Detection Probabilities of Ungulates in the Eastern Swaziland Lowveld

Collier, Bret A.; McCleery, Robert A.; Calhoun, Kirby W.; Roques, Kim G.; Monadjem, Ara

doi:10.3957/056.041.0106

Cited by 3 publications

(3 citation statements)

References 24 publications

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“…Although the detection values of all species except zebra were not statistically different across vegetation types, but were comparatively highest in grassland, and lowest in woodland, agreeing with Collier et al . (), who observed higher evidences of an increased detection in more open vegetation. The MANOVA results have suggested that differences in vegetation types and animal size as well as distance from transect line influenced the detection of animals.…”

Section: Discussionmentioning

confidence: 89%

“…) detection would be attained in ground transect surveys using a distance within 100 m in the western Serengeti and reliable estimates would not be obtained at distances exceeding 100 m especially for the small sized ungulates. Detections obtained here are, however, analogous to those obtained elsewhere with thermal imager and spotlight methods for a migrant species (wildebeest) and nonmigrant species (impala) (Collier et al ., ).…”

Section: Discussionmentioning

confidence: 97%

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Do animal size, seasons and vegetation type influence detection probability and density estimates of Serengeti ungulates?

et al. 2015

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Accurate detection of individual animals and estimation of ungulate population density might be a function of vegetation cover, animal size, observation radius or season. We assessed the effect of these factors on estimates of detection probability and density using five ungulate species in Western Serengeti National Park, Tanzania. Estimates were derived from information collected using ground surveys involving line transects targeting three resident species (impala, topi and buffalo) and two migrants (wildebeest and zebra) and analysed using DISTANCE, MANOVA, t-test and Pearson correlation. Results showed that ground surveys that take observation radii of 100 m would appreciably estimate at least 80% of the available ungulates. Beyond 100 m radii, surveys would leave approximately 43% of individuals undetected, the reason being a substantial influence of animal size, vegetation cover and observation radius on the detection. Animal size and observation radius have interactive effects. On their own seasonal differences, they do not have any effect but in interaction with animal size have significant effects especially on the migrant species. As reliable estimates of detection and density are required for making reasonable inferences, we urge that surveys using DISTANCE approach should consider incorporating both ground and aerial survey methods and ensure adequate sample replication.

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 97%

Do animal size, seasons and vegetation type influence detection probability and density estimates of Serengeti ungulates?

et al. 2015

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“…We encourage researchers to use this type of procedure instead of simple counts whenever possible, because situations are very rare that allow every individual to be detected 100% of the time when direct counts are made, even for large diurnal mammals (e.g. [90][91][92]) and, surprisingly, for plants (e.g. [93,94]).…”

Section: Detection-based Methods Of Estimating the Adult Sex Ratio From Unmarked Individualsmentioning

confidence: 99%

Estimating adult sex ratios in nature

Ancona

Dénes

Krüger

et al. 2017

Phil. Trans. R. Soc. B

111

123

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Adult sex ratio (ASR, the proportion of males in the adult population) is a central concept in population and evolutionary biology, and is also emerging as a major factor influencing mate choice, pair bonding and parental cooperation in both human and non-human societies. However, estimating ASR is fraught with difficulties stemming from the effects of spatial and temporal variation in the numbers of males and females, and detection/capture probabilities that differ between the sexes. Here, we critically evaluate methods for estimating ASR in wild animal populations, reviewing how recent statistical advances can be applied to handle some of these challenges. We review methods that directly account for detection differences between the sexes using counts of unmarked individuals (observed, trapped or killed) and counts of marked individuals using mark-recapture models. We review a third class of methods that do not directly sample the number of males and females, but instead estimate the sex ratio indirectly using relationships that emerge from demographic measures, such as survival, age structure, reproduction and assumed dynamics. We recommend that detection-based methods be used for estimating ASR in most situations, and point out that studies are needed that compare different ASR estimation methods and control for sex differences in dispersal.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

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