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Estimating Sightability for Helicopter Surveys Using Surrogates of White-Tailed Deer
Journal of Wildlife Management ( IF 2.3 ) Pub Date : 2021-04-01 , DOI: 10.1002/jwmg.22040
JORDAN R. DYAL 1 , Karl V. Miller 1 , Michael J. Cherry 2 , Gino J. D'Angelo 1
Affiliation  

On large management units where terrain allows observation of white-tailed deer (Odocoileus virginianus) from the air, helicopter surveys may provide managers with cost-effective and accurate estimates of population abundance; however, imperfect detection of deer introduces negative bias. This can result in potentially inappropriate management recommendations (e.g., harvest prescriptions). Sightability estimators are designed to model detection heterogeneity based on factors that affect observer detection of target animals. Sightability models are widely used to estimate ungulate abundance; however, previous researchers have developed sightability models using radio-collared animals, potentially introducing bias during model development attributed to unaccounted for movement between initial and follow-up flights. Therefore, our objectives were to model detection probability using surrogates of white-tailed deer as a function of covariates including distance from transect, vegetative obstruction, and light conditions to improve population estimates derived from helicopter surveys and apply our final sightability model in operational helicopter surveys. We conducted our study in 2019 on a 399.4-km2 study area within a 1,210-km2 cattle ranch in central Florida, USA. We placed 3-dimensional archery targets as surrogates for white-tailed deer at assigned locations unknown to observers across a combination of stratified bins of vegetative obstruction and distances from the transect. Our top model indicated that distance from the transect and vegetative obstruction negatively affected detection of deer. Detection probability on the flight transect ranged from 0.95 (95% CI = 0.89–0.98) for vegetative obstruction 0–25% and distance from transect 0–25 m to 0.05 (95% CI = 0.01–0.18) for vegetative obstruction 76–100% and distance from transect 100–125 m. We applied our sightability model to operational surveys on 3 units, which produced population estimates averaging 26% higher than those derived from uncorrected counts. Observers simultaneously recorded live deer during operational flights, of which 60% of deer groups were observed while stationary. Our methods using stationary surrogates to develop region-specific sightability models could be used in other study areas to account for imperfect detection of white-tailed deer. © 2021 The Wildlife Society.

中文翻译:

使用白尾鹿的替代物估计直升机调查的可见性

在地形允许观察白尾鹿(Odocoileus virginianus)的大型管理单位) 从空中,直升机调查可以为管理人员提供具有成本效益和准确的人口丰度估计;然而,对鹿的不完美检测会引入负偏差。这可能导致潜在的不适当的管理建议(例如,收获处方)。可视性估计器旨在根据影响目标动物观察​​者检测的因素对检测异质性进行建模。可视性模型被广泛用于估计有蹄类动物的数量;然而,之前的研究人员已经使用带无线电项圈的动物开发了可视性模型,这可能会在模型开发过程中引入偏差,原因是初始飞行和后续飞行之间的移动不明。所以,我们的目标是使用白尾鹿的替代品对检测概率进行建模,作为协变量的函数,包括与横断面的距离、植物障碍和光照条件,以改进从直升机调查中得出的种群估计数,并将我们的最终可视性模型应用于运营直升机调查。我们于 2019 年在 399.4 公里的公路上进行了研究2研究区域内 1,210 公里2美国佛罗里达州中部的牧场。我们将 3 维射箭目标作为白尾鹿的替代品放置在观察者未知的指定位置,跨越植被障碍的分层箱和与横断面的距离的组合。我们的顶级模型表明,与横断面的距离和植物障碍会对鹿的检测产生负面影响。飞行样带上的检测概率范围为 0.95 (95% CI = 0.89-0.98) 植物性障碍 0-25% 和横断面距离 0-25 m 到 0.05 (95% CI = 0.01-0.18) 植物性障碍 76-100 % 和距横断面 100–125 m 的距离。我们将我们的可视性模型应用于 3 个单位的运营调查,产生的人口估计数比未校正计数得出的人口估计数平均高出 26%。观察者在操作飞行期间同时记录了活鹿,其中 60% 的鹿群是在静止时观察到的。我们使用固定代理来开发特定区域的可视性模型的方法可用于其他研究领域,以解决对白尾鹿的不完美检测。© 2021 野生动物协会。
更新日期:2021-04-01
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