2010 "Volunteers Working With Invasives"
Grants Report Form
PROJECT BACKGROUND INFORMATION
Impact of non-native caribou on Adak Island ecosystem function
Alaska Maritime National Wildlife Refuge, Aleutian Islands Unit
Name and Phone Number
Mark A. Ricca. 530-752-2505
(Up to 250 words)
Indigenous land mammals are absent from all but the most eastern islands of the Aleutian archipelago of Alaska. In 1958 at the request of the US Navy, 23 barren-ground caribou from the Nelchina herd on mainland Alaska were transplanted to Adak Island in the central archipelago. The resulting population grew to and remained stable at approximately 300 – 600 animals until the Naval Air Facility was decommissioned in the early 1990s. Subsequent aerial surveys indicate that the Adak herd has increased to over 3000 animals, most likely in response to dramatically reduced hunter harvest rates. Introduced ungulates (such as caribou) can significantly alter island community structure and nutrient processes, yet the strength and direction of caribou herbivory effects on Adak Island ecosystem processes have remained largely unexamined. For example, an exponentially growing population of caribou could dramatically over-exploit island resources as carrying capacity is exceeded. On the other hand, certain levels of caribou herbivory and subsequent nutrient input from caribou waste can increase plant primary production rates and soil nutrient availability, and facilitate conversion from heath to grass dominated plant communities. This study took the first step towards elucidating the impacts of 50 plus years of introduced caribou by conducting a pilot assessment of vegetation community structure and nutrient dynamics on Adak Island and nearby Kagalaska Island (a ‘caribou free island’).
List of Invasives Species Targeted:
Barren ground caribou
Project Completion Date
or Estimated Completion Date:
(Check all that apply)
Describe the type of work the volunteers performed. (Up to 150 words)
The volunteer was instrumental in assisting the project leader in all aspects of the field study, including preparation of field equipment, collection of plant and soil samples, plant identification, photo documentation, and caribou observations and enumerations. The volunteer also provided a valuable safety element to the project, whereby solo field work would have occurred in this remote location without volunteer involvement.
Total Number of Volunteers:
Total Number of Volunteer Hours:
List both new and existing partnerships utilized in this project. (Up to 150 words).
This project was led by the US Geological Survey-Western Ecological Research Center, and was designed to provided much needed data to biologists at the Alaska Maritime NWR on the impacts of introduced caribou on refuge lands. The project also leveraged expertise from faculty and analytical laboratories at the University of California, Davis. Furthermore, we are currently working with local Adak residents to obtain data on body condition of caribou entering winter.
Give an overview of the results of the project. Include quantifiable measure of success, such as maps produced, efficacy of control measures, number of sites where invasions were detected early and responded to, number of community contacts, etc. (Up to 250 words).
We sampled 275 plots on Adak and Kagalaska from July 30 to 12 September 2010. We stratified Adak into 3 levels of caribou summer density, and treated Kagalaska as a control based on prior USFWS surveys. We also opportunistically collected fecal samples for diet estimation (pending additional funds), and obtained measures of body condition from hunter killed animals. Although data have not been statistically analyzed to date, we observed the following patterns: • Pellet counts on Adak correlated with classified levels of caribou density. High caribou density plots had the highest graminoid cover and lowest lichen cover. In contrast, dwarf shrub cover was highest in low caribou density plots, and lichen cover and diversity was highest on Kagalaska. Forb cover and vascular plant species richness was similar across all caribou density levels. • Moss and litter layer depth was twice as high in the low caribou density and Kagalaska control plots compared to the moderate and high caribou density plots. • Although Kagalaska was classified as a ‘caribou free’ control island, we found small amounts of ca. 3-month old sign (scat and tracks) that indicated caribou at least ephemerally inhabit Kagalaska by swimming across the narrow strait from Adak. We did not visually observe caribou on Kagalaska during our surveys. • Adult males killed in late summer appear to be in good physiological condition based on a limited sample (n = 5) of necropsied hunter kills. • Samples collected for plant and soil nutrients are currently undergoing laboratory analyses.
Number of Acres Treated:
Number of Acres Inventoried and/or Mapped:
Number of Acres Restored:
Account for funds in broad categories such as equipment, volunteer stipends, travel, coordinator salary/contract, etc.
Total Grant Amount:
Breakdown of Expenditures:
Total $ Spent
% of Total Grant
Equipment / Supplies
Volunteer Coordinator Salary/Contract
How useful was this program for meeting refuge invasive species objectives and how can it be improved?
Continued documentation of caribou impacts is necessary for informed management decisions given the recent increase in the size of the introduced Adak caribou herd. Additional areas of high caribou density (namely the remote southern part of the island) require sampling to obtain a better measure of island wide caribou impacts. A larger and continuous sample of caribou body condition in late fall and early spring would provide an economical index of herd density relative to habitat conditions (i.e., is herd size exceeding winter carrying capacity?). Data on caribou movements from satellite telemetry would help determine how and when caribou are impacting particular habitats on Adak. Lastly, an aerial survey of Adak and Kagalaska is necessary to determine current caribou population size and trajectory, and whether or not caribou have become established on Kagalaska.
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