Fledging Behavior, Flight Patterns, and Forest Characteristics at Marbled Murrelet Tree Nests in California

Abstract

We discovered 3 active marbled murrelet (Brachyramphus marmoratus) nests in the same coast redwood (Sequoia sempervirens) tree between 1991 and 1994. The nest tree was in an old-growth redwood-Douglas fir (Pseudotsuga menziesii) forest in Big Basin Redwoods State Park, Santa Cruz County, California. Two of the nests, situated on different branches, were monitored intermittently through fledging in 1991 and 1992. The 1994 nest was in the 1991 nest cup. Eggshell fragments with indications of predation were found under the nest tree in 1993, suggesting that the tree may have been used for at least 4 consecutive years. One fragment encompassed almost two-thirds of a complete egg and is described here. Below-canopy flights were common within the nesting stand, but were concentrated along repeatedly used flight routes. Adults accessed nest sites by flying for at least 100 m through the canopy along these routes. Fledging occurred on 3 July 1991 and on 7 June 1992, 19 and 18 min after sunset, respectively. At fledging, murrelets neither vocalized nor behaved conspicuously. Fledging occurred on the first day in which the nestling had lost all or nearly all of its concealing down. On both occasions, the nestling fledged alone and flew a route not used by the adults. The small (24 cm long) marbled murrelet (Brachyramphus marmoratus) is the only member of the alcid family that nests in trees. It nests on high, large-diameter branches of old-growth trees found in coastal coniferous forests (Hamer and Nelson 1995a). In California, logging of such forests has eliminated most murrelet habitat and reduced population levels such that, in 1992, the species was listed as endangered by the state of California, and as threatened throughout California, Oregon and Washington by the U.S. Fish and Wildlife Service (California Fish and Game Commission 1992, U.S. Fish and Wildlife Service 1992, Nelson and Singer 1994). Through 1994, 65 murrelet tree nests have been found in North America, of which only 22 were active (Nelson and Hamer 1995a). Six of these active nests were from Big Basin Redwoods State Park, Santa Cruz County, California (Binford et al. 1975; Singer et al. 1991, 1992; this study). We conducted field observations of marbled murrelets in Big Basin Redwoods State Park during the breeding seasons of 1991 through 1994. Our primary goal was to observe the fledging of a marbled murrelet from a tree nest, a previously unobserved phenomenon. A secondary goal was to describe behavioral and forest-stand characteristics associated with a successful nest. We report here on the first murrelet nest to be found in a coast redwood (Sequoia sempervirens), the first direct observations of fledging from a tree nest, the first reported re-use of a known successful nest, and the first probable instance of murrelets nesting in the same tree for 4 consecutive years.