1982] for a review). Most knowledge of California sea lions is derived from studies of populations on land. Until recently, little was known about their habitat utilization and distribution at sea. Beginning in 1975, study was undertaken to map the distributi n at sea of all marine mammal species, including California sea lions, found in the Southern California Bight (SCB). Data were collected on 23 aerial surveys conducted over a 3-year period; each survey required about 20 hours in the air (Bonnell et al. 1980). From 1975 to 1978, 30,996 km (17,047 nautical miles) of trackline were flown. Our paper examines the pattern of California sea lion distribution in the SCB and places confidence limits on density values and population size estimates. Data were collected as part of the BLM-OCS Survey Program, supported by contracts between the U.S. Bur. Land Manage., U.S. Dep. Interior, and the Univ. California, Santa Cruz. The development of the distributional model was supported by a contract to WoodwardClyde Consultants (WCC), Walnut Creek, Calif., from the U.S. Minerals Manage. Serv. We are grateful to the many individuals involved in the collection of these data: D. H. Dettman, G. D. Farrens, C. B. Heath, B. J. LeBoeuf, and M. O. Pierson. We thank T. P. Winfield and R. This content downloaded from 207.46.13.111 on Tue, 09 Aug 2016 06:17:17 UTC All use subject to http://about.jstor.org/terms 14 SEA LION DISTRIBUTION * Bonnell and Ford J. Wildl. Manage. 51(1):1987 121

Biases in Aerial Transect Surveys for Moose during May and June

Precisions sur les biais methodologiques lors du denombrement par voie aerienne (methode des transects) d'Alces alces dans les basses terres des Tanana Flats, Alaska. La diminution de ces biais est possible mais augmenterait le cout de l'operation