Using an unoccupied aerial vehicle to study Clapper Rail demography in the salt marshes of coastal Delaware, USA
Date
2023
Authors
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Publisher
University of Delaware
Abstract
Unoccupied Aerial Vehicles (UAVs) provide novel methods to study wildlife in a potentially more efficient manner than traditional methods. UAV methods can be particularly useful for studying secretive marsh birds, as marsh accessibility varies greatly, and UAVs can provide access to otherwise inaccessible areas. I used a UAV equipped with a thermal imaging camera to search for Clapper Rail (Rallus crepitans) and other tidal marsh birds nesting in salt marshes on the Delaware coast, USA in 2021 - 2022. I conducted traditional ground-based systematic nest searches with a field crew at two intensive sites with different levels of accessibility. I piloted the UAV equipped with a thermal imaging camera over the same two sites and compared the number of nests detected between ground surveys and the thermal camera deployed on the UAV. I completed thermal imaging flights before sunrise for the greatest thermal contrast between the nests and the marsh vegetation. I ground-truthed suspected nest points after each flight to confirm that the point was a nest and determine which marsh bird species each nest belonged to, as distinguishing species from the thermal imaging alone is difficult. I found that the UAV detected fewer Clapper Rail nests than ground surveys in the accessible sites (17 and 28 nests respectively) and the UAV detected more Clapper Rail nests than the ground surveys where access was low (16 and 5 nests respectively). I also detected nests of tidal marsh passerines like Seaside Sparrow (Ammospiza maritima), Marsh Wren (Cistothorus palustris), and Red-winged Blackbird (Agelaius phoeniceus), indicating that thermal imaging flights with UAVs could be used to document smaller species breeding in tidal marshes. Using data collected in 2021 and 2022, I compared the efficiency of each method of finding marsh bird nests (ground surveys vs UAV) to determine method efficiency. I found that the UAV covered more area than the systematic nest searches, but on average took more time than the systematic nest searches. I also conducted photogrammetric surveys of the vegetation at all study sites to gain insight into the marsh vegetation characteristics at and around Clapper Rail nests. I compared these characteristics at nest points and random points to determine if a difference could be detected. I found that Clapper Rail nest sites contained 60% more low marsh, 40% less high marsh, and 20% less upland than the random points. Given the current conservation challenge associated with maintaining tidal marsh breeding birds during rapid increases in sea-levels, a non-invasive and rapid survey method that can efficiently document and quantify breeding and vegetation characteristics can aid in prioritizing marshes for conservation, management, or restoration.
Description
Keywords
Unoccupied aerial vehicles, Breeding birds, Birds nesting, Thermal imaging