Behavior of Marbled Murrelets at Nine Nest Sites in Oregon

Abstract

Between 1990 and 1992, 9 active marbled murrelet (Brachyramphus marmoratus) tree nests were found in western Oregon. Incubation was shared equally between adult birds with each bout lasting approximately 24 hr. Incubation exchanges took place during a relatively narrow time period, 30 to 8 min prior to official sunrise, and on average lasted 16 sec. Feedings occurred primarily at dawn, but adults also returned to feed nestlings at dusk and occasionally during mid-day. In contrast to incubation exchanges, the time adults arrived at nests to feed nestlings varied, both within and among nests, and occurred within 104 min and 90 min of official sunrise and sunset, respectively. The duration of feeding visits was also highly variable and ranged from 18 sec to 46 min in length (x = 16.7 min, SE = 1.3). Weather influenced arrival times of adults during incubation and nestling stages; on average birds arrived earlier on clear (' 75% cloud cover) than cloudy (> 75%) mornings. Murrelets at each nest used consistent flight paths when entering and exiting nest trees. Soft vocalizations from adults (groan and whistle calls) and chicks (begging) were heard at all nests during incubation and feeding visits. In contrast, loud calls (keer and groan), which were frequently uttered by adults in flight, were uncommon and detected at only 3 nests. The behaviors observed at murrelet nests were secretive and probably designed to minimize detection by predators. While these behaviors pose challenges for locating nests in forests, knowledge of marbled murrelet activity patterns and behaviors associated with nesting will aid in monitoring efforts and in identifying areas that are used for nesting. The behavior of marbled murrelets (Brachyramphus marmoratus) at nest sites is poorly known. The first marbled murrelet ground and trees nests were not found until 1959 and 1974, respectively (Day et al. 1983, Binford et al. 1975). Locating nests for study has proved difficult because murrelets nest solitarily or in loose aggregations, and are active primarily in low light levels (Sealy and Carter 1984, Eisenhawer and Reimchen 1990, Rodway et al. 1993, Naslund et al. 1995, Nelson and Hamer 1995a). In addition, tree nesting murrelets nest on naturally occurring branch platforms high in the canopies of large, mature conifers (Singer et al. 1991, 1995, Nelson and Hamer 1992, Hamer and Nelson 1995a, Jordan and Hughes 1995, Kerns and Miller 1995, Manley and Kelson 1995, Naslund et al. 1995). The marbled murrelet was recently listed as a threatened species in Washington, Oregon, and California (U. S. 1 Present address: Department of Forest Science, Oregon State University, 020 Forest Sciences Lab, Corvallis, OR 97331-7501, USA. Fish and Wildlife Service 1992) and information on its activity patterns and behaviors at nests is needed to develop monitoring protocols and define future research directions. Prior to 1992, the characteristics of marbled murrelet nests and nesting sites had been documented and described at 10 ground nests in Alaska and 6 tree nests from southcentral Alaska to central California (Binford et al. 1975, Simons 1980, Hirsch et al. 1981, Day et al. 1983, Johnston and Carter 1985, Carter and Sealy 1987b, Quinlan and Hughes 1990, Singer et al. 1991). However, information on the behavior and activity patterns of murrelets at nests was summarized at only 4 of these sites. At 2 ground nests in Alaska, Simons (1980) and Hirsch et al. (1981) described the timing and frequency of feeding visits and measured growth of nestlings. More recent observations of 2 tree nests in central California (Singer et al. 1991, Naslund 1993) provided details on the timing and frequency of nest visits, and descriptions of adults and chicks during feeding bouts at the nest. Additional information on