Effects of weather, time of day, and survey effort on estimates of species richness in temperate woodlands

ABSTRACT

We used clearly defined measures of weather and time of day to determine their impacts on the number of bird species recorded in 5439 area-search surveys of 142 one-hectare sites in open temperate woodlands. Surveys recording the highest number of species spanned the full range of times of day and weather conditions. For our full dataset, the number of species recorded dropped by 16% at higher wind speeds (>20 km/h), 0.8%/h after sunrise (or 7.4% in the afternoon compared to morning), and 0.5% per degree temperature increase, but was unrelated to cloud cover. Resampling our full dataset, we separated impacts of effort from weather and analysed scenarios which might arise with time or budget constraints. Dawn surveys were less affected by time and weather, and recorded more species than other scenarios per unit of effort, especially at species-rich sites. We demonstrate that setting thresholds for these variables is not warranted if this reduces sample size in a study. Conversely, if researchers are restricted to a fixed number of surveys, then our data highlight that thresholds may be used to optimise results by avoiding periods when less productive conditions, particularly winds >20 km/h, prevail.

KEYWORDS:

• Temperature
• wind
• box woodland
• temperate eucalypt woodland
• survey effort

Acknowledgements

All aspects of this project were worked on by both authors. We thank the following individuals from the Office of Environment and Heritage (OEH): Terry Mazzer and Jenni Garden for undertaking a round of bird surveys each; Michael Bedward for assistance with site selection, data graphing and commenting on an earlier draft of the manuscript, and John Porter for commenting on the manuscript. Reviews of the manuscript by Michael Craig and an anonymous referee provided useful insights for which we are thankful. We thank M. Bedward, L. Rayner, C. Simpson, R. Kingsford, C. Steinfeld, and V. Monamy for their valuable assistance in the field. This work was conducted under a Scientific Licence and an Animal Ethics Permit issued by the NSW OEH.

Supplemental data

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Medical Research Council: [Grant Number xxxx, xxxx].