Marbled murrelets are listed as threatened under the Endangered Species Act. They forage in marine waters but nest in large trees up to 40 miles inland.
The marbled murrelet (Brachyramphus marmoratus) is part of the Alcidae family, which includes other seabirds like murres, puffins, guillemots, auks, and auklets. In North America, murrelets occur along 6,500 miles of coastline from central California to Alaska. They forage in near-shore marine waters for invertebrates and small fish.
Outside of the northern-most portion of their range, murrelets do not build nests. Instead they lay one egg per nesting attempt on large moss-covered limbs in the upper canopy of large trees, which are usually found in mature and old-growth conifer forests. Typically, branches are greater than four inches in diameter and higher than 33 feet above the ground, but murrelets sometimes nest on branches more than 200 feet high.
Most nests have been found within 40 miles of marine waters. Nesting occurs from mid-April to late-September.
Many nests fail due to predation, mainly by crows, ravens, and jays. The first flight of the fledgling must be to marine water. With a relatively high body weight to wing surface area, murrelets tend to fly fast ( more than 40 mph) and straight.
The marbled murrelet was listed as threatened under the Endangered Species Act (ESA) in 1992 by the U.S. Fish and Wildlife Service. It is also listed as threatened by the Washington Department of Fish and Wildlife. Loss of nesting habitat to logging and development is the main threat facing these birds.
There are currently an estimated maximum of 5,000 breeding pairs in Washington State, with roughly 8,000 single birds in the Puget Sound.
Surveys in the Watershed
The Cedar River Watershed (CRW) currently has approximately 14,000 acres of old forest that is potential murrelet nesting habitat. There are also 74,000 acres of second-growth forest that will eventually develop into potential murrelet nesting habitat, as no commercial timber harvest will occur under the CRW Habitat Conservation Plan (HCP).
Before the Habitat Conservation Plan took effect in 2000, there was no systematic effort to assess murrelets in the watershed. One murrelet was detected in the basin in the early 1990s.
In 2005, a three-year study began to determine the status of murrelets in the watershed. First, truck-mounted radar equipment was used to determine the presence of murrelets and to narrow down the location of potential nesting sites. Then audio/visual surveys were conducted in patches of habitat identified from the radar surveys.
From surveys through spring 2007, two sites in the watershed have been identified as “occupied” by murrelets. Since actual nests are very difficult to find, observing behavior typical of nesting birds (such as flying below the tree canopy) is used as a surrogate and is defined as “occupancy.” These sites are approximately 33 miles from marine waters in Puget Sound, where nesting murrelets likely forage.
Future assessments of murrelet nesting will be compared to the results of this study to gauge population trends and murrelet use of maturing second-growth forest.
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Radar and A/V surveys for Marbled Murrelets in the CRW:
- Cedar River Watershed Habitat Conservation Plan: Marbled Murrelet – Measurements of Success
Other bird species in the watershed: