Brachyramphus marmoratus marmoratus
|Listed||October 1, 1992|
|Description||Small bird with dark plumage above and mottled plumage below.|
|Habitat||Marine environment, but breed inland.|
|Food||Small fish and invertebrates.|
|Reproduction||Nesting March to late-September; clutch of one egg.|
|Threats||Oil spills; gillnet fisheries; forest management practices; logging; nest predation.|
|Range||California, Oregon, Washington|
The marbled murrelet is a member of the Alcidae family whose adult breeding plumage is dark above and heavily mottled below. Wintering adults have a mostly white chest and belly and a lighter colored back. This subspecies is not sexually dimorphic, and the birds measure about 9.75 in (25 cm) long. Juveniles resemble wintering adults but have some mottling on the chest and belly. The bill and tail are dark brown to black.
Brachyramphus marmoratus marmoratus, the North American subspecies, is found in southern Alaska, British Columbia, Washington, Oregon, and central California. Some wintering birds are even found in southern California. Brachyramphus marmoratus perdix, the Asian subspecies, may warrant full specific status on the basis of recent genetic analysis, although status changes for the two subspecies have not yet been recognized.
Marbled murrelets spend most of their non-nesting lives above or in near-shore marine waters no deeper than 260 ft (80 m) where, foraging by pursuit, they dive after and feed on small fish and invertebrates.
Pairs are often seen diving simultaneously, which researchers suggest may increase foraging efficiency. Marbled murrelets also aggregate, loaf, preen, and exhibit wing-stretching behaviors on the water. Marbled murrelets have been found occasionally on rivers and inland lakes.
Marbled murrelets nest inland in Washington, Oregon, and California, typically in large-diameter old-growth trees in low-elevation forests with multi-layered canopies. Marbled murrelets have been observed at some inland sites during all months of the year. Attendance at breeding sites during the non-breeding season may enhance pair bond maintenance, facilitate earlier breeding, or reinforce familiarity with flight paths to breeding sites. Nesting occurs over an extended period from late March to late September. During the breeding period, the female marbled murrelet lays a single egg in a tree containing a suitable nesting platform. Both sexes incubate the egg in alternating 24-hour shifts for approximately 30 days, and the young fledge after an additional 27-40 days. Adults feed chicks at least once a day, and they fly from ocean feeding areas to nest sites at all times of the day, although most often at dusk and dawn. The young are semi-precocial and molt into a distinctive juvenile plumage before leaving the nest. A fledgling's first flight is from the nest directly to the marine environment.
Research into social interactions and nesting patterns for this species indicates that the presence of marbled murrelets in a forest stand may attract other pairs to currently unoccupied habitat within the vicinity. This suggests then that unoccupied habitat in the vicinity of occupied habitat may be more important for recovering the species than suitable habitat isolated from occupied habitat.
This species feeds by diving primarily in near-shore marine waters, usually in water 100 ft (30 m) deep and within 500 ft (152 m) of shore for fish and invertebrates. Some birds have been observed feeding along rivers and on inland lakes.
Adults are probably diurnal for the most part and appear to make feeding flights at dawn and dusk. The chicks may be sensitive to warm temperatures; their activity levels may drop as the temperature increases.
The marbled murrelet spends the majority of the year in the marine environment. They are primarily found inland only during the breeding season but can be observed inland during any month of the year.
This species appears to prefer older forest stands for nesting near the coastline. These sites are characterized by large trees (32 in [81 cm] diameter at chest height), multi-storied stands, and a moderate-to-high canopy closure. The dominant tree species are Douglas fir in Oregon and Washington, and redwoods in California. In some areas, mature stands with old growth components are used. The areas must have trees with large branches or deformities to provide platforms for nests. Nests are generally placed in the oldest trees in the stand. The 16 nests found in California, Oregon, and Washington were all located in old-growth trees with a diameter at chest height of 35-210 in (89-533 cm). Nests are placed high in the tree in areas with good overhead protection.
Stand size is also an important factor. This species was most often found in stands over 500 acres (202 hectares) in California. Concentrations of murrelets at off-shore sites are almost always adjacent to older forests on the coast.
Terrestrial nesting habitat within forest stands and marine foraging habitat used during the breeding season are the two biologically essential components of marbled murrelet habitat. Suitable nesting habitat comprises forested areas with conditions that support nesting; suitable foraging habitat comprises marine areas with conditions that support adequate food supplies.
General habitat attributes are characteristic throughout its range, including the presence of fairly large branches, nesting platforms, adequate canopy cover over the nest, landscape condition, and distance to the marine environment. These characteristics are typically found in old-growth and mature forests, but may be found in younger forests containing remnant large trees. Research through the 1995 nesting season, based on 95 active or previously used marble murrelet tree nests located in North America, found that more than 94% of these nests were in the top half of the nest trees, which may allow easy nest access and provide shelter from potential predators and weather. Canopy cover directly over the nests averaged a high 84%. Nests have been located in forested areas dominated by coastal redwood, Douglas fir, mountain hemlock, Sitka spruce, western hemlock, and western red cedar. Individual nests in Washington, Oregon, and California have been located in Douglas fir, coastal redwood, western hemlock, western red cedar, and Sitka spruce trees.
For nesting habitat to be accessible to marbled murrelets, it must occur close enough to the marine environment for murrelets to fly easily between nesting and foraging areas; 40 mi (64 km) seems about as far inland as the species will normally nest, although distances of up to 52 mi (84 km) have been recorded in Washington.
Terrestrial nesting areas juxtaposed with marine areas that support ample populations of prey species are essential to maintaining successfully reproducing marbled murrelet populations. Nesting murrelets, which must complete at least one foraging round trip per day, have to balance the energetic costs of foraging trips with the benefits for themselves and their young. During years of low prey availability, the distance from nesting areas to adequate foraging areas is probably a critical determinant of reproductive success.
Marbled murrelets spend most of their lives in the marine environment where they consume a diversity of prey species. Murrelets often aggregate near near-shore kelp beds, sand or gravel beaches, and sand banks where suitable prey may concentrate. Near-shore upwellings, waters at the mouths of bays and coastal rivers, eddies in the vicinity of headlands, river mouths and associated plumes, and tidal rips are likely the most important features determining murrelet foraging opportunities. Marbled murrelets generally forage in marine waters at distances of 0.2-1.2 mi (0.3-2 km) from shore; however, they occur at distances up to 14 mi (22 km) from shore in reduced numbers. The murrelet preys on Pacific sandlance, Pacific herring, northern anchovy, osmerids, sea perch, euphausiids, mysids, and amphipods. Fish are an important component of the diet during the summer, which coincides with the nestling and fledgling periods, while euphausiids, mysids, and amphipods seem to be more important in the winter and spring in some areas.
The greatest concentration of murrelets during the nesting season generally corresponds to the largest remaining blocks of suitable forest nesting habitat. A 1996 study found murrelets to be more numerous along Washington's northern outer coast and less abundant along the southern coast, a distribution pattern that appears to be correlated with the proximity of old growth forest, the distribution of rocky shoreline/substrate versus sandy shore-line/substrate, and abundance of kelp. Research in British Columbia found that the highest at-sea murrelet densities in both 1991 and 1993 were seen immediately adjacent to two tracts of old-growth forest, while areas with very low densities of murrelets were adjacent to heavily logged watersheds. In contrast, where nesting habitat is limited in southwest Washington, northwest Oregon, and portions of California, few marbled murrelets are found at sea during the nesting season. Approximately 300 mi (483 km) separate the large breeding populations to the north in Humboldt and Del Norte Counties from the southern breeding population in San Mateo and Santa Cruz Counties. Currently, this reach contains few marbled murrelets during the breeding season; however, the area likely contained significant numbers of marbled murrelets before extensive logging.
Habitat for marbled murrelets has been generally declining since the arrival of European settlers. It is estimated that old-growth forest in Washington, Oregon, and California has declined by two-thirds during the last five decades. Although information specific to the range of the marbled murrelet is not available, habitat for this bird obviously represents a very significant portion of the estimated area once covered by old-growth forests; thus, trends in habitat can be assumed to follow the same general pattern identified for the larger area.
Mature and old-growth forest before the 1800s in western Washington and Oregon is estimated to have been 24-32 million acres (9-13 million hectares), and northwestern California 1.3 to 3.2 million acres (one half to one million hectares). In 1991, there were approximately 70,000 acres (28,000 hectares) of old-growth coastal redwood forest remaining in California.
Marbled murrelets are threatened by impacts to their nesting habitat, marine foraging habitat, and aquatic food supply, as well as direct mortality from human activities such as oil spills and gillnet fisheries. In 1995, it was estimated that marbled murrelets in Washington, Oregon, and California may be declining at a rate of 4-6% per year, which is consistent with the long-term decline from historical populations. These declines may be exacerbated by high mortality rates among birds born the previous year before they reach the ocean for the first time and high mortality rates of juveniles and adults in the marine and terrestrial environments.
The management practices imposed on old-growth forests and other harvested timberlands have left highly fragmented stands of older forests and created large areas of younger forests that have yet to develop habitat characteristics suitable for marbled murrelet nesting. It generally requires 200 or 250 years of natural growth before forests can develop suitable nest trees and nesting habitat for marbled murrelets. This time period may be shorter in redwood and western hemlock forests and in areas where significant remnants of the previous stand remain.
Forest-age distributions have become heavily skewed toward younger even-aged stands as a result of the timber harvest strategies of the last 50-70 years, which have focused on clear-cut logging in many portions of the range of the marbled murrelet. Reduction of the remaining older forest has not been evenly distributed in western Washington, Oregon, and California; rather, timber harvest has been concentrated at lower elevations and in the Coast Ranges, areas generally overlapping the range of the marbled murrelet. Intensively managed forests in Washington, Oregon, and California now have average cutting rotations of 70-120 years, while cutting rotations of 40-50 years are common for some private lands. After forests are clear-cut, the sites are traditionally re-planted with either a single tree species or just a few tree species and then maintained as even-aged stands for maximum wood-fiber production. Site-preparation and management activities may further decrease species diversity. These methods include prescribed burning and the use of herbicides or mechanical methods to control competing vegetation.
Historical logging practices prior to the widespread use of clearcutting techniques consisted of more selective timber harvest that left remnant patches of forests of varying ages with older forest characteristics. The uneven-aged management practices used in these areas usually resulted in more diverse forests, ones that may still contain a modest number of trees that contain suitable marbled murrelet nesting structure. Some of the forests that were affected by past natural disturbances, like forest fires and windthrow, currently provide suitable nesting habitat for marbled murrelets because they retain scattered individuals or clumps of large trees that provide structure for nesting. This is particularly true in coastal Oregon where extensive fires occurred historically. Marbled murrelet nests have been found in remnant old-growth trees in mature forests in Oregon.
Marbled murrelets are believed to be highly vulnerable to predation when on the nesting grounds, and the species has evolved egg and plumage cryptic coloration as a means of foiling detection. Adults also fly to and from nests by indirect routes and often under low-light conditions. Potential nest predators include the common raven, Steller's jay, American crow, gray jay, great horned owl, sharp-shinned hawk, Cooper's hawk, northern goshawk, raccoon, marten, Townsend chipmunk, northern flying squirrel, Douglas squirrel, and fisher. Ravens, Steller's jays, and great horned owls are known predators of eggs or chicks. Adult marbled murrelets in the non-nesting, terrestrial environment have also been preyed upon by sharp-shinned hawks, peregrine falcons, bald eagles, and possibly merlins.
The documented success/failure rates of marbled murrelet nests from 1974 through 1993 revealed that 57% of the 64% of failed nests did so because of predation. It is unlikely that such a high predation rate is both "normal" and one that could be sustained by a stable population of a species. It is quite possible that the predation rate has risen in recent years as a result of increased numbers of predatory jays, crows, and great horned owls in the western United States; habitat changes and food sources provided by humans seem to have spurred growth of their populations. For nests built in shrubs, predators are large mammals such as raccoons and skunks.
Studies of artificial and natural nests conducted in Pacific Northwest forests indicate that predation of forest bird nests may be affected by habitat fragmentation, forest management, and land development. Preliminary results from one study indicate that interior forest nests in contiguous stands far from human activity appear to experience the least predation. Research indicates that the marbled murrelet is one of the most sensitive to forest fragmentation of all Pacific Northwest birds and that general landscape conditions in the form of degree of high-density landscape cover may influence the degree to which marbled murrelets nest in an area. The best available information strongly suggests that marbled murrelet reproductive success may be adversely affected by forest fragmentation associated with certain land management practices.
The major threats to this water bird in the marine environment include oil spills and commercial net fisheries. Unpolluted water is essential for maintaining the health and successful life cycle of individual marbled murrelets and their prey species. Clean water also provides areas for social interactions and other behaviors.
Marbled murrelets have a high vulnerability to oiling, and oil spills have had catastrophic effects when large spills have occurred in the vicinity of murrelet concentrations. Oil spill impacts have been particularly severe in Prince William Sound in Alaska, western Washington, and central California. Oil spills reduce reproductive success, disrupt breeding activity, and affect forage fish populations. Chronic oil pollution can cause mortality through oiling and ingestion of oil. Other forms of pollution may also affect birds directly through toxic effects on their food supply.
The mortality of marbled murrelets from entanglement and drowning in fishing nets has declined in recent years as fishing efforts in coastal fisheries have been greatly reduced because of depressed salmon runs and regulations to reduce mortality have been implemented. Gillnet fisheries are the most significant threat to murrelets in the marine environment in Washington, although closures to specifically protect this taxon were implemented in the 1995 season. Gillnet fisheries still may occur at the mouth of the Columbia River, in Willapa Bay, Grays Harbor, the Strait of Juan de Fuca, and Puget Sound. Oregon no longer has gill net fisheries except for those in the Columbia River. Fishing regulations in California now protect most murrelets from this type of mortality.
It is likely that marbled murrelets, like many other seabirds, are affected by fluctuations in local marine environmental conditions caused by El Niño and other climactic phenomena. In general, increased mortality of adult seabirds and decreased reproductive efforts have been linked with El Niño episodes when food supplies are depressed, although there may be marked differences in effects across regions and among species with different foraging styles. Marbled murrelets are relatively opportunistic foragers, have a great flexibility in prey choice, and can probably respond fairly well to moderate climate-induced changes in prey availability. Seabirds have relatively long life spans, an adaptation which very often allows individuals to reproduce at least once during their lifetime despite adverse conditions. However, the combined effects of habitat loss, over-predation, and repeated El Niño conditions in localized areas over a short time period could cause serious population declines or extirpations.
Conservation and Recovery
Although several different approaches to management of older forests and their associated species have been developed since 1990 through various federal efforts, none of them specifically address marbled murrelet problems or provide a framework for a marbled murrelet management strategy. It was not until July 1993 that a real attempt to concentrate on the marbled murrelet was made; at that time, six of the federal agencies most intimately involved with wildlife and land governance released the Report of the Forest Ecosystem Management Assessment Team. Information from this report was used in what is now referred to as the Northwest Forest Plan. This report and the Northwest Forest Plan finally provide a specific marbled murrelet management strategy for Federal lands.
Within the range of the marbled murrelet, the Northwest Forest Plan designates a system of Late-Successional Reserves, which provides large areas expected to eventually develop into contiguous, unfragmented forest. In addition to Late-Successional Reserves, the Northwest Forest Plan designates a system of Adaptive Management Areas, where efforts focus on matrix areas, where most forest production occurs, and answering management questions. Administratively withdrawn lands, as described in the individual National Forest or Bureau of Land Management land-use plans, are also part of the Northwest Forest Plan.
Specific measures in the Northwest Forest Plan protect all occupied murrelet sites on federal lands outside of the federal reserve system. These measures include surveys prior to activities that may affect habitat and protection of contiguous marbled murrelet nesting and recruitment habitat, defined as stands capable of becoming suitable nesting habitat within 25 years and within 0.5 mi (0.8 km) of areas occupied by murrelets.
The Northwest Forest Plan complements critical habitat designation by stressing the need for protection of large, unfragmented areas of suitable nesting habitat that are well-distributed throughout the entire range of the marbled murrelet.
Concurrently with the implementation of the Northwest Forest Plan, the Marbled Murrelet Recovery Team continues to work on a Recovery Plan that will outline a strategy for recovering the species. The Recovery Plan, which builds on the Northwest Forest Plan, also addresses management needs on non-federal lands and in the marine environment. The maintenance and development of suitable habitat in relatively large contiguous blocks will materially contribute to the recovery of the marbled murrelet. These blocks of habitat should contain the structural features and spatial heterogeneity naturally found at the landscape level, the stand level, and the individual tree level in Pacific Northwest forest ecosystems
The U. S. Fish and Wildlife Service (FWS) published a final rule on listing the marbled murrelet in Washington, Oregon, and California as a threatened species on October 1, 1992, and they originally proposed to designate critical habitat for the marbled murrelet in these three states on January 27, 1994. Based on comments received regarding the original proposal and additional information, the FWS significantly amended its proposed critical habitat designation and published a supplemental proposed rule on August 10, 1995. On February 29, 1996, Judge Barbara J. Rothstein of the U.S. District Court for the Western District of Washington denied a motion to vacate her previous order on completion of the designation of critical habitat and ordered the FWS to complete the final designation by May 15, 1996.
Regional Office of Endangered Species
U. S. Fish and Wildlife Service
Eastside Federal Complex 911
N. E. 11th Ave.
Portland, Oregon 97232
Oregon Fish and Wildlife Office
U. S. Fish and Wildlife Service
2600 S.E. 98th Ave., Suite 100
Portland, Oregon 97266-1398
Telephone: (503) 231-6179
Fax: (503) 231-6195
Ehrlich, P. R., D. S. Dobkin, and D. Wheye. Birds in Jeopardy-the Imperiled and Extinct Birds of the United States and Canada, Including Hawaii and Puerto Rico. Stanford: Stanford University Press, 1992. 259 pp.
U. S. Fish and Wildlife Service. 1 October 1992. "Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for the Washington, Oregon, and California Population of the Marbled Murrelet." Federal Register 57 (191): 45328-45337.
U. S. Fish and Wildlife Service. 24 May 1996. "Final Designation of Critical Habitat for the Marbled Murrelet." Federal Register 61 (102): 26255-26320.
U. S. Fish and Wildlife Service. 1997. Recovery Plan for the Threatened Marbled Murrelet (Brachyramphus marmoratus ) in Washington, Oregon, and California. Portland, Oregon. 203 pp.
"Marbled Murrelet." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (September 19, 2019). https://www.encyclopedia.com/environment/science-magazines/marbled-murrelet
"Marbled Murrelet." Beacham's Guide to the Endangered Species of North America. . Retrieved September 19, 2019 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/marbled-murrelet
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