HAMER, T.E., SCHUSTER, S.M. & MEEKINS, D. 2005. Radar as a tool for monitoring Xantus’s Murrelet populations. Marine Ornithology 33: 139-146.

Xantus’s Murrelets Synthliboramphus hypoleucus are vulnerable to extirpation from breeding islands through high mortality rates from introduced mammalian predators. Black Rats Rattus rattus were eradicated from Anacapa Island in 2001 and 2002 to restore seabird populations. For baseline and subsequent monitoring to assess the results of the rat eradication on Xantus’s Murrelet populations, we developed population monitoring methods using a modified marine radar system and conducted nocturnal surveys to count the numbers of birds flying into or out of sample nesting habitats during the 2000 breeding season. High activity periods, activity zones, and specific behaviors were examined for their ability to generate reliable data for a long-term population monitoring program. Radar is a useful tool to quantify the level of breeding activity in sample areas at nesting colonies and can be used to monitor population changes, compare relative sizes of different colonies, locate new breeding colonies, confirm the continued existence of known historical colonies, and document use of specific nesting habitats at colonies.

Key words: California Channel Islands, introduced predators, radar, monitoring, rat eradication, Synthliboramphus hypoleucus, Xantus’s Murrelets