Alaska Bird Observatory

Denali Institute Migration Station

Introduction
Background Information
Study Area
Methods
Results
Discussion
Acknolwedgements

Introduction

The Alaska Bird Observatory (ABO) and the Denali Institute cooperatively operated a migration-monitoring station at Camp Denali Lodge in the Moose Creek Drainage during 1998. Our primary objective was to evaluate the potential of the Moose Creek Drainage for long-term migration monitoring. First, we determined whether we could monitor species that are not adequately monitored by the nation-wide Breeding-Bird Survey (BBS). Second, we determined whether there were adequate numbers of individuals captured within a species to determine long-term trends in population indices. Finally, we evaluated the staffing needs, and therefore costs, to operate the station consistently from year-to-year.

Background Information

Understanding movements and population dynamics of passerines has become an international concern due to recent documentation of population declines throughout North America (Rappole and McDonald 1994, Askins et al. 1990). The importance of establishing baseline data for species has been recognized usually after a species is threatened or endangered (O’Connor 1992). Long-term monitoring programs give important early warning signs of population declines. The baseline data collected at the Denali Institute Migration Station (DIMS) will allow land managers to set management priorities (e.g. habitat preservation) based on scientific data.

Recent analyses of data from standardized mist-netting stations confirm the usefulness of this method for studying the abundance and survivorship of migratory bird populations (Chase et al. 1997, Dunn et al. 1997, Johnson and Geupel 1996). The long-term objectives of ABO’s mist-netting programs are to capture and band migrating passerines to examine: 1) population dynamics; 2) the phenology of migration; 3) timing of life history events (e.g. migration, reproduction, molt, juvenile dispersal, and seasonal differences in body condition); and 4) to provide public education programs relating to avian ecology and conservation.

Data provided from DIMS helps meet objectives set by Partners in Flight (PIF). PIF is a comprehensive Neotropical migratory bird conservation program of applied management, monitoring, and research implemented cooperatively by state and federal governments, industry, conservation organizations, and academia from North, South, and Central America. ABO works cooperatively with Boreal Partners in Flight (BPIF) to establish landbird-monitoring sites in Alaska to detect declines in bird populations before they become threatened. Data collected at DIMS was presented at the annual BPIF meeting and will be incorporated into state-wide monitoring programs.

Study Area

The Denali Institute Migration Station is located at the boundary of the Denali National Park and Preserve, approximately 210 km Southwest of Fairbanks, Alaska. The study area is located at approximately 2,000 ft elevation in the Moose Creek Drainage, one of the few clear-running anadramous rivers in Denali National Park.

The migration station was operated on Camp Denali Property on a west-facing slope. Mist nets were located on a steep gradient rising 250 vertical feet from the lowest net to the highest. The two lowest nets were located in the riparian flood plain of Moose Creek. Vegetation in this area 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 alpine forest. Blueberry (Vaccinium spp.) and dwarf birch (Betula gladulosa) were the most prevalent shrub species above the riparian area. Mid-nets were located near tall willows (Salix spp.) and aspens (Populus tremuloides). Upper nets were in mixed forest of black spruce (Picea mariana) and paper birch (Betula papyrifera).

Methods

Birds were captured using ten standard mist nets (2.6 m x 12 m, 30 mm mesh) from 16 July to 30 August. We attempted to operate mist nets four days out of five-day sampling periods. Nets were opened at sunrise and closed seven hours later. The orientation of most nets was perpendicular to the movements of migrants through the drainage.

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

Results

Relative Abundance

We banded 1,289 birds of 27 species (Table 1) during our first season of migration monitoring at Camp Denali. There were at least 10 individuals banded for 18 species. Wilson’s Warblers were the most abundant species (42% of all individuals banded), followed by White-crowned Sparrows (12%), Swainson’s Thrush (9%), and Orange-crowned Warblers (7%). Eight-nine percent of the individuals captured were designated as priority species for monitoring because of their lack of monitoring in other protocols.

Table 1. Number of Birds Captured at Denali Institute Migration Station: 13 July-30 August 1998.
Species	Migration Strategy	Banded	Recaptured	Mortality	Grand Total
Downy Woodpecker	R	1			1
Olive-sided Flycatcher	A	2			2
Western Wood-Pewee	A	2			2
Alder Flycatcher *	A	27			27
Hammond's Flycatcher	A	2			2
Gray Jay	R	1			1
Black-capped Chickadee	R	8	2		10
Boreal Chickadee	R	12	5		17
Arctic Warbler	P	5			5
Ruby-crowned Kinglet*	B	29		1	30
Gray-cheeked Thrush *	A	34	2		36
Swainson's Thrush *	A	112	5		117
Hermit Thrush	B	3			3
American Robin	B	2			2
Varied Thrush *	B	19	1		20
Orange-crowned Warbler *	A	94	7	1	102
Yellow Warbler	A	14			14
Yellow-rumped Warbler *	B	49	6		55
Blackpoll Warbler *	A	16	1		17
Northern Waterthrush *	A	17	1		18
Wilson's Warbler *	A	537	24	7	568
American Tree Sparrow *	B	34	1		35
Savannah Sparrow	B	7			7
Fox Sparrow *	B	20			20
Lincoln's Sparrow	A	2			2
Golden-crowned Sparrow	B	1			1
White-crowned Sparrow *	B	150	40		190
Slate-colored Junco	B	66	15		81
Common Redpoll	B	22	8	1	31
Total		1,288	118	10	1,416
* Target species for migration monitoring programs. Designated by Blancher et al. (1994)
Migration Strategy-R=resident, A=Nearctic-Neotropical Migrant, B-Nearctic-Nearctic Migrant,

Timing of Migration

Timing of migration was difficult to quantify in this study because poor weather conditions prohibited us from operating the nets consistently. Large "fall outs" of migrants occurred from 8 August to 30 August, and peak capture rates occurred on 19 August (Figure 1). There appeared to be migratory movements until the last days of netting, suggesting migratory movements continue into September.

Productivity

We documented age of 98.5% of birds banded (1,269 individuals) using degree of skull ossification as primary indication, and plumage as a secondary indication. Eighty-two percent of individuals captured were juveniles, ie. hatch-year birds (Table 2). In most species, juveniles comprised the majority of captures; however, there were low percentages of juvenile captures for Alder Flycatchers, Varied Thrush, and Northern Waterthrush.

Table 2. Age classification of birds banded at Denali Institute Migration Station during 1998.
Species	Adult	Juvenile	Unknown	Total	% Hatch Year
Downy Woodpecker	1			1	0.00
Olive-sided Flycatcher	2			2	0.00
Western Wood-Pewee	2			2	0.00
Alder Flycatcher	19	6	2	27	0.24
Hammond's Flycatcher	1	1		2	0.50
Gray Jay		1		1	1.00
Black-capped Chickadee	2	6		8	0.75
Boreal Chickadee	2	9	1	12	0.82
Arctic Warbler	4	1		5	0.20
Ruby-crowned Kinglet	5	24		29	0.83
Gray-cheeked Thrush	6	26	2	34	0.81
Swainson's Thrush	27	81	4	112	0.75
Hermit Thrush		3		3	1.00
American Robin		2		2	1.00
Varied Thrush	8	9	2	19	0.53
Orange-crowned Warbler	13	80	1	94	0.86
Yellow Warbler	4	10		14	0.71
Yellow-rumped Warbler	6	42	1	49	0.88
Blackpoll Warbler	6	9	1	16	0.60
Northern Waterthrush	13	4		17	0.24
Wilson's Warbler	44	491	2	537	0.92
American Tree Sparrow	7	27		34	0.79
Savannah Sparrow	1	6		7	0.86
Slate-colored Junco	9	56	1	66	0.86
Fox Sparrow	3	16	1	20	0.84
Lincoln's Sparrow	2			2	0.00
Golden-crowned Sparrow		1		1	1.00
White-crowned Sparrow	31	118	1	150	0.79
Common Redpoll	11	11		22	0.50
Total	229	1040	19	1288	0.82

Consistency of Netting Effort

We operated the migration station for 31 out of the 39 scheduled netting days for a total of 1,729 of the desired 2,730 net hours. Therefore, we achieved only 63% of the targeted netting effort. Rainfall during the months of July and August was higher in 1998 than the mean number of inches during the previous seven years (Table 3).

Table 3. Inches of Rainfall during July and August Year July August 1990 4.42 4.77 1991 3.79   1992 2.64 1.02 1993 2.67 2.80 1994 0.76 1.66 1995 2.32 2.32 1996 1.61 3.38 1997 3.03 3.68 1998 4.56 3.45 Mean (1990-97) 2.66 2.89

Releases

Migration fall outs occur in migration funnels during adverse weather (Richardson 1990). On several occasions, our banding crew could not keep up with the massive fall outs of birds that occurred at this site. If the crew was unable to process all birds quickly, nets were closed or birds were released at the net. It is difficult to estimate the number of unbanded birds that were released, but we estimate that on August 9, 22, and 29 we released 44, 48 and 86 birds, respectively, without bands.

Mortalities

The accepted mortality rate for similar netting programs is 1.0-2.0% (Ornithological Council 1997). Our mortality rate of 0.7% (Table 1) was below the accepted average.

Discussion

The high number of birds captured at DIMS surpassed our earlier expectations. The Moose Creek Drainage is clearly a migration funnel for many species of birds that breed in the subarctic. The number of individuals captured indicates this site could effectively monitor several species of birds. At least 10 and preferably 20 individuals within a species are required for long-term monitoring (Hussel and Ralph 1998). Therefore, eighteen species have monitoring potential at DIMS (Table 1).

The species composition of captures at this site demonstrates that DIMS may be a valuable monitoring site. Eighty-nine percent of the individuals captured are of species not adequately covered by the nationwide Breeding-bird Survey. These numbers indicate the international importance of monitoring in the Moose Creek Drainage.

The unusually high precipitation during July and August of 1998 constrained our ability to operate the migration station as frequently as necessary for monitoring movements of birds. Continued monitoring is needed to determine if rainfall at this site adversely affects consistent data collection. The efficiency of operating the nets could be improved for future years to increase the frequency of netting. This could be accomplished through increased staffing and a reevaluation of the number and placement of the nets.

Acknowledgements

We would like to thank all of the Camp Denali staff and the many volunteers who helped at the migration station. Quinn Emmering and Judy Williams contributed a large amount of time when we needed it most. We are grateful to the Denali Institute for implementing and funding this project. Special thanks to Nan Eagleson, Bob Barni, and Jerryne Cole for logistical support.

Literature Cited

Askins, R.A., J.F.Lynch, and R. Greenberg. 1990. Population declines in migratory birds in eastern North America. Curr. Ornithol. 7: 1-57.

Chase, M.K., Nur, N. and G.R. Geupel. 1997. Survival, productivity, and abundance in a Wilson’s Warbler population. Auk 114(3): 354-366.

Dunn, E.H., D.T. Hussell, and R.J. Andams. 1997. Monitoring songbird population change with autumn mist netting. J. Wildl. Manage. 61(2): 389-396.

Hussell, D.J.T and C.J. Ralph. 1998. Recommended methods for monitoring bird populations by counts and captures of migrants. Unpublished report for the intensive sites technical committee of the Migration Monitoring Council. Ontario Ministry of Natural Resources. P.O. Box 5000, Maple, Ontario, Cananda, K1A OH3.

Johnson, M.D. and G.R. Geupel. 1996. The importance of productivity to the dynamics of a Swainson’s Thrush population. Condor 98: 133-141.

O’Connor, R.J. 1992. Trends in Population: Introduction. in: Ecology and Conservation of neotropical Migrant Landbirds, (J.M. Hagan and D.W. Johnson, eds.), Smithsonian Institution Press, Washington, pp. 23-25.

Rappole, J.H., and M.V. McDonald. 1992. Cause and effect in population declines of migratory birds. Auk 111: 652-660.

Richardson, W.J. 1990. Timing of bird migration in relation to weather: updated review. pp 78-101 in Bird Migration: Physiology and Ecophysiology (E. Gwinner, Ed.). Springer-Verlag, Berlin.

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