Migration Maps for Some North American Neotropical Migrants

Sam Droege and Charles Wetherill

The maps presented here depict, in a coarse fashion, the relative abundance of a select group of neotropical migrants during fall and spring migrations. Their purpose is to give you a general notion of what pathways each species takes as it travels north or south in North America during migration. These maps were used as handout materials in the 1993 Migration Monitoring Workshop. Data were scavenged from a diverse set of bird banding sites and counting programs (e.g., questionnaires from the 1993 workshop on landbird migration monitoring, bird banding files, published literature, Operation Recovery files, and internal reports.

Methods

Migration information for a site was judged adequate if it covered a wide geographic area on a single day (e.g., May Counts) or sampled birds on at least 1/2 the days over a minimum 2 months period during spring or fall migration. Data, from 75 sites, for 48 neotropical migrants with large portions of their breeding range located within the boreal forest zone were selected. Raw totals (counts or bandings) for each species were divided by the total count or catch for all 48 species to calculate that species' proportional count/catch at each site.

Proportions were used rather than a measure of catch/effort because in most cases effort information was not available. It was assummed that the relative catchability or sightability did not vary greatly (order of magnitude-wise) among sites. Proportions were dumped into a mapping program. For each species map the site with the largest proportion was given the largest circle on the map. The size of the other circles were scaled to the square root of the largest proportion. Locations with an X indicate that the site used a counting technique rather than netting.

These maps are most appropriately thought of as depicting the geographic distribution of migrants at counting or capture sites within North America. Interpretation is unfortunately limited in some regions due to lack of sites, especially during spring migration. Comparisons among species and between spring and fall for the same species are also limited both because of the distribution of numbers the scaling of proportions.

It should be noted that individual sites are only very coarsely comparable. Factors such as net placement, time-of-year of the observations, differences among counts (denoted with an X) and net captures (denoted with a circle) influence capture/sighting rates. Despite the numerous techniques employed among these sites coarse route patterns are apparent (e.g., coastal vs. interior). Such information will be useful in judging proposed sampling frameworks for migration monitoring and are pretty nifty in their own right.

Caveat Rehash:

Sites represent different collection techniques. Species have different probabilities of being detected or caught among sites. Proportions were used and were not standardized by effort. Each map was standardized to the largest proportional count for that species. A background X indicates a counting technique was used at that site. Few sites collected information on the same schedule of dates and times.

Species list (JPEG Sizes Average 25k):

 American Redstart - Fall|Spring
Barn Swallow - Fall|Spring
Bay-breasted Warbler - Fall|Spring
Black-and-White Warbler - Fall|Spring
Black-throated Green Warbler - Fall|Spring
Black-throated Blue Warbler - Fall|Spring
Blackburnian Warbler - Fall|Spring
Blackpoll Warbler - Fall|Spring
Canada Warbler - Fall|Spring
Cape May Warbler - Fall|Spring
Chestnut-sided Warbler - Fall|Spring
Cliff Swallow - Fall|Spring
Common Nighthawk - Fall|Spring
Common Yellowthroat - Fall|Spring
Connecticut Warbler - Fall|Spring
Dusky Flycatcher - Fall|Spring
Eastern Kingbird - Fall|Spring
Gray-cheeked Thrush - Fall|Spring
Hammonds Flycatcher - Fall|Spring
Least Flycatcher - Fall|Spring
MacGillivray's Warbler - Fall|Spring
Magnolia Warbler - Fall|Spring
Mourning Warbler - Fall|Spring
Nashville Warbler - Fall|Spring
Northern Waterthrush - Fall|Spring
Olive-sided Flycat cher - Fall|Spring
Orange-crowned Warbler - Fall|Spring
Ovenbird - Fall|Spring
Palm Warbler - Fall|Spring
Parula Warbler - Fall|Spring
Philadelphia Vireo - Fall|Spring
Red-eyed Vireo - Fall|Spring
Rose-breasted Grosbeak - Fall|Spring
Say's Phoebe - Fall|Spring
Solitary Vireo - Fall|Spring
Swainson's Thrush - Fall|Spring
Tennessee Warbler - Fall|Spring
Townsend's Warbler - Fall|Spring
Traill's Flycatcher - Fall|Spring
Tree Swallow - Fall|Spring
Violet-green Swallow - Fall|Spring
Warbling Vireo - Fall|Spring
Western Wood Pewee - Fall|Spring
Western Tanager - Fall|Spring
Wilson's Warbler - Fall|Spring
Yellow Warbler - Fall|Spring
Yellow-bellied Flycatcher - Fall|Spring


Neotropical Migrant Migration Survey Data

Bird Monitoring in North America

Migration Monitoring


created by Charles Wetherill