Ewert et al • KIRTLAND’S WARBLER SPRING MIGRATION 
13 
1987). comparable to the migration rates of 
Kirtland's Warblers sampled. 
Daily rates of migration by male Kirtland's 
Warblers were similar to some species, but other 
species travel at faster rates during spring 
migration. For instance, four Wood Thrushes 
migrating from Honduras and Nicaragua to 
Pennsylvania across the Gulf of Mexico in spring 
averaged 263 km/day (Stutchbury et al. 2009) and 
two Purple Martins (Prague subis ) averaged 281 
and 577 km/day during their spring migration 
from Brazil to Pennsylvania, a distance of 
—7.550 km. Similarly, five spring migrating 
Veeries (Cathants fuscescens) tracked with geo¬ 
locators. whose estimated migration distance 
ranged from 5,950 to 10.290 km. migrated faster 
(209-350 km/day) than Kirtland's Warblers 
(Heckscher et al. 2011). and an Aquatic Warbler 
(Aaocephcilm paliulicola) averaged 280 km/day 
within Africa during fall migration (Cramp 1992). 
Overall, however, daily rates of spring migration 
by these species and our estimates for male 
Kirtland's Warblers indicate that many near¬ 
passerines and passerines migrate at rates close 
to the upper range of migration rates reported in 
Newton (2008). 
We obtained estimates of the duration of 
migration for a small number of males during 
two spring migration seasons. Ecological, meter 
ological, physiological, and other factors that 
affect duration and rate of migration will be better 
understood (Fransson 1995. kaess 2008. Tottrup 
et al. 2008, Yohanncs et al, 2009. Stutchbury et al. 
2011) as geolocators and other techniques become 
available to follow larger numbers of individual 
birds throughout migration (Robinson et al. 2010. 
Bridge et al. 2011). It may then be possible to 
describe other aspects of Kirtland's Warbler 
migration and connectivity such as distribution 
of frequently used stopover areas, when and 
where along the migratory route Kirtland's 
Warbler are most vulnerable, and inter-seasonal 
interactions, important hut missing information 
needed to develop a comprehensive conservation 
program for the species. 
ACKNOWLEDGMENTS 
We thank ihe L'.S. Fish and Wildlife Service. Huron- 
Manistee National Forest, and Michigan Departmenl of 
Natural Resources for permission to enter Kirtland's 
Warbler Management units. The International Program of 
the L'SDA Forest Service. Michigan Department of Natural 
Resources, Smithsonian Institution, and The Nature 
Conservancy funded our work. We greatly appreciate the 
efforts of Andrew Fra/.ee, P. W. Huber, Samara Lawrentz, 
Ingeria Miller. Z.oko McKenzie, Ray Perez, Michael 
Petrucha. Keith Philippe. .1. R. Probsl, Montara Roberts, 
Robert Slcbodnik, S. .1. Sjogren, Jim Stevens, Mark 
Thomas, and Jerry Wcinrieh who searched for early- 
arriving color-handed birds in breeding areas. Joe Fargione, 
M. L. Herbert. Peter Kareiva. Krista Kirkham, Robert 
Lalasz. Christopher Rimmer. J. J. Nocera, Peter Weaver, 
and one anonymous reviewer provided suggestions that 
greatly improved the manuscript. Sagar Mysorekar pre¬ 
pared the figure. The work was done in cooperation with 
the Bahamas National Trust. Puerto Rican Conservation 
Foundation. University of Puerto Rico, and the Kirtland's 
Warbler Recovery Team. 
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