Final Report: 2004 Snowy Plover Breeding in Coastal Northern California (original) (raw)

For the fourth consecutive year, biologists from Humboldt State University and Mad River Biologists monitored and managed the Snowy Plover (Charadrius alexandrinus nivosus), a federally listed species which breeds in coastal, northern California (Recovery Unit 2). Bimonthly surveys showed that most (64) breeding plovers occurred in Humboldt County whereas fewer plovers bred in Mendocino (10) and Del Norte (0) counties. For the first time in over two decades, plovers nested at Gold Bluffs Beach, Humboldt County where they fledged at least one chick. Overall, we observed 74 breeding adult plovers in Recovery Unit 2, with most in Humboldt County. As an estimate of the local breeding population, this number is slightly higher than the past three years when 51-63 plovers bred locally, although this increase stemmed mostly from 10 plovers that nested in Mendocino County. Most (64%) breeding plovers were individuals that had returned from 2003, including 7 locally marked chicks (11% of 61 chicks marked locally in 2003) and 35 older adults (19 males and 16 females). The number of marked (banded elsewhere along the Pacific coast) and unmarked immigrants (newly banded) increased markedly compared to 2003 and 2002. Emigrants from Recovery Unit 2 nested at several locations along the Pacific coast. For the first time in four years, more (62%) plovers bred on beaches than gravel bars of the Eel River. Plovers initiated more nests along ocean beaches (45) than gravel bars (25), probably because clutches survived poorly on beaches resulting in more replacement clutches. Overall, apparent nest success (number of nests hatching at least 1 chick) was higher (43%) than the past two years (37% in 2002 and 40% in 2003) but lower than 2001 (68%). Nest success was lower at Clam Beach (31%), where we erected predator exclosures at 60% of nests (21/35), than on gravel bars of the Eel River (48%; no nests exclosed). We suspect mammals and corvids consumed most depredated nests on beaches. We recorded three cases of a nest and/or exclosure being vandalized by humans, which r esulted in the failure of two clutches. In total, 76 chicks hatched and 39 fledged (survived 28 days). On beaches, 43% of 46 chicks successfully fledged whereas 60% of 30 chicks fledged on gravel bars. On Clam Beach, where we used symbolic fencing from 23 April to 14 September to manage human intrusion into plover breeding habitat, three of four nests hatched 8 chicks of which 4 survived to fledge; these surviving chicks remained within the area of symbolic fencing for nearly all of the 28 day chick-rearing period. Similar to previous years, most (81%) plover chicks that died succumbed in the first 10 days of life. In 2004, the percentage of chicks that successfully fledged and chick survival rates were higher than estimates recorded for the past two years, but they remain lower than estimates for 2001. In 2004, males breeding in Recovery Unit 2 fledged 1.2+1.1 chicks. However, over the past four years, male plovers that nested on gravel bars fledged significantly more chicks (1.5+1.4 than those breeding on o cean beaches (0.8+1.0). Based on these findings, we recommend that management of plovers in Recovery Unit 2 include: 1) continued use of predator exclosures to protect clutches on beaches; 2) greater protection of important nesting and brood rearing sites in areas of high human use using symbolic fencing, especially during periods when young chicks are present; 3) limitations on vehicle access to plover breeding habitats; and 4) improved management of high quality breeding habitat along the gravel bars, especially the county-owned site, to reduce human impacts.