Movements of radio-marked California Ridgway's rails during monitoring surveys: Implications for population monitoring

Journal of Fish and Wildlife Management
By: , and 

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Abstract

The California Ridgway's rail Rallus obsoletus obsoletus (hereafter California rail) is a secretive marsh bird endemic to tidal marshes in the San Francisco Bay (hereafter bay) of California. The California rail has undergone significant range contraction and population declines due to a variety of factors, including predation and the degradation and loss of habitat. Call-count surveys, which include call playbacks, based on the standardized North American marsh bird monitoring protocol have been conducted throughout the bay since 2005 to monitor population size and distribution of the California rail. However, call-count surveys are difficult to evaluate for efficacy or accuracy. To measure the accuracy of call-count surveys and investigate whether radio-marked California rails moved in response to call-count surveys, we compared locations of radio-marked California rails collected at frequent intervals (15 min) to California rail detections recorded during call-count surveys conducted over the same time periods. Overall, 60% of radio-marked California rails within 200 m of observers were not detected during call-count surveys. Movements of radio-marked California rails showed no directional bias (P = 0.92) irrespective of whether or not playbacks of five marsh bird species (including the California rail) were broadcast from listening stations. Our findings suggest that playbacks of rail vocalizations do not consistently influence California rail movements during surveys. However, call-count surveys may underestimate California rail presence; therefore, caution should be used when relating raw numbers of call-count detections to population abundance.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Movements of radio-marked California Ridgway's rails during monitoring surveys: Implications for population monitoring
Series title Journal of Fish and Wildlife Management
DOI 10.3996/092014-JFWM-069
Volume 6
Issue 1
Year Published 2015
Language English
Publisher U.S. Fish and Wildlife Service
Publisher location Washington, D.C.
Contributing office(s) Western Ecological Research Center, San Francisco Bay-Delta
Description 11 p.
First page 227
Last page 237
Online Only (Y/N) N
Additional Online Files (Y/N) N