ABO Research - Tok River 2001

HABITAT SELECTION OF BIRDS BREEDING IN THE TOK RIVER WATERSHED
PROGRESS REPORT 2000-2001
September 2001

U.S. FISH AND WILDLIFE SERVICE
Tetlin National Wildlife Refuge
Tok, Alaska 99780

Portions of state forest in the Tok River watershed are to be logged in the next few years, offering a rare opportunity to study how breeding birds in Interior Alaskan taiga are affected by large scale changes to their habitats. This requires understanding the nature of these birds’ relationships with habitat features. This project was therefore initiated with two major aims: 1) Examine the responses of breeding birds to landscape-level disturbance caused by logging in the boreal forest; 2) Gain insight into macro- and micro-habitat preferences of birds breeding in the boreal forest. We censussed birds, surveyed vegetation and recorded abiotic habitat factors at randomly selected points in the Tok River watershed in June 2000. The following June we returned to previously visited points to re-census birds and record any dramatic changes to habitat. We hope to continue returning to census points for two more seasons in order to compare data sets acquired before and after logging takes place. Preliminary examination of the data indicates that avian species composition and habitat preferences in the study area are similar to elsewhere in Interior Alaska, except for the unexpected absence of Townsend’s warblers (Dendroica townsendii) from mature white spruce (Picea glauca) stands.

Thanks to Alaska Bird Observatory, the U.S. Fish and Wildlife Service, and the Skaggs Foundation for funding this project. Staff at Alaska State Division of Forestry, especially Gordon Worum, provided invaluable remote sensing data and GIS support. Tom Paragi and others at Alaska Department of Fish and Game assisted with logistics and bear safety considerations. Tetlin National Wildlife Refuge kindly provided housing, office space, and various equipment. Refuge biologists Bud Johnson and Keith Larson offered expertise and assistance whenever possible. Nancy DeWitt at Alaska Bird Observatory worked to secure funding and field staff.

PROJECT PERSONNEL:

Anna-Marie Benson, Ornithologist, Principle Investigator
Marin Sardy, Biological Technician
Ram Papish, Biological Technician
Jennifer McGrath, Volunteer Field Technician
Marta McWhorter, Volunteer Field Technician

COOPERATORS:

Jeff Sanchez, Biological Technician
Tom Sardy, Volunteer

This project was initiated to examine some of the relationships among Interior Alaska forest bird populations, their habitats, and large-scale changes that occur within these habitats. The Tok River valley was chosen as the study site when the area was slated to be logged. Logging operations in a large proportion of the old-growth white spruce (Picea glauca) along the Tok River offer a rare opportunity to evaluate the effects of one such change - timber harvest - on forest avifauna. The mosaic of vegetation types that comprise the Tok River watershed enable examination of how logging in one habitat type affects avian populations in both logged areas and adjacent unaltered habitats. In addition, the majority of cutting is taking place within 0.5 miles of the Tok River. Such riparian corridors are of interest to biologists and wildlife managers in Interior Alaska, as they are vital pathways for migratory birds moving to and from their breeding grounds. Logging in riparian zones may therefore seriously impact populations of birds breeding elsewhere in the state. This study will provide baseline ecological data on avian habitat relationships in Alaskan boreal forests, and illuminate how these relationships are affected by major disturbances within the taiga ecoregion. The results of this project will provide better understanding of these processes and valuable comparative data, on which land and wildlife management professionals may base future conservation and land-use decisions.

The primary objective of this study is to examine avian distribution among the river corridor’s dominant habitat types, and determine bird species’ patterns of use in the white spruce patches. The long-term objective of the study is to evaluate how landscape-level changes in interior Alaska boreal forest affect forest birds. Specific project objectives are as follows:

Cutting of white spruce in the Tok River watershed is scheduled to begin during the winter of 2001-2002. Data collection for this project began in June 2000. As of June 2001, almost all white spruce stands in the study area remained intact. This provides two seasons of pre-logging data to be compared with the post-logging counts that should be carried out in 2002 and 2003. Our ability to complete the next two seasons’ field work is contingent upon acquisition of funding and recruitment of qualified field staff.

The study area encompasses all land within half a mile of the river from just upstream of its confluence with the Little Tok River, to approximately 14 miles downstream near its intersection with Eagle Trail . The river valley is at 2000' elevation, and cuts through a ridge of Alaska Range peaks that steeply climb to approximately 6000' on either side of the valley. The terrain is flat and even throughout most of the study area, although permafrost heaves shape portions of the lowlands, and in some areas the site boundaries reach up onto the steep-sided ridges. The valley’s hydrology is complex and dynamic due to the combined influences of melt-freeze processes within the permafrost zones, fluctuating river levels, periodic floods, and long-term changes in the course of the river (e.g. formation of oxbows, deposition of sandbars). The resulting ecosystem is a patchwork of vegetation types at various stages of succession, following different successional paths dependent on substrate, drainage, and terrain.

Coniferous forest covers approximately 60% of the study area, and is dominated by black spruce (Picea mariana), white spruce (P. glauca), or both. Mixed coniferous-deciduous forest, deciduous forest, and shrubland comprise 15%, 8%, and 17% of the vegetation respectively. The dominant deciduous species are balsam poplar (Populus balsamifera), aspen (P. tremuloides) and paper birch (Betula paperifera). Shrublands are dominated by Salix spp. and various low bog shrubs such as Labrador tea (Ledum groenlandicum) and species of blueberry and cranberry (Vaccinium spp.). Some shrubland areas are dominated by graminoids, especially Eriophorum and Calamagrostis.

A major highway transects the northern edge of the study area, but human activity is minimal even on the road corridor. Land use has traditionally been limited to hunting and some logging. Signs of continued human presence include a network of ATV trails, a few bear bait sites, and clearcuts from small-scale logging operations in the northwest corner. There is no evidence of any sizeable burns occurring in the study area in recent history. As of today, the river corridor remains relatively undisturbed.

We divided the vegetation in the Tok River watershed into 14 distinct habitat types based on Veirick et al (1992) Classification Level IV. These categories were then adjusted to better reflect categories used by forest management professionals. We later added a separate category for birds associated directly with the river. Of these habitats, five characterized coniferous forests at various ages, heights, and densities. Three described mixed coniferous-deciduous forests, four described deciduous (<10% coniferous) woods, and two described shrublands. We used Geographic Information System (GIS) maps (Department of Forestry data) to quantify the proportion of area of each habitat type in the study area. We selected census point locations through a stratified random sampling design, with the number of points visited in each habitat corresponding to its total area. The exact locations of all points were entered onto the memory of a portable GPS device, which was used to find all points in the field. At each point, we censussed all birds detectable by sight or sound, and ascertained in which habitat type each was located. In 2000 we censussed birds and surveyed vegetation at 304 points. In 2001 we conducted repeat censuses of 272 points, on or near the same date as the preceding year. During repeat censuses, we recorded any landscape-level changes that had occurred at the points between years (e.g. logging), and factors that could affect bird detectability, such as weather. We intend to census these points again in 2002 and 2003.

During the 2000 field season we conducted a vegetation survey at each point, immediately after the bird survey. We designed the vegetation survey to focus on features most likely to influence habitat selection by breeding birds. Survey plots were circular and included all area within a 50-meter radius of the associated census point. On each plot, we coded and recorded tree species composition and average height; tree canopy cover; conifer percentage; standing dead tree percentage; shrub species composition, height, and percent cover; herb and ground layer species composition and percent cover. We also recorded relevant abiotic factors: presence/absence and type of water (stream, pond, lake, ephemeral); presence/absence and type of disturbance; and slope and aspect, if the point was on a slope. Weather variables were coded and recorded. Because judging height and cover of vegetation was a subjective process, these values were bracketed and coded as well. Samples of unknown plant species were collected and identified later.

Upon completion of the 2002 and 2003 censuses, the data will be analyzed for correlations between habitat variables and bird species presence/absence, with special attention to logging effects.

All field personnel attend a week-long training session, during which they learn proper census techniques and practice distance estimation. Before beginning work in the field, they are tested for competency. During the census period, field notes are taken each day to record information not included in the data forms. This includes insect activity, plant phenology, wildlife sightings, and logistical considerations. In addition, the crew leader keeps a field notebook, recording anything and everything that may be of interest to project personnel in the future. It is not necessary to sample vegetation every season. However, weather and disturbance data are recorded every year during return visits to points.

The position of each point is recorded in UTM coordinates before the count begins. When returning to previously visited points, we allow a margin of error of ten meters. At each point, we record all visual and auditory detections of birds during a period of eight minutes. Birds detected during the first five minutes are recorded separately from those detected in the final three minutes, so the data may be compared with studies that used five-minute point counts. Point counts are conducted between 6 June and 30 June, when singing rates peak and breeding birds are therefore most detectible (Peyton 1996). Before 6 June, some species have not yet arrived at the breeding grounds, and in the last week of June singing rates drop off significantly (pers. obs.). We conduct all point counts between 02:00 and 09:00, roughly corresponding to the seven-hour period beginning a half-hour before sunrise. These times were chosen based on surveys by Swanson and Nigro (1999).

At each point we record: species code; habitat in which first observed; distance and direction from observer; and mode of detection. Direction is estimated based on a 360-degree scale, with zero degrees at true north. Birds detected that are not using the census area (e.g. flyovers) are recorded separately. Birds that may have been previously counted at another point are not recorded. All individuals are counted, but those detected as part of a pair or family group are recorded as one observation, as they are not statistically independent. A bird detected during the census but not identified may be identified after the count ends by closer observation, if time permits. Censusing is discontinued when sustained winds become too loud to effectively hear singing birds, or when steady rain causes birds to stop singing.

Estimating distance accurately is difficult. It is subject to both observer bias and a variety of external causes. For instance, some species sing louder than others; sounds travel farther in some types of vegetation; and noise from wind or the river often interferes with detection. However, the ability to estimate distance has been shown to increase with practice, so proper training and familiarity with field conditions are essential. All field staff therefore undergo a week of training and testing before censussing begins. To further reduce the effects of bias, distance estimations are bracketed into categories.

We detected a total of 53 bird species over both years. In 2000, we visited 304 census points and detected 46 bird species. In 2001 we detected a total of 44 species when we re-visited 272 of these points. To compare the data between years, we examined the sets of all independent observations (e.g. individuals, pairs, broods) made by each point’s primary observer. This was necessary because some points were surveyed by only one person, while others were surveyed by two. We did, however, include detections made by secondary observers when compiling the species lists.

The total number of individual observations differed greatly between years, with over twice as many detections made in 2001 as in 2000. In both years, Dark-eyed junco (Junco hyemalis) was the most abundant species, with 294 detections recorded in 2000 and 482 in 2001. Swainson’s thrush (Catharus ustulatus) and yellow-rumped warbler (Dendroica coronata) followed as second and third most abundant. These species were also the most widespread. Both years, all three species occurred in at least 13 of 14 habitat types. Townsend’s warblers were notably absent from white spruce stands. Although they are common in similar habitats in this region, we detected only one individual in 2000 and four in 2001.

Peyton, P.W.C. 1996. 1996 Annual Report: Development of landbird monitoring protocols for national parks in Alaska. Unpublished report. National Park Service. Alaska Bird Observatory, P.O. Box 80505, Fairbanks, AK 99708. 54 pp.

Spindler, M. and B. Kessel. 1980. Avian populations and habitat use in interior Alaska taiga. Syesis. 13:61-104.

Swanson, S.A. and D.A. Nigro. 1999. Avian inventory for Yukon-Charley Rivers National Preserve: 1999 progress report. Unpublished report. National Park Service, 201 First Ave., Doyon Building, Fairbanks, AK 99701.

Veirick, L.A., C.T. Dyrness, A.R. Batten and K.J. Wenzlick. 1992. The Alaska vegetation classification. Gen. Tech. Rep. PNW-GTR-286. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 278 pp.