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In 2014, we began a project to develop and test non-invasive population monitoring techniques for burrow-nesting seabirds on the Southern Oregon Coast. Whereas populations of surface-nesting seabird can be monitored using aerial photography and visual counts, monitoring of burrow-nesting species is much more challenging, especially on difficult to access offshore islands. Improvement in current techniques along with the integration of new technologies is needed to establish cost-effective and sustainable research and monitoring programs for burrow-nesting seabirds.
The traditional methods for estimating burrow occupancy include "grubbing" (reaching into the burrow) (Kocourek et al. 2009), using a burrow camera, or using audio playback. Cameras are less invasive than grubbing, but depending on species can be less accurate in determining occupancy (Hamilton 2000, Mckechnie et al. 2007). Additionally, relatively small occupancy errors can change population estimates by two or more orders of magnitude since. Mark-recapture estimates can improve population estimates (Sheffield et al. 2006, Sutherland and Dann 2012), but they are much more labor-intensive. All of these techniques require direct monitoring of the contents of each individual burrow. On the Oregon coast, this requires access to steep-sided, rocky offshore islands during the peak breeding season (June/July) when seasonal winds often create hazardous boating conditions. In addition, grubbing at the many plots needed to extrapolate to population estimates is extremely time consuming and causes unintentional harm to birds and burrows.
We are developing methods that are cost-effective and can be used in routine monitoring to track population trends. We simultaneously collected and integrate data from multiple remote sensors of audio, imagery, and radar surveys to calculate abundance indices that were compared to burrow occupancy. The use of remote methods to monitor individual burrows or groups of burrows over the entire season could result in improved measures of abundance and reproductive success while minimizing negative impacts and logistical constraints associated with traditional methods.
Example images from time-lapse trail cameras deployed at storm-petrel colonies in southern Oregon
Orben, RA, AB Fleishman, AL Borker, W Bridgeland, AJ Gladics, J Porquez, P Sanzenbacher, SW Stephensen, R Swift, MW McKown, RM Suryan. 2019. Comparing Automated Photography, Acoustic Recordings, and Radar to Monitor Leach’s Storm-Petrel Colonies. PeerJ 7:e6721 https://doi.org/10.7717/peerj.6721
U.S. Geological Survey - Oregon Cooperative Fish and Wildlife Research Unit
U.S. Fish and Wildlife Service, Region 1 Migratory Birds
U.S. Fish and Wildlife Service, Oregon Coast National Wildlife Refuge Complex
Conservation Metrics, Santa Cruz, CA