Urban flyways survey on bat commuting along movement corridors

Bennett, Victoria1

Published Aug 12, 2024 on Dryad. https://doi.org/10.5061/dryad.bnzs7h4kh

Data files

Aug 12, 2024 version files 26.02 KB

Abstract

Urbanization can hinder movement and restrict landscape permeability for wildlife. However, there is the potential to improve landscape connectivity by establishing and maintaining movement corridors throughout urban areas. One way to achieve this is through the urban forest; the collection of trees in an urban area. Specifically, it is the characteristics of trees within this forest that can provide the structural and functional connectivity that enables wildlife to move effectively through urban areas. To investigate this, we explored the influence of four tree characteristics, alone and in combination, on bat commuting activity along 30 potential movement corridors in an urban setting in north central Texas. Along 10, 30, and 50 m corridor sections, we calculated percent canopy cover, and maximum gap distance between canopies, and canopy rugosity using a 60 cm resolution tree canopy layer, while maximum tree height was determined in situ. We then conducted behavioral observations using thermal cameras and acoustic monitoring along the 10 m section of each site between March and September of 2022 and 2023 to determine the amount of time bats were observed commuting/hr and species present. Our analysis revealed that increasing percent canopy cover and rugosity positively influenced commuting activity up to a certain threshold (>60% and >1.3 respectively), beyond which they may became detrimental. In contrast, the presence of gaps in the canopy lowered commuting, while tree heights >11 m increased this activity. When considered together, bats in our study area showed a preference for commuting routes with tall trees and straighter, less cluttered canopies with no gaps. Additionally, sites with these features had a greater species diversity. These findings suggest that we can manage and plan the urban forest by establishing an interconnecting network of tree-lines and forest edges to enhance landscape permeability for bats and subsequently aid urban bat conservation.

README: Urban Flyways Survey Data

https://doi.org/10.5061/dryad.bnzs7h4kh

Description of the data and file structure

The data is divided into two worksheets, Behavioral Observation Data and Site Metrics.

For the behavioral observations, we used two thermal cameras to record bat activity at linear features. One camera pointing parallel to that feature, while a second camera was positioned perpendicular to the linear feature. From the footage recorded in 1 hour surveys, we used video analysis software to view the camera footage from both cameras side-by-side and record the instances when bats were observed commuting in the field-of-view. We then summed the amount of time bats were observed commuting in the field-of-view for each 1-hr survey. We also conducted acoustic monitoring during the behavioral observation surveys to discern the number of species present. For this, we placed the detector parallel to the center of the linear feature with its microphone angled upwards. We used bat call analysis software to manually identify bat echolocation calls to species (where possible), from which we determined the number of species that were recorded in the 1-hr surveys at each site.

For site metrics, at each of the 30 study sites we recorded percent canopy cover, maximum gap distance, maximum tree height, and rugosity along a 50 m section of each linear feature selected, as well as 10 m and 30 m lengths extending from the center of the survey site. For canopy cover, we calculated the percentage of area covered by the canopies of trees present within 10 m by 10 m, 30 m by 10 m, and 50 m by 10 m section from satellite imagery. For gap distance, we measured the distance from the edge of every tree canopy present (if >0 m) to its nearest neighbor and determined the maximum distance for each section at each site. For maximum tree height (m), we measured all trees in each section at each site using a range finder. Finally, for rugosity we determined the ratio between the length of tree canopy edge and an equivalent straight line (i.e., rugosity index) for each section at each site.

Files and variables

File: Urban_Flyways_Survey_Data_Final.xlsx

Description: The data is divided into two worksheets, Behavioral Observation Data and Site Metrics.

Variables for Behavioral Observation Data

amount of time bats were observed commuting in the field-of-view for each 1-hr survey.
number of species that were recorded in the 1-hr surveys at each site.