Geography 316: Biogeography In progress 12/11/2002
The Biogeography of The Marbled Murrelet (Brachyramphus marmoratus)
by Matthew M. Ward, student in Geography 316
Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD. All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.
Species Name: Brachyramphus marmoratus marmoratus
Species: Brachyramphus marmoratus marmoratus
Description of Species:
The Marbled Murrelet (Brachyramphus marmoratus) is a pacific seabird whose secretive behavior patterns make it a curious organism to study. Marbled Murrelets belong to a family (Alcidae) of birds that are generally characterized by their shorter tails and wings, and often having stocky bodies. The Marbled Murrelet is a plump alcid, generally weighing about 200 grams at maturity. The Marbled Murrelet is a fast flyer and is more comfortable in the air and on sea than on land. The species has poor agility on land, largely due to the fact that its legs and feet are weak and set back on the body. This characteristic doesnt allow for an upright posture, and may also restrict nest selection sites (Gaston & Jones 1998). The summer plumage of the Marbled Murrelet can be described as an extensively mottled blend of dark brown on a background of off-white feathers, with the scapulars fringed white and rufous. In the fall, Marbled Murrelets undergo molting and the winter plumage can be described as more black and white, in that large white scapular patches contrast with the dark upperparts (Gaston & Jones 1998). There is variation among the species and some birds, often young adults and immatures, keep their winter plumage throughout the summer (Small 1994). Both B. marmoratus marmoratus and B. marmoratus perdix have black bills, legs and feet. Murres and puffins are of the same family. Through an exploration of the natural history of the Marbled Murrelet, including its habitat, range and behavior we can understand and appreciate the uniqueness of its niche in its ecosystem. In order to have a better understanding of the Marbled Murrelet it is helpful to explore its binomial nomenclature and gain an understanding of its taxonomic relationships with other organisms. The Marbled Murrelet belongs to the Kingdom Animalia, which includes all animals living or extinct. The Marbled Murrelet is a member of the Phylum Chordata, which includes the vertebrates, tunicates and lancelets. Marbled Murrelets are in the Class Aves, which includes birds both extant and extinct. The Marbled Murrelet is of the Order of Charadriiformes. Charadriiformes are a large order of aquatic birds that feed on sealife, and can be found in inland waters as well as along seacoasts. They are typically diving shore-birds. The Family Alcidae, is a group of web-footed diving seabirds. These birds occur in the northern seas, and include murres, puffins and guillemots. The Marbled Murrelet is of the genus Brachyramphus, and the species has been divided into two races, the North American (Brachyramphus marmoratus marmoratus) and the Asian (B. marmoratus perdix).
The Marbled Murrelet inhabits Pacific coastal areas of North America, throughout the Bering Sea in Alaska to as far south as Central California (Ralph et al. 1995). Populations are larger and more frequent at the northern boundaries of its range, with populations becoming more fragmented and disjunct towards the southern boundaries. The marbled murrelet nests almost exclusively in old-growth forests, and so its presence in a given place is dictated by the presence of old-growth forests. The Brachyramphus species are atypical from all other Alcids in that they breed on land in isolated old-growth coniferous forests. Most Alcids breed on the ground colonially on islands or outcrops that are free from predators. On land, the Marbled Murrelet nests exclusively in the upper canopy of successional and old-growth forests, primarily Douglas Fir (Psuedotsuga menziesii). It is believed that this unique land-breeding adaptation occurred during the mid- Miocene when giant redwood trees (Metasequoia glyptostroboides) covered the coast from the Aleutians and Alaska throughout California. (Ralph et al.1995). Marbled Murrelet nests are located atop a moss or detritus-covered depression in a large diameter horizontal branch, towards the tops of fully developed trees. Most nests are found 70-80 % of the way up the tree, and often have at least 75% of total coverage from the top, allowing nest sites to be virtually invisible from a terrestrial as well as aerial standpoint (Hamer & Nelson 1995).
Typically, Marbled Murrelet nests are found inland, within 10 km from the coast, while in Alaska, nests may be as close as 1km from the coastline (Hamer 1995). We must consider that Marbled Murrelet distributions appear to be limited by the availability of appropriate habitat (e.g. old growth coniferous forests), and nesting can occur as far as 70 km inland. The loss of Marbled Murrelet habitat through logging and human interests has adversely affected populations and frequencies of distributions, particularly along the Pacific Coast in Washington, Oregon, and California where old-growth forests have been exploited for their resources.
In consideration of their secretive behavior on land, the Marbled Murrelet is more easily studied at sea, for this is where it spends much of its time. The species may forage up to 70 km one way daily in pursuit of food (Gaston & Jones 1998). The majority of Marbled Murrelet studies have been conducted at sea, and a fair amount is known regarding feeding and mating habits. The species is largely crepuscular, with most inland activity occurring an hour before and after sunrise (Naslund & ODonnell 1995). Thanks to the upwelling of cold, nutrient-rich water along the Pacific Coast, the Marbled Murrelet spends most of its time foraging in these organism rich waters. The Marbled Murrelet typically feeds in nearshore waters such as fiords or bays, or at tide rips between islands. In the summer, small fish such as sandlance (Ammodytes hexapterus), the northern anchovy (Engraulis mordax) and herring (Clupea harengus) are tasty prey for Brachyramphus. In the winter, similar to other Alcids, the species tends to consume a greater proportion of invertebrates (Gaston & Jones 1998). While feeding, Brachyramphus will dive and drive up a school of fish and then use shallow dives to keep the fish at the surface, picking them from the water, one at a time. The feeding frenzy often attracts other seabirds such as gulls and murres.
Socially, Marbled Murrelets are non-colonial, rather they travel as monogamous pairs that nest in remote locales. They are known to gather at sea into signifigant flocks that may contain substantial portions of the population (Strachan 1995). Courting occurs at sea, with distinctive body postures. The courting pairs generally perform a bill-up display while swimming side by side, and are accompanied by soft nasal calls (Nelson & Hamer 1995). Egg-laying takes place in between March and July along the Pacific Coast, and 24 hour incubation shifts are equally shared between mates. Chick rearing lasts all year until early September in all parts of North America (Hamer & Nelson 1995).
In the past decade there has been an explosion of studies regarding Brachyramphus marmoratus. With regards to the sensitive habitat required for successful breeding of the species (e.g. old-growth forests), the bird has become a source of controversy among opposing interests that include environmentalists against logging and urbanization machines. The Marbled Murrelet is listed as a threatened species under the Endangered Species Act in both the United States and Canada. Logging is particularly destructive to the nesting habitat of Brachyramphus marmoratus. Those wide, horizontal branches necessary for nests are simply not large enough and well established in second-growth forests to support Brachyramphus. According to Ralph (1995), All murrelet nests, south of Alaska, have been found in old-growth trees (>81 cm d.b.h.), therefore all nests have been in stands with old-growth trees. Another issue with even minor logging in a Marbled Murrelet habitat is the increased rate of predation due to loss of canopy cover. Without the thick canopy cover that makes nests virtually invisible to aerial predators, eggs and young are more imperiled. Predators of Marbled Murrelet nests include Common Ravens (Corvus corax) and Stellers Jays (Cyanocitta stelleri). The presence of humans often alters the natural behavior of birds such as the Marbled Murrelet, who nests and forages in uninhabited areas. Human activity will startle a nesting parent who will take flight, consequently leaving eggs or hatchlings increasingly vulnerable to predation (Knight & Gutzweiller 1995). Marbled Murrelet populations have been on the decrease in recent years (Ralph et al. 1995). While populations are substantial in Alaska and Canada, there is a direct connection with the loss of habitat and lower population rates in Washington, Oregon, and California (Ralph et al. 1995). The Marbled Murrelet is a unique species with particular needs, whose population counts serve as a barometer for the state of affairs of the environment it lives in. Through education about the preservation and value of these natural resources, we as a community can become better stewards of the world we live in.
The evolution of the Marbled Murrlelet is a fascinating exploration of its phylogeny and development throughout the ages. While new data are constantly being added to existing science on the topic, it is believed that birds (Aves) first evolved from theropod dinosaurs during the Jurassic Period some 150 million years ago (Chiappe 1995). Evidence comes from fossil remains of Archaeopterix lithographica from the Solnhofen Limestones in Germany. The Solnhofen Limestones preserved fossils well due to their carbonate composition and flat-pane cleaving properties. Also, marine sediments tend to have a gentle depositional process, which gently entomb and preserve specimens. It was through this high quality fossilization that scientists discovered Archaeopterix had feathers. It is debated whether the feathers were used for flight, thermoregulation, or a combination of both. While the tails of modern birds contain only feathers, Archaeopterix lithographica had a muscular and ligamented tail, as well as a scaled snout with teeth, rather than a beak. It is these traits, as well as other skeletal characteristics, that point to Archaeopterixs dinosaur heritage.
Living birds are classified in the taxon Neornithes, and are further divided into two groups based on palate physiology, Paleognathae and Neognathae (Chiappe 1995). First appearing in the Late Cretaceous some 70 million years ago, neognath birds include penguins and sea diving birds such albatross, as well as high energy hummingbirds. It is in this taxon that we find the phylogeny of the alcids and Brachyramphus marmoratus. While there is scientific debate regarding when exactly alcids began appearing in the fossil record, the first unequivocal record of alcid fossils are from the middle Miocene, approximately 15 million years ago (Gaston & Jones 1998). Considering that marine sediments preserve fossils well, and alcids are marine birds, scientists are benefited with a fairly good fossil record of the family. At this point it seems appropriate to briefly discuss some common evolutionary traits of the auks, or family alcidae (auk is the English equivalent to Alcidae and in literature, Auk and Alcid may be used interchangeably). Alcids share a compact, streamlined body, short wings and a short tail. All alcids have 11 primary wing feathers, the outermost being non-functional and small and longest one is typically the tenth. Secondary feathers vary from 16 to 21 (Gaston & Jones 1998). Alcids fly with rapid wing-beats and do not soar or glide, rather they use the spread feet for steering or braking. Alcids are specially adapted for underwater swimming and this is evident in various technical skeletal characteristics (Gaston & Jones 1998).
By the late Pliocene (2-3 million years ago) two species of Brachyramphus shared the California seabird community with five other species of alcids (Gaston & Jones 1998). The adaptation of Brachyramphus marmoratus to nest primarily in old-growth forests probably occurred in the mid Miocene (26 million years ago) when large dawn Redwoods (Metasequoia glyptostroboides) blanketed the North American Pacific coastline form Southern California to the Aleutian Islands (Ralph et al. 1995). The initial divergence between Brachyramphus marmoratus marmoratus and its closest relative, Brachyramphus marmoratus perdix (the asian variety) likely occurred during the mid Pliocene, approximately 3 million years ago. It was during this time that temperatures cooled, and eliminated old-growth forests in the exposed Aleutian Islands. It is likely that this climatological change led to a gap in east-west distributions of murrelets and isolated breeding stocks (Ralph et al. 1995).
At the northern end of its range, the distribution of the Marbled Murrelet is continuous off the coast of SE Alaska, Prince William Sound, Kenai Peninsula, throughout the Aleutians, and off the coast of Vancouver Island where there are sizeable stands of old-growth forest (Gaston & Jones 1998). It is estimated that there are 200,000 or more individuals in Alaska (Ralph et al. 1995). Population distributions become more disjunct and less frequent throughout Washington, Oregon, and California. This is largely due to the loss of old-growth forest to development and timber industries throughout the marbled murrelets range. It is estimated that populations in Washington may exceed 5,500 and in Oregon there may be 5,000-15, 000 individuals. In California individuals are estimated at 6,450 (Ralph et al. 1995).
Marbled Murrelets nest in old-growth forests, and at the northernmost tips of its range, they have been known to have ground nests on remote, predator-free islands and rocky outcrops (Gaston &Jones 1998). On land, nests are found inland, typically within 10 km of the coast and can be as close as 1 km from the ocean (Hamer 1995). Due to their fragmented habitat, marbled murrelets have been known to travel as far as 70 km inland to nest. On land, Marbled Murrelet nests are located atop large moss and detritus covered depressions in a horizontal branch (Hamer & Nelson 1995). These platforms result from natural deformations and heavy moss and epiphyte growth atop exceptionally large limbs of old growth successional trees (Gaston &Jones 1998). Nests are most frequently found in Douglas fir (Pseudotsuga menzeisii), Sitka spruce (Picea sitchensis), mountain hemlock (Tsuga mertensiana), and coastal redwood (Sequoia sempervirens) (Hamer & Nelson 1995). These old, mature, large horizontal branches that are necessary for nest sites are not present in second growth forests. All murrelet nests found south of Alaska, have been in old-growth trees (> 81 cm d.b.h) exclusively (Ralph et al 1995).
Map of Distribution:
Other interesting issues:
The impact of human encroachment into Marbled Murrelet habitats has greatly limited its distribution along the Pacific Coast. Logging and development have taken the greatest toll. While mammalian predation on the Marbled Murrelet is limited, largely due to their remote nest sites, increased predation by aerial predators is attributed to the loss of canopy cover where even small-scale logging practices are conducted. Marbled Murrelets are also vulnerable to pollution and oil spill events. It is estimated that 8,400 were killed by the Exxon Valdez oil spill (Piatt & Lensink 1989). Marbled Murrelet populations have been on the decrease in recent years (Ralph et al. 1995). While populations are substantial in Alaska and Canada, there is a direct connection with the loss of habitat and lower population rates in Washington, Oregon, and California (Ralph et al. 1995). The Marbled Murrelet is a unique species with particular needs, whose population counts serve as a barometer for the state of affairs of the environment it lives in. Through education about the preservation and value of these natural resources, we as a community can become better stewards of the world we live in.
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[September 27, 2002]
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