A Note on the Sightability of Emus During an Aerial Survey

1988 ◽  
Vol 15 (6) ◽  
pp. 647 ◽  
Author(s):  
J Hone ◽  
J Short
Keyword(s):  
Cloud Cover ◽  
Weighted Average ◽  
Limited Range ◽  
Aerial Survey ◽  
Time Of Day ◽  
True Density ◽  
Aerial Surveys ◽  
Dromaius Novaehollandiae ◽  
Survey Estimates

Observed densities of emus, Dromaius novaehollandiae, estimated from aerial surveys were compared with results of a drive count in 1985 and 1986. The study area was mostly open shrubland. True density of emus was 2.56 per km2 in 1985 and 1.15 per km2 in 1986. Aerial survey estimates were 66 and47% oftrue density in the two years, respectively, and the weighted average was 60%. Over the limited range tested ofeach variable, observed density was not significantly affected by temperature, cloud cover or time of day.

Some human, aircraft and animal factors affecting aerial surveys: how to enumerate animals from the air

2008 ◽  
Vol 35 (4) ◽  
pp. 258 ◽  
Author(s):  
Peter J. S. Fleming ◽  
John P. Tracey
Keyword(s):  
Visual Acuity ◽  
New South ◽  
Human Memory ◽  
Aerial Survey ◽  
Factors Affecting ◽  
Counting Error ◽  
Aerial Surveys ◽  
South Wales ◽  
Survey Estimates ◽  
Aerial Platforms

Aerial surveys of wildlife involve a noisy platform carrying one or more observers moving over animals in order to quantify their abundance. This simple-sounding system encapsulates limits to human visual acuity and human concentration, visual attention, salience of target objects within the viewed scene, characteristics of survey platforms and facets of animal behaviours that affect the detection of animals by the airborne observers. These facets are too often ignored in aerial surveys, yet are inherent sources of counting error. Here we briefly review factors limiting the ability of observers to detect animals from aerial platforms in a range of sites, including characteristics of the aircraft, observers and target animals. Some of the previously uninvestigated limitations identified in the review were studied in central and western New South Wales, showing that inaccuracies of human memory and enumeration processes are sources of bias in aerial survey estimates. Standard protocols that minimise or account for the reviewed factors in aerial surveys of wildlife are recommended.

Variation in harbour seal counts obtained using aerial surveys

2010 ◽  
Vol 90 (8) ◽  
pp. 1659-1666 ◽  
Author(s):  
Louise Cunningham ◽  
John M. Baxter ◽  
Ian L. Boyd
Keyword(s):  
Aerial Survey ◽  
Specific Model ◽  
Time Of Day ◽  
Harbour Seal ◽  
Survey Period ◽  
North West ◽  
Aerial Surveys ◽  
Harbour Seals ◽  
The Uk ◽  
Post Hoc

Aerial surveys of harbour seals (Phoca vitulina) are usually carried out to provide an index of population size. This can be normalized, either by design or by post-hoc analysis to reduce the effects that date, time of day, tide and weather might have on the number of seals counted. In order for long-term trends to be determined from these counts it is assumed that the mean number of seals at a particular site does not vary during the survey period, and that the start and duration of the survey window does not vary with location or between years. This study used a combination of repeat land-based and aerial surveys to test the assumption for constancy of counts during the survey period. The study focused on harbour seal abundance at haul-out sites around the Isle of Skye in north-west Scotland. The coefficient of variation in these counts was estimated to be 15%, based on repeat aerial surveys using thermal imaging. Land-based counts were used to examine the effect of covariates on seal numbers using generalized additive modelling. This site-specific model predicted that the current aerial survey window for harbour seals in the UK, which is a three-week period during the moult, is about a week too early and that count variation could be reduced by surveying 1 1/2 hours earlier in the tidal cycle. Furthermore, the pupping period showed even higher (though more variable) abundance of hauled out seals than during the moult.

Correcting for Incomplete Sighting in Aerial Surveys of Kangaroos

1986 ◽  
Vol 13 (3) ◽  
pp. 339 ◽  
Author(s):  
A Barnes ◽  
GJE Hill ◽  
GR Wilson
Keyword(s):  
Species Differences ◽  
Aerial Survey ◽  
Time Of Day ◽  
Correction Factors ◽  
Density Estimates ◽  
Mathematical Properties ◽  
Aerial Surveys ◽  
Alternative Method ◽  
Management Procedures ◽  
Continued Use

Kangaroo density estimates derived from aerial survey depend on the method of deriving sightability correction factors developed by Caughley. The method depends on five assumptions, some concerned with the mathematical properties of a model for sightability probabilities and others with deriving correction factors from this model. All these assumptions can be criticized. In addition, evidence on the performance of the method does not suggest that it is accurate. Published density estimates are less precise than indicated, and may include biases due to factors not considered in the correction factors used, e.g. seasonal conditions, time of day, and species differences. At present, no satisfactory alternative method of correction exists but, because inaccuracies may be large, continued use of the method requires much greater caution than has previously been shown. This is particularly relevant where density estimates are used to determine management procedures.

Estimating kangaroo density by aerial survey: a comparison of thermal cameras with human observers

2019 ◽  
Vol 46 (8) ◽  
pp. 639 ◽  
Author(s):  
Mark Lethbridge ◽  
Michael Stead ◽  
Cameron Wells
Keyword(s):  
Thermal Imaging ◽  
Imaging Techniques ◽  
Population Data ◽  
Aerial Survey ◽  
Time Of Day ◽  
Human Observer ◽  
Thermal Camera ◽  
Density Estimates ◽  
Aerial Surveys ◽  
Animal Populations

Abstract ContextAerial surveys provide valuable information about the population status and distribution of many native and pest vertebrate species. They are vital for evidence-based monitoring, budget planning and setting management targets. Despite aircraft running costs, they remain one of the most cost-effective ways to capture distribution and abundance data over a broad area. In Australia, annual surveys of large macropods are undertaken in several states to inform management, and in some jurisdictions, to help set commercial kangaroo harvest quotas. Improvements in the cost efficiencies of these surveys are continually sought. Aerial thermal imaging techniques are increasingly being tested for wildlife surveys, but to date no studies have directly compared population data derived from thermal imaging with data collected by human observers during the same flight. AimsDuring an aerial survey of western grey kangaroos (Macropus fuliginosus), eastern grey kangaroos (M. giganteus) and red kangaroos (Osphranter rufus) across the state of Victoria, Australia, the objective was to conduct a direct comparison of the effectiveness of thermal camera technology and human observers for estimating kangaroo populations from aerial surveys. MethodsA thermal camera was mounted alongside an aerial observer on one side of the aircraft for a total of 1360km of transect lines. All thermal footage was reviewed manually. Population density estimates and distance sampling models were compared with human observer counts. Key resultsOverall, the kangaroo density estimates obtained from the thermal camera data were around 30% higher than estimates derived from aerial observer counts. This difference was greater in wooded habitats. Conversely, human-derived counts were greater in open habitats, possibly due to interference from sunlight and flushing. It was not possible to distinguish between species of macropod in the thermal imagery. ConclusionsThermal survey techniques require refining, but the results of the present study suggest that with careful selection of time of day for surveys, more accurate population estimates may be possible than with conventional aerial surveys. ImplicationsConventional aerial surveys may be underestimating animal populations in some habitats. Further studies that directly compare the performance of aerial observers and thermal imaging are required across a range of species and habitats.

scholarly journals Surfacing and vertical behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Mediterranean Sea: implications for aerial surveys

2020 ◽  
Vol 77 (5) ◽  
pp. 1979-1991
Author(s):  
Robert Klaus Bauer ◽  
Fabien Forget ◽  
Jean-Marc Fromentin ◽  
Manuela Capello
Keyword(s):  
Mediterranean Sea ◽  
Fork Length ◽  
Bluefin Tuna ◽  
Aerial Survey ◽  
Thunnus Thynnus ◽  
Survey Period ◽  
Atlantic Bluefin Tuna ◽  
Aerial Surveys ◽  
Gulf Of Lion ◽  
Nw Mediterranean

Abstract Atlantic bluefin tuna (Thunnus thynnus) (ABFT) frequently engage in surface basking and foraging behaviour that makes them detectable from afar. This behaviour is utilized for the development of fisheries-independent abundance indices based on aerial surveys, although changes in the surface-feeding dynamics of ABFT are not yet accounted for. We investigated the daytime surfacing behaviour of ABFT at different temporal and vertical resolutions based on 24 individuals (117–158 cm fork length), tagged with pop-up archival tags in the Gulf of Lion, NW-Mediterranean Sea between 2015 and 2016. The results suggest that ABFT remain usually <2 min continuously within the visible surface (0–1 m) during daytime. ABFT presence in the 0–1 and 0–20 m layers varied over time and between individuals but showed a seasonal decline towards autumn with the breakdown of thermal stratification. Furthermore, the rate of surfacing events was highly correlated with the time spent in the 0–20 m layer. Geolocation estimates confirm a strong site fidelity of ABFT during the aerial survey period (August–October) in the Gulf of Lion. Our results support the choice of the survey region and period, but related indices should account for the seasonality of ABFT surface behaviour [i.e. the time spent in the 0–20 m layer.

scholarly journals Boreal old-growth forest structural diversity challenges aerial photographic survey accuracy

2020 ◽  
Vol 50 (2) ◽  
pp. 155-169 ◽  
Author(s):  
Maxence Martin ◽  
Nicole J. Fenton ◽  
Hubert Morin
Keyword(s):  
Sustainable Forest Management ◽  
Forest Succession ◽  
Structural Diversity ◽  
Aerial Survey ◽  
Old Growth ◽  
Tree Species Composition ◽  
Forest Inventories ◽  
Old Growth Forest ◽  
Aerial Surveys ◽  
Old Growth Forests

The erosion of old-growth forests in boreal managed landscapes is a major issue currently faced by forest managers; however, resolving this problem requires accurate surveys. The intention of our study was to determine if historic operational aerial forest surveys accurately identified boreal old-growth forests in Quebec, Canada. We first compared stand successional stages (even-aged vs. old-growth) in two aerial surveys performed in 1968 (preindustrial aerial survey) and 2007 (modern aerial survey) on the same 2200 km2 territory. Second, we evaluated the accuracy of the modern aerial survey by comparing its results with those of 74 field plots sampled in the study territory between 2014 and 2016. The two aerial surveys differed significantly; 80.8% of the undisturbed stands that were identified as “old-growth” in the preindustrial survey were classified as “even-aged” in the modern survey, and 60% of the stands identified as “old-growth” by field sampling were also erroneously identified as “even-aged” by the modern aerial survey. The scarcity of obvious old-growth attributes in boreal old-growth forests, as well as poorly adapted modern aerial survey criteria (i.e., criteria requiring high vertical stratification and significant changes in tree species composition along forest succession), were the main factors explaining these errors. It is therefore likely that most of Quebec’s boreal old-growth forests are currently not recognized as such in forest inventories, challenging the efficacy of sustainable forest management policies.

On bias, precision and accuracy in wildlife aerial surveys

2008 ◽  
Vol 35 (4) ◽  
pp. 253 ◽  
Author(s):  
Jim Hone
Keyword(s):  
Survey Data ◽  
Wildlife Management ◽  
Aerial Survey ◽  
Review Of The Literature ◽  
Density Estimates ◽  
True Value ◽  
Wildlife Population ◽  
Aerial Surveys ◽  
Precision And Accuracy ◽  
Definition Of

Bias, precision and accuracy have been studied extensively in wildlife population estimation including aerial surveys. A review of the literature shows that the concepts of bias and precision are used broadly consistently. Aerial survey data from known populations of feral pig carcases and white-tailed deer show that few density estimates are unbiased and precise. Research is needed, however, to clarify how much bias and how much precision are enough for the various types of wildlife management activities. Accuracy is used in two closely related but different ways. One set of definitions of accuracy relates to deviations from the true value (bias) and the second set relates to squared deviations from the true value (bias and precision). The implications are that authors are encouraged to clearly state which definition of accuracy they use, or focus solely on bias and precision.

Calibrating Aerial Surveys of Kangaroos by Comparison With Drive Counts

1988 ◽  
Vol 15 (3) ◽  
pp. 277 ◽  
Author(s):  
J Short ◽  
J Hone
Keyword(s):  
Aerial Survey ◽  
Survey Area ◽  
Aerial Surveys ◽  
Drive Counts

Densities of red and western grey kangaroos and euros were assessed by aerial survey and compared with densities obtained in the same area by drive counts. The survey area (12.1 km2) was long, narrow and sparsely vegetated. Lakes and a kangaroo-proof fence bounded the area on three sides facilitating the drive count. Densities from aerial surveys ranged between 38 and 54% of the corresponding drive counts for red kangaroos, between 15 and 23% for western grey kangaroos, and between 9 and 10% for euros. The time of morning at which the surveys were conducted altered these percentages. About twice as many red and western grey kangaroos were counted on aerial surveys at sunrise compared to surveys 3.5 h later.

Accuracy of the Multiple-Regression Method for Estimating Population-Density in Strip Transects

1986 ◽  
Vol 13 (2) ◽  
pp. 121 ◽  
Author(s):  
J Hone
Keyword(s):  
Population Density ◽  
Multiple Regression ◽  
Robust Estimation ◽  
Aerial Survey ◽  
Regression Method ◽  
Regression Equations ◽  
Regression Analyses ◽  
True Density ◽  
Balanced Design ◽  
Multiple Regression Method

Two experiments examined the accuracy of the multiple regression method for estimating population density. In experiment I , in a balanced design, an observer counted objectsin simulated strip transects. Multiple regression analyses yielded accurate estimates when true density was low, and overestimated density when true density was high. Regression equations calculated at each level of true density varied from linear to quadratic. A simple polynomial model accurately estimated true density. In experiment 2 an aerial survey of sheep showed that estimated density was highly significantly (P <0.001) different from true density. The results suggest that greater use should be made of established criteria for robust estimation of true density in transect studies.

Studies of Dugons at Shark Bay, Western Australia I. Analysis of Population Size, Composition, Dispersion and Nabitat USe on the Basis of Aerial Survey

1982 ◽  
Vol 9 (1) ◽  
pp. 69 ◽  
Author(s):  
PK Anderson
Keyword(s):  
Population Size ◽  
Western Australia ◽  
Cloud Cover ◽  
Size Composition ◽  
Aerial Survey ◽  
Vegetation Patterns ◽  
Depressing Effect ◽  
Shark Bay ◽  
Or Groups ◽  
Analysis Of Dispersion

In midwinter dugongs concentrate in western Shark Bay, adjacent to Dirk Hartog I., although scattered individuals or groups remain in other regions. Up to 496 dugongs were counted in intensively surveyed western areas in July 1979. At least 553 individuals are calculated to have been present in the region, and a minimum population of over 900 individuals estimated for the Bay as a whole. The population seems to be a well defined isolate, and is relatively undisturbed. Conditions are very favourable for more detailed study. A method for estimating the number of animals overlooked in the blind zone directly beneath the aircraft is described. Aerial counts of dugongs varied greatly with conditions. Cloud cover had a large depressing effect: surface turbulence and subsurface turbidity were less significant. Dugong activity is concentrated on the sublittoral platform. Sites of major aggregation may not be the same in successive years. Locally favoured habitats are at the seaward margins of the sublittoral platform, and on offshore shoals. Vegetation patterns at favoured sites may reflect dugong grazing. Persistent use of favoured localities, and local shifts in concentration were observed. Distribution of other large vertebrates, and of boats, relative to that of dugongs was examined and a significant correlation between sightings of large sharks and larger aggregations of dugongs was found. Analysis of dispersion revealed that most dugongs were in groups although most sightings were of single individuals. Cows with calves were less likely to be in the company of other dugongs than were adults without calves. From ll to 12% of individuals were calves.

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