Ancient murrelet (Synthliboramphus antiquus) COSEWIC assessment and status report: chapter 7
Habitat
Ancient Murrelets live mainly in subarctic waters where mean annual surface water temperatures are between 5 and 15 °C (Kitano 1981). They breed on islands between 20 and 2000 ha in area (Gaston 1994b). Breeding sites are situated inland from the sea up to 300 m, rarely to 400 m (Rodway et al. 1988; Rodway 1990; Rodway 1994). This species does not coexist naturally with any terrestrial mammalian predators except river otters, Lutra canadensis (Gaston 1992).
In the Queen Charlotte Islands, SE Alaska, the Peter the Great Bay, and probably also in the Kuril Islands, Ancient Murrelets nest under forest canopy. Burrows are tunneled under the base of trees, stumps, or fallen logs (Gaston 1992) and may penetrate fissures in the underlying rocks (Drent and Guiguet 1961). On Frederick Island 79% of the burrows are under western hemlock (Tsuga heterophylla) (Vermeer et al. 1984). However, from Kamchatka through the Commander and Aleutian islands, and as far east as the Gulf of Alaska, Ancient Murrelet colonies are found on treeless islands (Gaston 1992). Where forest is available, it appears to be the species’ preferred breeding habitat (Vermeer et al. 1984). Where it is absent, Ancient Murrelets usually pick the most densely vegetated area available. There may be many reasons for the choice of this habitat type, including stability of the soil for digging and this may be more significant than vegetative cover (Nettleship 2004 pers. comm.). On Buldir Island, in the Aleutian Islands they occupy the lowland tall-plant complex that grows to about 1 m high (Byrd and Day 1986). In the eastern Aleutians, the birds are found in Elymus/ Calamagrostis grassland and mixed Elymus and Umbelliferae. Burrows are also found in the foundations of abandoned native houses (Nysewander et al. 1982). Tussock grasslands are probably the birds main breeding habitat through much of their Alaskan range (Bendire 1895; Nysewander et al. 1982), but they also breed on small islands practically devoid of vegetation, and where they occupy rock crevices; the use of scree on islands off the Alaska Peninsula is common (Gaston 1994b).
There is no evidence that the Ancient Murrelet population is limited by the availability of breeding habitat, except at a few colonies where burrow density is high and all suitable habitat is occupied. In the Queen Charlotte Islands, they inhabit all but the largest islands of the archipelago because all but a few very small and exposed islets support coastal rainforest, their preferred habitat. Burrow density at colonies varies from high to low with some areas vacant that appear suitable for nesting (Rodway et al. 1988; Gaston, pers. obs.). Burrowing density decreases from south to north along the islands of southeast Moresby. Almost half the plots from colonies in the Queen Charlotte Islands had burrow densities below 0.33/m2 (G.W. Kaiser, unpublished data, in Harfenist 2003). Expansion of the colony on Langara after the removal of rats indicates that predators may limit population size at certain colonies (Drever 2002). Competition with Cassin’s Auklets may occur in a few places where the species breeding habitats overlap (Vermeer et al. 1984) but is probably not an important limiting factor (A. Gaston, pers. comm.).
Habitat loss is a continual threat for most Ancient Murrelet colonies despite existing federal and provincial protection, including the recently created Wildlife Habitat Areas (see next section). The extent of the negative impact that human disturbance can have is seen in the case of a colony on southern Langara Island that appeared to be displaced when a fishing lodge was built (Vermeer et al. 1997). Though an extreme example, these birds are at risk from any visitor activity that damages burrows or destroys their habitat (Harfenist et al. 2002).
Sixteen of 31 Ancient Murrelet nesting colonies are protected under the Canada National Park Act in the Gwaii Haanas National Park Reserve, the southern part of the Queen Charlotte Islands (Fig. 3). One large colony off the west coast of Graham Island, Hippa Island, is a Provincial Ecological Reserve. Two other colonies, Reef Island and the Limestone islands, are protected as Wildlife Management Areas under the BC Wildlife Act. Two colonies (Lucy and Cox islands), where rats eradicated Ancient Murrelets, are on provincial crown land (Harfenist et al. 2002).
Under the Identified Wildlife Management Strategy (IWMS) of the BC Forest and Range Practice Act (formerly the BC Forest Practices Code), 11 Wildlife Habitat Areas have been approved for the protection Ancient Murrelet breeding colonies. These include Frederick, Helgesen, Marble, Luxmoore, Rogers, Sauders, Instructor, Lihou and Willie Islands (A. Hetherington, 2003, pers. comm.; info available http://wlapwww.gov.bc.ca/wld/identified/wha_areas.htm). Wildlife Habitat Areas designate important habitats in which activities are managed to limit their impact on the Identified Wildlife element for which the area was established.
Presently, there are no plans under the Canada Wildlife Act to create National Wildlife Areas in the Queen Charlotte Islands. However, there are 14 proposed ‘Haida Protected Areas” of which the largest is Duu Guusd (Langara Island) (Harfenist et al. 2002).
Figure 3: Location of Haida and Federal Protected Terrestrial Areas as Well as Provincial Parks, Ecological Reserves and Wildlife Management Areas in Queen Charlotte Islands
Harfenist et al. 2002.
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