Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2017, with a known 29 active nesting sites providing data, a decrease of 5 active nesting sites from 2016. An estimated 4097-5598 tern breeding pairs established 5983 nests and produced 1131-1655 fledglings across California. The fledgling to breeding pair ratio was 0.2 to 0.4. Statewide, 9518 eggs were reported, with an average clutch size of 1.72 eggs. Camp Pendleton, Naval Base Coronado, Batiquitos, Point Mugu, Huntington, and Alameda Point each had over 300 minimum nests (same sites with > 300 nests in 2016), which represented 75% of the state nest total, and produced 65% of the state’s fledglings. Overall least tern mortality (combined life stages of egg, chick, fledgling, and adult) due to non-predation factors was greater than mortality due to predation in 2017. However, predation mortality for eggs and adults was greater than non-predation mortality. Of the non-predation egg mortality events, the highest cause of failure was attributed to abandonment prior to the expected hatching date and post-term. With the expressed consent of Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) and Terra Peninsular we are able to report California least tern breeding data for the first time on the Baja peninsula. For 2017, a total of 472 pairs were reported from Ensenada to as far south as La Paz. These surveys were conducted by a team of researchers that visited 27 of the known 31 nesting sites during the breeding season. Least terns were also observed in the State of Hawaii on the Island of Hawai'i in 2017. Monitors reported the presence four pairs producing six fledglings at Kohana'iki on the leeward side of the island, with the nesting season occurring from April through July (Baird et al. 2017). These species were confirmed to be least terns by genetic analysis and have been observed nesting on the Island of Hawai'i since 2012 (Scott Waddington, pers. comm., 2012, Baird et al. 2014).