The Christmas Island blue-tailed skink (Cryptoblepharus egeriae): a survey protocol and an assessment of factors that relate to occupancy and detection

Smith, Michael J.; Boland, Christopher R. J.; Maple, Dion; Tiernan, Brendan

doi:10.18195/issn.0312-3162.27(1).2012.040-044

Cited by 2 publications

(4 citation statements)

References 4 publications

(3 reference statements)

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“…Today, survey protocols for many animals and even some plants incorporate corrections for detectability (e.g. [ 24 – 26 ]), but for large mammals, detectability is often ignored. To improve the reliability of data on mammal populations and aid in conservation efforts, we tested the accuracy of aerial surveys for large mammals using African savanna elephants ( Loxodonta africana ) as a study species.…”

Section: Introductionmentioning

confidence: 99%

Testing the Accuracy of Aerial Surveys for Large Mammals: An Experiment with African Savanna Elephants (Loxodonta africana)

2016

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Accurate counts of animals are critical for prioritizing conservation efforts. Past research, however, suggests that observers on aerial surveys may fail to detect all individuals of the target species present in the survey area. Such errors could bias population estimates low and confound trend estimation. We used two approaches to assess the accuracy of aerial surveys for African savanna elephants (Loxodonta africana) in northern Botswana. First, we used double-observer sampling, in which two observers make observations on the same herds, to estimate detectability of elephants and determine what variables affect it. Second, we compared total counts, a complete survey of the entire study area, against sample counts, in which only a portion of the study area is sampled. Total counts are often considered a complete census, so comparing total counts against sample counts can help to determine if sample counts are underestimating elephant numbers. We estimated that observers detected only 76% ± SE of 2% of elephant herds and 87 ± 1% of individual elephants present in survey strips. Detectability increased strongly with elephant herd size. Out of the four observers used in total, one observer had a lower detection probability than the other three, and detectability was higher in the rear row of seats than the front. The habitat immediately adjacent to animals also affected detectability, with detection more likely in more open habitats. Total counts were not statistically distinguishable from sample counts. Because, however, the double-observer samples revealed that observers missed 13% of elephants, we conclude that total counts may be undercounting elephants as well. These results suggest that elephant population estimates from both sample and total counts are biased low. Because factors such as observer and habitat affected detectability of elephants, comparisons of elephant populations across time or space may be confounded. We encourage survey teams to incorporate detectability analysis in all aerial surveys for mammals.

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Section: Introductionmentioning

confidence: 99%

Testing the Accuracy of Aerial Surveys for Large Mammals: An Experiment with African Savanna Elephants (Loxodonta africana)

2016

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“…(during the daytime 8:00-11:30) (see Table 2 for a summary of the counts of each species during our surveys). The combination of transect and visual encounter surveys is known to be effective in detecting reptiles in tropical environments (Doan 2003;McDiarmid et al 2011;Smith et al 2012a).…”

Section: Standardised Rapid Biological Assessment: a Time-limited Appmentioning

confidence: 99%

“…Time-limited transects do not neccesarily require repeated survey occasions (Catenazzi et al 2016), but our repeated surveys allowed us to estimate both the abundance and the probability of individual detection of alien reptiles via hierarchical models (Royle 2004;Kéry and Royle 2016;Ficetola et al 2018). Our time-limited approach was a minor modification of the methodology employed by Christmas Island National Park Staff to survey for both native and alien reptiles on the island (Smith et al 2012a(Smith et al , 2012b. Therefore, our time-limited methodology aligns well with pre-existing protocols, which can be easily adapted to inform the management of alien reptiles.…”

Section: Standardised Rapid Biological Assessment: a Time-limited Appmentioning

confidence: 99%

“…Reptiles are a notable group of emergent alien species responsible for serious environmental impacts in recipient regions worldwide, especially on islands (Rodda et al 1999;Christy et al 2010;Powell 2011;Smith et al 2012a;Kraus 2015). Alien reptiles are frequently transported both unintentionally (i.e., as stowaways) and intentionally (e.g., through the pet trade), and the accelerating volume of global traffic has increased their opportunities for introduction into new regions (Kraus 2009;Powell 2011;Helmus et al 2014;Capinha et al 2017;Moser et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Low detectability of alien reptiles can lead to biosecurity management failure: a case study from Christmas Island (Australia)

García‐Díaz¹,

Ross²,

Vall‐llosera³

et al. 2019

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When we assume that contemporary management actions will be effective against the global rise of emerging alien species, we can develop management complacency, which leads to potentially disastrous outcomes for native biodiversity. Here, we propose the use of the probability of detection as a metric to assess the feasibility of management actions for alien species. We explore how detectability can influence the management of alien reptiles, a group of emergent alien vertebrates globally. We use a Rapid Biological Assessment method (time-limited transects) to estimate the probability of detection for alien reptiles present on Christmas Island (Australia). Across the five species studied, we found low probabilities of detection and poor explanatory capacity of the individual covariates included in our models. These findings indicate that management options to deal with alien reptiles are limited due to the potential high cost and low efficacy associated with low probabilities of detection. Strict preventive strategies, firmly espousing the principles of adaptiveness and precautionary policies, combined with early detection and biosecurity response activities are needed to address the emergence of alien reptiles. Our research was focussed on alien reptiles on islands, but the rise of new pools of alien species from all taxonomic realms across the world suggests that our conclusions may be applicable more generally. Further research is called for to explore the applicability of our conclusions and recommendations to other taxonomic groups and regions of the world. A peer-reviewed open-access journal NeoBiotaPablo García-Díaz et al. / NeoBiota 45: 75-92 (2019) 76

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The Christmas Island blue-tailed skink (Cryptoblepharus egeriae): a survey protocol and an assessment of factors that relate to occupancy and detection

Cited by 2 publications

References 4 publications

Testing the Accuracy of Aerial Surveys for Large Mammals: An Experiment with African Savanna Elephants (Loxodonta africana)

Testing the Accuracy of Aerial Surveys for Large Mammals: An Experiment with African Savanna Elephants (Loxodonta africana)

Low detectability of alien reptiles can lead to biosecurity management failure: a case study from Christmas Island (Australia)

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