Neotropical migrant banding program at the University Field Station, Delta Marsh, 1994 and comparisons with 1992 and 1993 Keith A. Hobson Canadian Wildlife Service Saskatoon, Saskatchewan, Canada E-mail: hobsonk@saskatoon2.wxe.sk.doe.ca

Introduction

There is growing concern that neotropical migrant songbirds, those species that winter in the American neotropics and breed in temperate North America, appear to be declining dramatically (Robbins et al. 1989; Askins et al. 1990; papers in Hagan and Johnston 1992; Finch and Stangel 1993). Much of this concern is based on population trends that are well documented for migrants that move through and breed in the hardwood forests of the eastern United States BUT the status of populations of songbirds in the central prairie provinces of western Canada remains poorly understood. This is due, in part, to the low density of routes of the North American Breeding Bird Survey (BBS) occurring here and the fact that many of these species of neotropical migrants breed in forests that are not well suited to survey by the BBS.

In order to address this paucity of information, the Canadian Wildlife Service, in cooperation with the Long Point Bird Observatory, has created and supported migration monitoring stations at Beaverhill Bird Observatory in Alberta and at Last Mountain Lake in Saskatchewan. Constant effort mistnetting will help us establish indices of population status and reproductive success of several species that breed over broad geographic areas. However, these efforts will not allow us to establish historical population trends to date in this region. Fortunately, a unique banding study conducted in the early 1980s has provided an excellent opportunity to monitor longer-term population trends of warblers moving through south-central Manitoba.

From 1982 to 1984, Heidi den Haan, under the supervision of Dr. Spencer G. Sealy of the Department of Zoology, University of Manitoba, conducted regular spring and fall banding of warblers moving through the narrow dune forest along the south shore of Lake Manitoba. This area is an ideal location to mistnet migrant songbirds because it is bordered on one side by the Lake and on the other by Delta Marsh. Migrants are thus likely to stop at and move along this strip of forest before continuing on their way to breeding or wintering grounds. In early 1992, I approached Dr. Sealy and Heidi den Haan and suggested that, during the years 1992 through 1994, it would be appropriate to repeat a banding program at this site in order to evaluate possible population changes of these birds during the intervening decade. It was agreed that such a study was valuable and that unpublished data would be provided from the early 1980s so that such a comparison could be made. In addition, it was my ambition to use this study as a springboard for a permanent migration monitoring station at Delta Marsh. As a result of these discussions, the Canadian Wildlife Service allowed me to use personal Green Plan research funds to conduct the 3-year banding program at Delta Marsh from 1992 through 1994. The results of 1992 and 1993 operations are summarized in Hobson (1992) and Hobson (1993), respectively. This report summarizes the results of the 1994 fall banding program at Delta Marsh and presents preliminary analyses of banding at this site for the period 1992-94. When data are made available from the early 1980s, a historical comparison will be made.

Methods

During the 3-year study, eleven mistnets were established at the same positions as used previously by den Haan and Sealy in the early 1980s. These sites are located between the University Field Station and the Assiniboine River Diversion. All mistnets were standard 3x12 meter, four-tier design. In keeping with the 1982-84 protocol, half of the mistnets were 30 mm mesh and the other half were 36 mm mesh. Mistnets were operated typically for six hours after one half hour before sunrise and again for two hours in the late afternoon or early evening. Nets were checked every 20-30 minutes or more frequently when necessary. Nets were not operated in rain or heavy winds.

All birds were banded and mass, wing length, furculum fat level measured. In addition, where possible, age and sex was determined through plumage characteristics, skulling and evidence of breeding status (presence of a brood patch or cloacal protuberance). Presence of molt and feather wear was also recorded for each individual. During the banding season of 1993, blood and feather samples were taken from a subset of birds captured to be used in genetics and stable-isotope analysis. Starting in 1993, we also incorporated several recommendations of the Long Point Bird Observatory (LPBO). In particular, we established Daily Estimate Totals (ET) of all birds recorded in the vicinity of our banding station. As originally conceived at LPBO, the ET was designed to incorporate the advantages of several sampling procedures while minimizing the disadvantages of relying on any single method. At Delta Marsh, the ETs are based on banding totals, a daily hour-long census along a route incorporating the Ridge forest, Delta Marsh and the shoreline of Lake Manitoba, and other incidental but more or less continuous observations by banders and observers.

Results

Data are currently being analyzed for weather effects by Dr. Ken Jones of the Department of Environment in Saskatoon. If significant correlations can be found between species capture rate and environmental conditions, then data will be normalized before comparison both within and between decades. From 1 July through 30 September 1994, 5,877 captures were recorded representing 81 species (Table 1).

Table 1. Bird banding data from 5 July through 30 September 1994 at the University Field Station (Delta Marsh).

Common Name	Code	Latin name	No.
Yellow Warbler	YWAR	Dendroica petechia	1435
Tennessee Warbler	TEWA	Vermivora peregrina	1100
Myrtle Warbler (Yellow-rumped)	MYWA	Dendroica coronata	432
Northern Waterthrush	NOWA	Seiurus novaboracensis	211
Least Flycatcher	LEFL	Empidonax minimus	210
Common Yellowthroat	COYE	Geothlypis trichas	199
American Redstart	AMRE	Setophaga ruticilla	179
Song Sparrow	SOSP	Melospiza melodia	155
Tree Swallow	TRES	Tachycineta bicolor	125
Baltimore Oriole	BAOR	Icterus galbula	124
White-throated Sparrow	WTSP	Zonotrichia albicollis	123
Nashville Warbler	NAWA	Vermivora ruficapilla	109
House Wren	HOWR	Troglodytes aedon	104
Ruby-crowned Kinglet	RCKI	Regulus calendula	99
Swainson’s Thrush	SWTH	Catharus ustulatus	92
Warbling Vireo	WAVI	Vireo gilvus	86
Gray Catbird	GRCA	Dumetella carolinensis	79
Black-and-white Warbler	BAWW	Mniotilta varia	67
American Robin	AMRO	Turdus migratorius	62
Ovenbird	OVEN	Seiurus aurocapillus	55
Orange-crowned Warbler	OCWA	Vermivora celata	51
Blackpoll Warbler	BLPW	Dendroica striata	50
Slate-colored Junco	SCJU	Junco hyemalis	45
Magnolia Warbler	MAWA	Dendroica magnolia	40
Red-winged Blackbird	RWBL	Agelaius phoeniceus	37
Rose-breasted Grosbeak	RBGR	Pheucticus ludovicianus	32
Hermit Thrush	HETH	Catharus guttatus	31
Chipping Sparrow	CHSP	Spizella passerina	28
Cape May Warbler	CMWA	Dendroica tigrina	25
Orchard Oriole	OROR	Icterus spurius	24
Canada Warbler	CAWA	Wilsonia canadensis	23
Morning Warbler	MOWA	Opornis philadelphia	21
Cedar Waxwing	CEDW	Bombycilla cedrorum	19
Eastern Wood-Pewee	EAWP	Contopus virens	19
Traill’s Flycatcher	TRFL	Empidonax traillii	19
Black-billed Cuckoo	BBCU	Coccyzus erythropthalmus	17
Chestnut-sided Warbler	CSWA	Dendroica pensylvanica	17
Eastern Kingbird	EAKI	Tyrannus tyrannus	17
Eastern Phoebe	EAPH	Sayornis phoebe	16
American Goldfinch	AMGO	Carduelis tristis	15
Barn Swallow	BARS	Hirundo rustica	15
Red-eyed Vireo	REVI	Vireo olivceous	15
Western Palm Warbler	WPWA	Dendroica palmarum	13
Brown-headed Cowbird	BHCO	Molothrus ater	12
Clay-colored Sparrow	CCSP	Spizella pallida	12
Common Grackle	COGR	Quiscalus quisaula	12
Fox Sparrow	FOSP	Passerella iliaca	12
Philadelphia Vireo	PHVI	Vireo philadelphicus	12
Pine Siskin	PISI	Spizella pinus	12
Blackburnian Warbler	BLBW	Dendroica fusca	11
Brown Creeper	BRCR	Certhia familaris	10
Gray-cheeked Thrush	GCTH	Catharus minimus	10
Lincoln’s Sparrow	LISP	Melospiza lincolnii	10
Marsh Wren	MAWR	Cistothorus palustris	10
Wilson’s Warbler	WIWA	Wilsonia pusilla	10
Downy Woodpecker	DOWO	Dendrocopos pubescens	9
Yellow-shafted Flicker	YSFL	Colaptes auratus	9
Bank Swallow	BANS	Riparia riparia	8
Solitary Vireo	SOVI	Vireo solitarius	8
Golden-crowned Kinglet	GCKI	Regulus satrapa	7
Red-breasted Nuthatch	RBNU	Sitta canadensis	7
Yellow-bellied Sapsucker	YBSA	Sphyrapicus varius	7
Bay-breasted Warbler	BBWA	Dendroica castanea	6
Mourning Dove	MODO	Zenaida macroura	6
Yellow-bellied Flycatcher	YBFL	Empidonax flaviventris	6
Swamp Sparrow	SWSP	Melospiza georgiana	5
Black-throated Green Warbler	BTNW	Dendroica vireus	4
Hairy Woodpecker	HAWO	Dendrocopos villosus	4
Sharp-shinned Hawk	SSHA	Accipiter striatus	4
Purple Finch	PUFI	Carpodaccus purpureus	3
White-breasted Nuthatch	WBNU	Sitta carolinensis	3
Connecticut Warbler	CONW	Opornis agilis	2
Rufous-sided Towhee	RSTO	Pipilo erythrophthalmus	2
Veery	VEER	Catharus fuscescens	2
Black-throated Blue Warbler	BTBW	Dendroica caerulescens	1
Great-crested Flycatcher	GCFL	Myiarchus crinitus	1
Harris’ Sparrow	HASP	Zonotrhichia querula	1
Northern Cardinal	NOCA	Cardinalis cardinalis	1
Olive-sided Flycatcher	OSFL	Contopus borealis	1
Yellow-headed Blackbird	YHBL	Xanthocephalus xanthocephalus	1
Yellow-throated Vireo	YTVI	Vireo flavifrous	1

For 28 species representing at least 35 unique captures in any given year, the phenology of capture at the study site are presented in Appendix 1. Relative capture rates of 28 most abundant species are presented in Fig. 1. For 1992, 1993 and 1994, nets were operated between 07:00 and 12:00 h for 2,916.9, 4,027.3 and 4,674 net hours, respectively.

Comments

Phenology of migration was consistent between years for most species with the exception of American Redstart that showed an earlier passage in 1994 compared to previous years. Yellow Warbler, Song Sparrow and Least Flycatcher captures involved resident breeding and hatch-year birds as well as migrants.

Relative abundance of most species did not change significantly between years with the notable exception of Tennessee Warblers that peaked in 1994 compared with the previous two years. Tennessee Warblers are specialist feeders of spruce budworm and are known to undergo large population fluctuations. Variation in numbers of tree swallows reflects changes in effort for that particular species (i.e. not all captured birds were banded during busy periods). Breeding Yellow warblers departed earlier from the Ridge in 1993 compared with other years and so their relative abundance values may also be misleading. More detailed analysis of all species awaits correction of data after consideration of weather effects.

Future Direction

Banding will continue at the University Field Station as part of the Delta Marsh Bird Observatory. This non-profit organization will maintain a constant effort mistnetting operation that will form part of a national network that is supported by the Baillie Birdathon and the Canadian Wildlife Service. In addition to regular banding, this facility will also serve as a research node for studies of migrating songbirds. For further information, please contact the author or Heidi den Haan (R.R. #1, Box 1, Portage la Prairie, Manitoba, R1N 3A1, 204-239-4287).

Acknowledgements

This project has benefitted from the efforts of several staff and volunteers. In particular, I thank Paula Grieef, Heidi den Haan, Enid Cumming, and Marlene Gifford. Dr. Spencer G. Sealy and Heidi den Haan kindly consented to provide their banding data from the early 1980s. Special thanks to the staff and students of the University Field Station (Delta Marsh) for their enthusiasm and support. Financial assistance was provided by research support to myself from the Canadian Wildlife Service and grants from the James L. Baillie Memorial Fund, Canada Trust (Friends of the Environment Foundation) and The Friends of the Field Station.

References

Askins, R. A., Lynch, J. F. and Greenberg, R.. 1990. Population declines in migratory birds in eastern North America. In: Power, D.M. (ed.) Current Ornithology. Volume 7: 1-57. New York: Plenum Publishing.

Finch, D. M. and Stangel, P. W.(eds.). 1993. Status and Management of Neotropical Migratory Birds; 1992 September 21-25; Estes park, CO. Gen. Tech. Rep. RM-229. Fort Collins, CO; U.S. Dept. Agric. 422 pp.

Hagan, J. M. and Johnston, D. W. 1992. Ecology and Conservation of Neotropical Migrant Landbirds. Smithsonian Inst. Press, Washington. 609 pp.

Hobson, K. A. 1992. Neotropical migrant banding program at the University Field Station, Delta Marsh. University Field Station (Delta Marsh) Annual Report 27: 55-56.

Hobson, K. A. 1993. Neotropical migrant banding program at the University Field Station, Delta Marsh, 1993. University Field Station (Delta Marsh) Annual Report 28: 45-46.

Robbins, C. S., Sauer, J. R., Greenberg, R. S. and Droege, S.. 1989. Population declines in North American birds that migrate to the neotropics. Proc. Natl. Acad. Sci. 86: 7658-7662.