A car-based monitoring method reveals new information on bat populations and distributions in Ireland

Abstract

A robust and cost-efficient method for monitoring some of Ireland's more common bat species was devised in 2003 and has been carried out yearly since then. The objective of the scheme is to provide information on bat population trends and distributions in Ireland. Night-time surveys are conducted in July and August, whereby bat vocalizations are recorded from a time expansion bat detector to a minidisc while driving a known route by car at a constant driving speed. Bat vocalizations are subsequently analysed using sound analysis software. In Ireland, the roadside populations of three target species, the common pipistrelle, soprano pipistrelle and Leisler's bat, can be monitored effectively using this car-based method of survey. Power statistics indicate that a decline of high conservation priority of the least frequently encountered species of the three, Leisler's bat, could be detected within 12 years of monitoring if 25, 30 Â 30 km survey squares, each with fifteen 1.6 km transects, are surveyed twice annually. The scheme has revealed new data on the relative bat activity distributions across the island of Ireland. Common pipistrelles are more frequent in the south of the country and Leisler's bats are more frequent in the south and east. Analysis of yearly count data indicated an initially increasing trend in the common pipistrelle and Leisler's bat for the first 4 years of the survey, followed by more recent declines. Ireland has a relatively depauperate bat fauna; hence, a potentially greater number of microchiropteran species could be monitored in other regions using this method. The protocol is easily repeatable and does not have to be carried out by bat specialists. In Ireland, it takes c. 300 h of volunteer time annually to carry out this statistically robust monitoring scheme for all three bat species.

Potential for coupling the monitoring of bush‐crickets with established large‐scale acoustic monitoring of bats

“…For example, using detection distance tables for the Wildlife Acoustics microphone used here at 20 °C and relative humidity of 50% (Agranat ), and given an estimate of how loud each species is (Sound Pressure Level in db), we expect that the detection distance of short‐winged conehead will be about 4 m compared with great green bush‐cricket, which would be detected up to about 24 m. Car transects for Orthoptera monitoring have an advantage that they increase survey coverage and number of contacted individuals, with the potential for estimating abundance, but they have the limitation that conclusions based on the road network can only be made in relation to roadside habitats, which may not be representative of wider wildlife populations (Roche et al . ). One option suggested by Jeliazkova et al .…”

“…In relation to the survey approach of using static detectors left out to record at a location, while this can allow for standardised and representative surveys, there is the limitation that a detector is likely to be sampling a small area, and considering that Orthoptera are relatively immobile, this will produce multiple recordings of the same individual bush-cricket (Jeliazkova et al 2016). For example, using detection distance tables for the Wildlife Acoustics microphone used here at 20°C and relative humidity of 50% (Agranat 2014), and given an estimate of how loud each species is (Sound Pressure Level in db), we expect that the detection distance of short-winged conehead will be about 4 m compared with great green bush-cricket, which would be detected up to about 24 m. Car transects for Orthoptera monitoring have an advantage that they increase survey coverage and number of contacted individuals, with the potential for estimating abundance, but they have the limitation that conclusions based on the road network can only be made in relation to roadside habitats, which may not be representative of wider wildlife populations (Roche et al 2011). One option suggested by Jeliazkova et al (2016), could be to couple road surveys that allow abundance to be estimated with static detectors that allow more representative surveys.…”

Improving geographically extensive acoustic survey designs for modeling species occurrence with imperfect detection and misidentification

“…Challenges associated with traditional capture and visual methods coupled with the increased risk of multiple threats (e.g., Hammerson, Kling, Harkness, Ormes, & Young, 2017;Jones, Jacobs, Kunz, Willig, & Racey, 2009;O'Shea, Cryan, Hayman, Plowright, & Streicker, 2016) have accelerated the widespread use of ARUs for surveying bats. Broad-scale monitoring programs have been initiated across Europe, North America, and elsewhere (e.g., Barlow et al, 2015;Jones et al, 2013;Loeb et al, 2015;Roche et al, 2011;Walters et al, 2012) and rely in part on coordinated acoustic surveys. The complication is that shared echolocation call characteristics from morphologically and ecologically similar bat species can result in incorrect species assignments from automated identification software and misidentification errors for the focal species (Russo, Ancillotto, & Jones, 2017;Russo & Voigt, 2016;Rydell, Nyman, Eklof, Jones, & Russo, 2017).…”

Distribution of Usutu Virus in Germany and Its Effect on Breeding Bird Populations

“…This statistical approach was first developed by Fewster et al ( 31 ) to describe population trends in breeding birds and later successfully used to model bird and bat populations ( 32 , 33 ). We used the GAM framework to fit a single smoothed curve to the trend of the number of bird specimens in the USUV-positive areas and USUV-negative areas per year.…”