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.

Marbled Murrelet Population Estimates

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:

  • Radar surveys: One method used to count Marbled Murrelets in specific watersheds is radar surveys. Radar is a tool for locating objects using high frequency radio waves. Radio waves are emitted by the radar device and when they hit an object they bounce back. By detecting returned signals the radar unit can identify the location of objects. Marbled Murrelet researchers use radar to detect Marbled Murrelets flying in and out of coastal inlets. Radar surveys are conducted in the two hours before dawn and the first hour after dawn, when the birds are flying to and from their nesting areas. Crews deploy radar either from an anchored boat or on land at the mouth of a coastal inlet. Murrelets can be distinguished from other birds because they fly faster than other birds and they commute from their feeding to nesting areas in a straight line. Radar surveys have been conducted in the Clayoquot Sound region, the Sunshine Coast, the Central Mainland coast, the north coast, and the northwest coast of Vancouver Island. An important result from the Clayoquot study is that radar counts at 18 watersheds were significantly correlated with total watershed area, areas of mature (> 140 yrs. old) forest and, most strongly, with areas of mature forest below 600m. With the removal of old growth forests, murrelets evidently moved elsewhere and did not pack into the remaining old growth patches at higher densities.
  • At-sea surveys: The purpose of at-sea surveys is to count Marbled Murrelets on coastal waters where they feed. Boats follow pre-set routes called transects and trained observers count Marbled Murrelets within a fixed distance of the boat (often 50 m). The transects are usually 5-10 km long and run parallel to the shoreline. Transects are set at fixed distances from the shoreline and are commonly done 200 and 600 m out from the surfline.

Marbled Murrelet Research

Major focuses of Marbled Murrelet research in B.C. have concentrated on locating nesting sites, and on Marbled Murrelet ecology and demography. nest

Nesting Site Research

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.crbliffheli.jpg (22635 bytes)Crbcliffnest.jpg (20254 bytes)










Terrestrial Surveys

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:

  • Occupied detections: Looking and listening for adult murrelets to determine occupied detections. An occupied detection is when Marbled Murrelets are seen or heard landing on branches, perching or flying below, through or out of the forest canopy. Although the actual nests are not found using this method, occupied detections provide an indicator of the types of habitats used by Marbled Murrelets. Map of occupied detections survey locations in B.C. (from SFU group)
  • Tree climbing: Forest areas are surveyed for trees that are suitable for Marbled Murrelet nests and then trees are climbed by professionals to determine if nests are present. Comparisons between different types of habitat have been conducted by selecting plots at random within each habitat type followed by a search for nests using tree climbing.
  • Following flight paths: Marbled Murrelets are observed on successive days whilst they fly into particular areas. Researchers ‘home in on’ the nest by observing murrelets on their specific flight paths to and from the nest. Every day they get closer and closer to the nest until they observe a bird at the nest.
  • Nesting evidence: Researchers search the forest floor for signs of nests such as egg shells fragments or chicks that have fallen out of nests and perished.

Radio Telemetry

cateli.jpg (16712 bytes)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).

Marbled Murelet Ecology and Demography

Canasaldisk.jpgIn 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:

  • Fecundity estimate for Marbled Murrelets: .15 - .22. Fecundity is the number of fledged females produced per adult female per year.
  • Marbled Murrelets can live to at least 9 years
  • Annual adult survival estimate for 1991-2000 is 0.83 (0.72-0.90, 95% confidence interval)
  • A two year old Marbled Murrelet was discovered with a brood patch, indicating that they may breed as early as two.
Marbled Murrelet Biology
Status of the Marbled Murrelet in Canada
Marbled Murrelet Recovery Team
Marbled Murrelet Research and Population Estimates