Precision of helicopter-based total-area counts of large ungulates in bushveld

Reilly, Brian K.

doi:10.4102/koedoe.v45i2.33

Cited by 8 publications

(9 citation statements)

References 14 publications

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“…Aerial surveys allow the estimation of population numbers for species distributed over vast areas and in remote habitats. Their accuracy, however, has been questioned (Seber 1992, Reilly and Hensbergen 2002, Bender et al 2003 because they commonly underestimate population sizes, and sightability varies greatly among years and among age and sex classes (Wolfe and Kimball 1989, Woolley and Lindzey 1997, Gonzalez-Voyer et al 2001.…”

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confidence: 99%

Population Dynamics and Harvest Potential of Mountain Goat Herds in Alberta

Hamel¹,

Côté²,

Smith³

et al. 2006

Journal of Wildlife Management

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The understanding of population dynamics is a central issue for managing large mammals. Modeling has allowed population ecologists to increase their knowledge about complex systems and better predict population responses to diverse perturbations. Mountain goats (Oreamnos americanus) appear sensitive to harvest, but the relative influence of survival and reproductive rates on their population dynamics are not well understood. Using longitudinal data on age‐ and sex‐specific survival and reproduction from a marked mountain goat population in Alberta, Canada, we built a stage‐class matrix model to predict short‐term numerical changes for 11 other goat populations in Alberta for which the only data available were from annual aerial surveys. Overall, the model provided an acceptable fit to changes in population size for 8 of 12 populations. Temporal trends in population size were underestimated in 2 populations and overestimated in another 2, suggesting that these populations had different vital rates than those of the intensively studied population. Sensitivity analyses revealed that the survival of mature females (aged 5 yr and older) had the greatest elasticity for population growth. Modeled management scenarios indicated that nonselective yearly harvest rates above 1% of goats aged 2 years and older were not sustainable over the short‐term for some populations. The simulations also revealed that small (n = 25) and medium‐size (n = 50) populations, which correspond to most goat populations in Alberta, had high extinction risk (18 to 82% over 40 years), even in the absence of harvest. Our results confirm that mountain goat populations are very sensitive to harvest, indicate that wildlife managers should prevent female harvest, and suggest that although a high demand for goat hunting exists in Alberta, most populations in this province—and probably small populations elsewhere—cannot withstand exploitation.

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confidence: 99%

Population Dynamics and Harvest Potential of Mountain Goat Herds in Alberta

Hamel¹,

Côté²,

Smith³

et al. 2006

Journal of Wildlife Management

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“…Alternatively, caribou may alter their behavior with varying flight altitude and speed as a response to noise disturbance (Reimers and Colman ), thereby altering their probability of detection. Population estimates also decreased with distance flown ( p area ), which might indicate a trade‐off between effort and observer fatigue (Reilly and van Hensbergen ). If the minimum distance flown was sufficient to detect most visible animals, and observers missed relatively more animals later in long surveys because of fatigue, then counts may have been lower than expected in longer surveys.…”

Section: Discussionmentioning

confidence: 99%

Detecting a population decline of woodland caribou (Rangifer tarandus caribou) from non‐standardized monitoring data in Pukaskwa National Park, Ontario

et al. 2014

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Observation bias from methodological inconsistencies plague many long-term ecological monitoring studies, leaving land managers to question the validity of apparent population trends over time. Furthermore, some species are cryptic and have low detectability, so assessments are naturally imprecise. We assessed the utility of aerial surveys for woodland caribou from 1972 to 2009 at a Canadian national park in detecting a reliable population trend for this threatened species. The surveys varied in flight patterns, total distance flown, observer experience, speed, altitude, timing, temperature, and snow depth. Of these, distance and the speed/altitude index influenced the population estimates, whereas no variables influenced the calf: female ratio or winter range size. Year was included in all plausible models for population estimates, and the majority of plausible models for calf:female ratio and winter range size. Population size, recruitment and winter range size all declined over time in the respective models with the lowest AIC c . Switching methodologies mid-way through a long-term aerial survey monitoring program creates greater complexity for trend analysis over time; however, this study suggests that reliable conclusions can still be drawn from long-term monitoring data if confounding factors are accounted for in the analysis. Ó 2014 The Wildlife Society.

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“…If the objective of censusing is the determination of trends in animal numbers rather than absolute abundance, counting error is acceptable provided the survey is regularly repeated under similar conditions (Eiselen 1994;Reilly 2002). If however the aim is determination of absolute abundance, errors in counting need to be quantified and corrected for (Jolly 1969;Porteus et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Conducting animal censuses amongst abrupt topography; aGIS‐based alternative toDistance

2014

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Management often bases decisions on estimates of animal density and population size. Aerial sampling is expensive whilst current ground methods, noticeably Distance sampling, assume a single detection function for each habitat and that visibility in a given habitat type declines in a smooth, increasing manner with distance from the observer. If the visibility within a habitat varies widely or is suddenly cut off, as amongst abrupt topography, these assumptions are invalidated. We present an affordable, accessible and accurate method for conducting repeated annual censuses on large herbivores in such terrain.We used a GIS habitat-based approach. Monthly, over a two year period, we conducted repeated road transects in Ithala Game Reserve, South Africa, using GPS to record the geographic position of each sighting.These records (n = 8742) were then imported into a GIS and overlaid onto an existing habitat-type GIS layer.With the sampled area thus defined as an irregular polygon in the GIS encompassing all records, we calculated densities of each herbivore species by habitat type and extrapolated total population size estimates. Estimates of maximum population size for wildebeest and zebra correlated (±15%) with management's estimates based on aerial surveys, walked transects and experience.White rhino are individually counted in the reserve and our estimates (year 1: 52; year 2: 57) matched these known numbers (year 1: 50; year 2: 53). Our method also yielded realistic numbers for impala, but unrealistic numbers for kudu and warthog. Our GIS-based census technique produced realistic maximum population estimates for abundant grazing and mixed-feeder mesoherbivores and for scarce, but highly visible, megaherbivores, but not for cryptic species.With the increasing availability of GIS data, the technique is recommended to those working in abrupt terrain frustrated by the inability of current ground census techniques, principally Distance sampling, to produce realistic population estimates.

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Precision of helicopter-based total-area counts of large ungulates in bushveld

Cited by 8 publications

References 14 publications

Population Dynamics and Harvest Potential of Mountain Goat Herds in Alberta

Population Dynamics and Harvest Potential of Mountain Goat Herds in Alberta

Detecting a population decline of woodland caribou (Rangifer tarandus caribou) from non‐standardized monitoring data in Pukaskwa National Park, Ontario

Conducting animal censuses amongst abrupt topography; aGIS‐based alternative toDistance

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