Alaska Bird Observatory

Denali Institute Migration Station

1999 Annual Report 

Migration monitoring stations provide valuable information for monitoring local population trends in migrant birds (Dunn et al. 1997). The Denali Institute Migration Station (DIMS) is one of 150 migration monitoring stations located throughout North America. The primary objectives of DIMS are: 1) to capture and band migrating passerines to examine population dynamics, the phenology of migration, and the timing of life history events (e.g. migration, reproduction, molt, juvenile dispersal, and seasonal differences in body condition); and 2) to provide public education programs relating to avian ecology and conservation.

DImS is located in the heart of Denali National Park and Preserve, approximately 210 km southwest of Fairbanks, Alaska. The study area is located at approximately 6,70 m elevation in the Moose Creek drainage, one of the few clear-running anadramous rivers in Denali National Park and Preserve. The migration station is located on a west-facing slope on Camp Denali Property. Vegetation in the riparian flood plain of Moose Creek consisted of balsam poplar (Populus balsamifera.) in the upperstory, and soapberry (Shepherdia canadensis) and willows (Salix spp.) in the understory. Above the riparian zone the vegetation changed abruptly into shrub species dominated by dwarf birch (Betula nana) with alpine blueberry (Vaccinium uliginosum), labrador tea (Ledum sp.), and crowberry (Empetrum nigrum).

Staff from the Alaska Bird Observatory and Denali Institute operated 10 standard mist nets (2.6 m x 12 m, 30 mm mesh) from 17 July to 10 September. The station was operated daily, weather permitting, for 7 hours beginning at sunrise. We altered the station set up that was established in 1998 because we captured more birds than we could safely process that year. The following combination of factors made the 1998 station set up too aggressive for our field crew: extremely high capture rates of birds; nets spread too far apart across a steep hillside to complete net runs quickly; and inability to house large field crews because of logistical constraints. We therefore reduced the size of the station so that a small field crew could operate it long term and minimize the risks to birds. Our goals were to have a station where nets could be checked at 20-minute intervals, when necessary, and to reduce the number of birds captured to a manageable and safe level. Frequent net runs over a smaller area would allow a field crew to adequately handle large volumes of birds.

All birds captured were banded with United States Fish and Wildlife Service numbered bands. Data were recorded noting species, age, sex, wing chord and tail lengths, mass, date and time of capture, net site, furcular fat score, reproductive condition (cloacal protuberance or incubation patch), age (degree of skull pneumatization), and molt scores.

Relative Abundance

We banded 767 birds of 30 species during 2,361 net hours of during 1999 (Table 1). Wilson’s Warblers were the most abundant species (46% of all individuals banded), followed by White-crowned Sparrows (15%), Slate-colored Junco’s (7%), Orange-crowned Warblers (6%), and Swainson’s Thrushes (4%). Ten birds that were banded in 1998 were recaptured in 1999.

The species composition of captures during 1999 was similar to 1998; however, the capture rate for all species combined was 58% lower in 1999 (Table 2). Seventy-eight percent of the individuals captured are designated as priority species for monitoring because they are not adequately monitored by other protocols (Blancher et al. 1994). In order to monitor long-term population trends for a species, at least 10 individuals must be captured annually (Hussell and Ralph 1998). Fourteen species captured met this criterion at DIMS during 1998 and 1999.

Timing of Migration

Timing of captures was fairly similar between 1998 and 1999 (Fig 1). The majority of captures at this study site occur between 30 July and 5 September. These data suggest that these are the most important dates for migration banding, and are the minimum time nets should be operated.

Net Analysis

We compared capture rates in nets operated in 1999 with the same four nets operated in 1998 to determine whether the lower capture rates during 1999 could be attributed to the different net arrangement. Three of four nets showed decreased capture rates in 1999. The four nets combined showed a 28% decrease in capture rates between the two years; these data indicate that lower bird abundance could not be attributed to the net arrangement.

Education

Approximately 215 people visited the banding station during 1999. Guests were greeted by staff and volunteers at the migration station and were given a presentation relating to avian ecology and conservation. Feedback from guests attending banding demonstrations was very positive. Additionally, ABO biologists gave approximately seven evening presentations relating to songbird conservation in Alaska. Approximately 15 people attended each of these presentations for an estimated total of 105 people throughout the summer.

Two individuals successfully completed an eight-week banding internship. Both interns received extensive training in passerine banding and aging techniques. Together, they processed 60% of the birds captured at the station under the direct supervision of a skilled biologist. Their skills improved dramatically and each now qualify for positions that require proficient bird-banding skills.

The high number of birds captured at DIMS during 1998 surpassed our expectations for this study site; however, captures during 1999 were more comparable with capture rates at other migration stations in Alaska. It is impossible to determine the exact cause for the lower capture rates in 1999, but two factors in combination may have resulted in fewer birds captured. First, we altered the station set up by eliminating highly productive nets that were located at the top of a steep hill; it is likely that eliminating these nets resulted in lower overall captures for the entire station. This was our primary objective when we altered the net array. Second, capture rates for four nets operated during both years were 28% lower than in 1999. These data indicate that fewer birds moved through the study site in 1999. We suggest the more conservative net arrangement combined with lower numbers of birds were the likely cause of the lower capture rates during 1999. We cannot define whether 1999 is a "normal" year and 1998 an anomaly based on only two years of data.

The DIMS should continue to be operated with the goal of long-term monitoring of bird populations. Despite the lower numbers of birds captured during 1999, this site could be used to effectively monitor 10 to 14 species of birds based on sample-size requirements proposed by Hussel and Ralph (1998), i.e., at least 10 and preferably 20 individuals within a species. The species composition of captures at DIMS further demonstrates that this is a valuable monitoring site. Seventy-eight percent of the individuals captured are of species not adequately covered by the nationwide Breeding Bird Survey, which emphasizes the international importance of monitoring in the Moose Creek drainage. Migration-monitoring efforts, such as DIMS, are an important component to statewide bird conservation efforts.

We would like to thank the many volunteers who contributed to the success of this project. Dorinda Dutcher, a Camp Denali employee, spent many of her days off volunteering at the migration station. Kristine Sowl provided much-needed help by travelling from Fairbanks to volunteer for a two-week period. Suzanne Cardinal and Alan Brelsford worked as interns for eight weeks; their hard work and desire to obtain excellent field skills were instrumental to the success of the project. We thank Cathy Pohl for managing the migration station this year; her insight and expertise greatly improved the project. We are grateful to the Denali Institute for funding this project. Special thanks to Nan Eagleson, Bob Barni, and Jerryne Cole for their support in numerous ways throughout the year.

Table 1. Number of birds banded at Denali Institute Migration Station and percent change in capture rates: 13 July-30 August 1998and 18 July-10 September 1999. 

		Number Banded		Capture Rates		% change
Species	Migration Strategy	1998	1999	1998	1999
Belted Kingfisher	A	0	1	0.00	0.04
Downy Woodpecker	R	1	0	0.06	0.00
Hairy Woodpecker	R	0	1	0.00	0.04
Three-toed Woodpecker	R	0	1	0.00	0.04
Olive-sided Flycatcher	A	2	0	0.12	0.00
Western Wood-Pewee	A	2	0	0.12	0.00
Alder Flycatcher *	A	27	7	1.56	0.30	-0.81
Hammond's Flycatcher	A	2	3	0.12	0.13
Gray Jay	R	1	6	0.06	0.25
Black-capped Chickadee	R	8	21	0.46	0.89	0.92
Boreal Chickadee	R	12	16	0.69	0.68	-0.02
Arctic Warbler	P	5	4	0.29	0.17
Ruby-crowned Kinglet*	B	29	23	1.68	0.97	-0.21
Gray-cheeked Thrush *	A	34	22	1.97	0.93	-0.35
Swainson's Thrush *	A	112	33	6.48	1.40	-0.71
Hermit Thrush	B	3	3	0.17	0.13
American Robin	B	2	5	0.12	0.21
Varied Thrush *	B	19	8	1.10	0.34	-0.69
Northern Shrike	B	0	3	0.00	0.13
Orange-crowned Warbler *	A	94	41	5.44	1.74	-0.68
Yellow Warbler	A	14	5	0.81	0.21
Yellow-rumped Warbler *	B	49	31	2.83	1.31	-0.54
Blackpoll Warbler *	A	16	12	0.93	0.51	-0.45
Northern Waterthrush *	A	17	12	0.98	0.51	-0.48
Wilson's Warbler *	A	537	250	31.06	10.59	-0.66
American Tree Sparrow *	B	34	28	1.97	1.19	-0.40
Savannah Sparrow	B	7	8	0.40	0.34
Fox Sparrow *	B	20	11	1.16	0.47	-0.60
Lincoln's Sparrow	A	2	8	0.12	0.34
Golden-crowned Sparrow	B	1	3	0.06	0.13
White-crowned Sparrow *	B	150	111	8.68	4.70	-0.46
Slate-colored Junco	B	66	53	3.82	2.24	-0.41
Rusty Blackbird	B	0	1	0.00	0.04
Common Redpoll	B	22	6	1.27	0.25	-0.80
Total		1,288	737	74.49	31.22	-0.58
Net Hours		1,729	2,361
* Target species for migration monitoring programs. Designated by Blancher et al. (1994)
Migration Strategy-R=resident, A=Nearctic-Neotropical Migrant, B-Nearctic-Nearctic Migrant,

© 1992-2000 Alaska Bird Observatory, Inc.
These data is copyrighted 1992-2000 Alaska Bird Observatory, Inc. All rights are reserved. Posting of these data on the World Wide Web is not a waiver of that copyright or any other intellectual property rights associated with the data. No part of these data may be used except for viewing as displayed here by any persons without the prior written consent of Alaska Bird Observatory, Inc. For information regarding the use of this data please contact Alaska Bird Observatory at birds@alaskabird.org

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