MURRELET RESEARCH AND POPULATION ESTIMATES
The Marbled Murrelet is a secretive bird and little was known about its population size or biology in B.C. prior to the 1990s. Since the publication of the 1994 Marbled Murrelet Recovery Plan there has been considerable effort directed towards Marbled Murrelet research in British Columbia. A key role for the Recovery Team is to evaluate the science and thus provide advice to decision-makers regarding conservation and management strategies. Some current research topics and findings are included below in the population estimates and research sections. A detailed scientific review of Marbled Murrelet research within B.C. is available as a Canadian Wildlife Service Technical Report.
Estimating the number of Marbled Murrelets in B.C. has been difficult because, unlike most other seabirds, Marbled Murrelets do not nest in a few large colonies. Instead, the birds nest solitarily over much of the B.C. coast and do not congregate in large numbers at any time of year. Marbled Murrelets are currently estimated to number roughly 55,000 to 78,000 in British Columbia. That population estimate is based on radar surveys and at-sea surveys. Inventory methods have been standardized by the Resources Information Standards Committee (formerly Resources Inventory Committee) and are available on-line. Survey methods are outlined below:
Marbled Murrelet nests are very difficult to find. The first nest was not found in B.C. until 1990. Researchers have now found about 200 Marbled Murrelet nests, more than half of which are in British Columbia. Most nests in B.C. have been found on large, moss-covered branches (15-75 cm diameter) of large, old-growth conifer trees. A couple of nests have been found on cliff ledges and one has been found in a deciduous tree. Marbled Murrelets are poor fliers who do not build nests. They fly into an opening in a forest canopy and stall-land on a wide, mossy bough with overhead foliage that provides cover. The bough must be high enough for them to jump off and start flying from a free-fall.
Nests or nesting areas have been found by surveying areas of forest suspected to have nesting birds. Several different survey methods have been used including:
Radio Telemetry has also been used to track Marbled Murrelets to nesting locations. Birds are captured at sea at night using a bright light and dip-net. A small transmitter that emits radio waves at a preset frequency is attached to birds caught at sea. Each transmitter emits radio waves at a separate frequency which allows the identification of individual birds. Researchers use a helicopter and a radio receiver to determine the direction from which the signal is strongest. Once the general area of the nest is located, a ground crew is deployed to help pin point the actual nesting tree. Telemetry has been successfully used to locate nests in Desolation Sound, Clayoquot Sound and in Mussel Inlet. (More information about this project can be found at the Centre for Wildlife Ecology website.)
Field data on nest site characteristics have been used to develop models that facilitate the prediction of suitable nesting habitat for Marbled Murrelets based on information obtained from habitat maps. There are several models for murrelet nesting habitat evaluation currently under development for different parts of the coast in British Columbia.
(Note that the Pacific Seabird Group established a Marbled Murrelet Technical Committee in 1986 to assemble researchers and other interested parties to integrate research objectives and methods, and share information on the biology of murrelets).
In order to understand why a population of animals is increasing or decreasing, the death rate, birth rate, age at first breeding and fecundity must be known. Death rates and birth rates can be affected by many factors. Factors that may affect death rates include: food availability, predation, disease and oil spills. The study of factors that affect population change is called demography.
Some ecological and demographic findings by the CWE (Centre for Wildlife Ecology at Simon Fraser University) and their partners at Desolation Sound, B.C. include:
|Marbled Murrelet Biology|
|Status of the Marbled Murrelet in Canada|
|Marbled Murrelet Recovery Team|
|Marbled Murrelet Research and Population Estimates|