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Mystery Murrelets: Monitoring Two Elusive Seabirds

A Kittlitz's murrelet in flight.
A Kittlitz’s murrelet in breeding plumage in flight.

TIM MELLING

Glacier Bay National Park and Preserve is a summer haven for two elusive seabirds: Kittlitz’s (Brachyramphus brevirostris) and marbled murrelets (B. marmoratus). Murrelets are small diving seabirds (about 10 inches, 8 ounces) that eat small schooling fish and are members of the Alcid family (including auks, puffins, and murres). Kittlitz’s murrelets are endemic to Alaska and Russia, whereas marbled murrelets range from southern California to Alaska. In Glacier Bay, Kittlitz’s murrelets nest in steep, rocky, recently deglaciated habitat and forage in glacially influenced waters. In contrast, marbled murrelets nest in old-growth forests and are more common in less silty waters.

Since 2011, the National Park Service has monitored Kittlitz’s and marbled murrelets in Glacier Bay National Park due to conservation concerns and because they are indicator species that integrate marine and terrestrial ecosystems. The primary monitoring objectives are to estimate the abundance and spatial distribution of Kittlitz’s and marbled murrelets in Glacier Bay to track their population status and to better understand factors that may influence population trajectories.

Methods

Murrelets are surveyed each July in Glacier Bay by two experienced observers stationed on the bow of a vessel. Observers record the number of each species and the distance and bearing from the vessel along transects. Allocation of sampling effort across space is proportional to expected densities of Kittlitz’s murrelets. Estimates of species-specific abundance account for detection probability and for uncertain species identification (Hoekman et al. 2013).

Key Results

  • High annual variation in estimated abundance of both species (Figure 1) likely reflects a combination of demography (births and deaths), imprecision in estimates, and movements in and out of Glacier Bay.
  • Marbled murrelet estimated abundance in 2022 (Figure 1) far exceeded previous estimates. Causes for the increase are unknown, but a potential source is the northward migration of post-breeding birds, which have reached Glacier Bay by early July from as far south as British Columbia.
Two figures showing abundance of two murrellet species over time.
Estimated abundance (with 95% confidence intervals) of Kittlitz’s (A, red circles) and marbled (B, yellow squares) murrelets in Glacier Bay (1,092 km2) during early July from 2011-2022.
  • In 2022, similar to previous years, Kittlitz’s murrelets were primarily aggregated in and around Hugh Miller Inlet and Reid Inlet in the upper West Arm of Glacier Bay (Figure 2) and were associated with glacially influenced waters near suitable nesting habitat.
  • Factors influencing lower estimated abundance of Kittlitz’s murrelets in 2022 and 2019 are unknown. However, anomalously warm ocean temperatures were observed in Glacier Bay (Murdoch and Goodwin 2022) and in the Gulf of Alaska (Danielson et al. 2022), which negatively impacted many marine species (Suryan et al. 2021).
  • Marbled murrelets were widely distributed across Glacier Bay (Figure 3). Similar to previous years, the highest densities occurred in the lower and mid-Glacier Bay, likely due to seasonal aggregations of small schooling fish and proximity to nearby conifer forests that provide suitable nesting habitat.
  • Contrasting population trajectories for Kittlitz’s and marbled murrelets in Glacier Bay suggest that differing factors likely influence their distribution and abundance. In addition to movements in and out of Glacier Bay by murrelets, dynamic and changing habitat conditions including increasing ocean temperatures and changes in tidewater glaciers likely play an important role in influencing their distribution and abundance.
Two side-by-side maps showing murrelet occurrence.
Figure 2 (left) Spatial distribution of Kittlitz’s murrelets (size of red circles denotes group size) observed during line transect surveys in Glacier Bay, July 2022 and Figure 3 (right) Spatial distribution of marbled murrelets (size of yellow circles denotes group size) observed during line transect surveys in Glacier Bay, July 2022.

Literature Cited

Danielson, S. L., T. D. Hennon, D. H. Monson, R. M. Suryan, R. W. Campbell, S. J. Baird, K. Holderied, and T. J. Weingartner. 2022. Temperature variations in the northern Gulf of Alaska across synoptic to century-long time scales. Deep Sea Research Part II: Topical Studies in Oceanography 203: 105155.

Hoekman, S. T., B. J. Moynahan, W. F. Johnson, and C. J. Sergeant. 2013. Glacier Bay National Park and Preserve Kittlitz’s murrelet monitoring protocol: Version KM-2012.1. Natural Resource Report NPS/SEAN/NRR-2013/735. National Park Service, Fort Collins, Colorado.

Hoekman, S. T., J. N. Womble, T. R. Ziomek, and C. L. Amundson. 2023. Monitoring Kittlitz’s and marbled murrelets in Glacier Bay National Park and Preserve: 2021 annual report. Natural Resource Report NPS/SEAN/NRR—2023/2559. National Park Service, Fort Collins, Colorado. doi:10.36967/2299439.

Murdoch, C. and D. Goodwin. 2022. Glacier Bay oceanography monitoring: 2020 update. National Park Service Resource Brief, Gustavus, Alaska.

Suryan, R. M., M. L. Arimitsu, H. A. Coletti, and 46 more. 2021. Ecosystem response persists after a prolonged marine heatwave. Scientific Reports 11: 6235. doi:10.1038/s41598-021-83818-5

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Glacier Bay National Park & Preserve

Last updated: April 23, 2024