Territory monitoring of Tawny Owls Strix aluco using playback calls is a reliable population monitoring method

Population monitoring of brushtail possums (Trichosurus vulpecula) is an essential part of their management in New Zealand, with a trap-catch removal method being used most commonly. An alternative monitoring method (bait-interference), using bite marks on wax blocks, has been promoted as a more cost-effective alternative to using traps. However, neither of these methods has been validated. We assessed the utility of these two methods regarding their accuracy (unbiasedness and precision) in detecting changes in possum abundance by comparing the estimates of relative change in possum density following control obtained from both methods with the kill rate among radio-collared possums in the same study areas. In each of seven control operations, 48–50 possums were collared with mortality-sensing radio-transmitters, and trap-catch and wax-block lines were assessed before and after control. The correlation between trap-catch and radio-transmitter kill estimates (R2 = 0.91) suggests that trap catch, as currently used to monitor relative possum abundance, appears to be sufficiently accurate to manage these pests, with any bias being small. The kill estimates based on the wax-block monitoring were correlated less strongly with the radiotransmitter estimates than the trap-catch estimates (R2 = 0.66), although still significant. Until the extent of the potential bias in the wax-block estimates is known, we recommend that traps continue to be used as the main method to monitor possum abundance.

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Learning to count: adapting population monitoring for Endangered huemul deer Hippocamelus bisulcus to meet conservation objectives

10.26686/wgtn.12971876 ◽

2020 ◽

Author(s):

Heiko Wittmer ◽

P Corti ◽

C Saucedo ◽

J Galaz

Keyword(s):

Survey Data ◽

Survey Methods ◽

Cost Effective ◽

Population Monitoring ◽

Population Trends ◽

Monitoring Methods ◽

Monitoring Method ◽

Hippocamelus Bisulcus ◽

Detection Probabilities ◽

Current Survey

Considerable efforts have been invested in recent years to improve methods for both data collection and analyses required for population monitoring. Where historical or current estimates of population size are not adjusted for detection probabilities they may be too inaccurate to provide meaningful estimates of trends and thus monitoring methods need to be adapted. Here, we use data from the Endangered huemul deer Hippocamelus bisulcus to outline a framework to develop accurate robust estimates of detection probabilities that can be incorporated into new surveys in a cost-effective way and applied to existing survey data sets. In particular, by retroactively estimating detection probabilities for surveys of huemul, we show that current survey methods for huemul are inadequate to determine population trends reliably. Based on these results we propose a new monitoring method for the huemul and discuss the importance of estimating accuracies of historical survey data to ensure that changes in the abundance of the species reflect real population trends and are not an artefact of variation over time in the accuracy of survey data. © 2010 Fauna & Flora International.

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Learning to count: adapting population monitoring for Endangered huemul deer Hippocamelus bisulcus to meet conservation objectives

10.26686/wgtn.12971876.v1 ◽

2020 ◽

Author(s):

Heiko Wittmer ◽

P Corti ◽

C Saucedo ◽

J Galaz

Keyword(s):

Survey Data ◽

Survey Methods ◽

Cost Effective ◽

Population Monitoring ◽

Population Trends ◽

Monitoring Methods ◽

Monitoring Method ◽

Hippocamelus Bisulcus ◽

Detection Probabilities ◽

Current Survey

Considerable efforts have been invested in recent years to improve methods for both data collection and analyses required for population monitoring. Where historical or current estimates of population size are not adjusted for detection probabilities they may be too inaccurate to provide meaningful estimates of trends and thus monitoring methods need to be adapted. Here, we use data from the Endangered huemul deer Hippocamelus bisulcus to outline a framework to develop accurate robust estimates of detection probabilities that can be incorporated into new surveys in a cost-effective way and applied to existing survey data sets. In particular, by retroactively estimating detection probabilities for surveys of huemul, we show that current survey methods for huemul are inadequate to determine population trends reliably. Based on these results we propose a new monitoring method for the huemul and discuss the importance of estimating accuracies of historical survey data to ensure that changes in the abundance of the species reflect real population trends and are not an artefact of variation over time in the accuracy of survey data. © 2010 Fauna & Flora International.

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Learning to count: adapting population monitoring for Endangered huemul deer Hippocamelus bisulcus to meet conservation objectives

Oryx ◽

10.1017/s0030605310001018 ◽

2010 ◽

Vol 44 (4) ◽

pp. 516-522 ◽

Cited By ~ 8

Author(s):

Heiko U. Wittmer ◽

Paulo Corti ◽

Cristián Saucedo ◽

José Luis Galaz

Keyword(s):

Survey Data ◽

Survey Methods ◽

Cost Effective ◽

Population Monitoring ◽

Population Trends ◽

Monitoring Methods ◽

Monitoring Method ◽

Hippocamelus Bisulcus ◽

Detection Probabilities ◽

Current Survey

AbstractConsiderable efforts have been invested in recent years to improve methods for both data collection and analyses required for population monitoring. Where historical or current estimates of population size are not adjusted for detection probabilities they may be too inaccurate to provide meaningful estimates of trends and thus monitoring methods need to be adapted. Here, we use data from the Endangered huemul deer Hippocamelus bisulcus to outline a framework to develop accurate robust estimates of detection probabilities that can be incorporated into new surveys in a cost-effective way and applied to existing survey data sets. In particular, by retroactively estimating detection probabilities for surveys of huemul, we show that current survey methods for huemul are inadequate to determine population trends reliably. Based on these results we propose a new monitoring method for the huemul and discuss the importance of estimating accuracies of historical survey data to ensure that changes in the abundance of the species reflect real population trends and are not an artefact of variation over time in the accuracy of survey data.

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