Estimating detection for salt-marsh songbirds during winter using the double-pass rope-drag technique

Area of Science:

• Ecology
• Ornithology
• Conservation Biology

Background:

• Tidal marsh bird species face threats from sea-level rise.
• Winter is a critical period for adult bird survival, yet research often focuses on breeding seasons.
• Understanding winter abundance is crucial for effective conservation of saltmarsh-dependent birds.

Purpose of the Study:

• To assess the effectiveness of the double-pass rope-drag technique for estimating winter abundance of saltmarsh songbirds.
• To determine the optimal number of survey rounds for accurate abundance and detection rate estimations.
• To provide data for conservation strategies addressing sea-level rise impacts on tidal marsh ecosystems.

Main Methods:

• A double-pass rope-drag technique was employed in Virginia tidal marshes from January to March 2014.
• 102 transects (60x250 m) were surveyed to estimate winter abundance of sharp-tailed sparrows, seaside sparrows, and marsh wrens.
• The first pass removed birds; the second pass estimated detection probabilities.

Main Results:

• The double-pass rope-drag technique yielded high detection rates: 98% for sharp-tailed sparrows, 95% for seaside sparrows, and 91% for marsh wrens.
• Estimates were comparable using two survey rounds, though precision decreased.
• Confidence intervals for abundance estimates increased by an average of 14% when using only two of three rounds.

Conclusions:

• The double-pass rope-drag technique is an effective and unbiased method for estimating winter songbird abundance in saltmarsh habitats.
• A minimum of two survey rounds is necessary for reliable estimates.
• Increasing survey rounds enhances the precision of abundance and detection estimates for conservation planning.