The Wilson Journal of Ornithology 124(1 ):9-14. 2012 
DURATION AND RATE OF SPRING MIGRATION OF 
KIRTLAND’S WARBLERS 
DAVID N. EWERT, 16 KIMBERLY R. HALL, 1 JOSEPH M. WUNDERLE JR., 2 
DAVE CURRIE. 2 ’ SARAH M. ROCKWELL. 4 
SCOTT B. JOHNSON/ 5 AND JENNIFER D. WHITE 2 ’ 
ABSTRACT.—The duration of migration of the endangered Rutland's Warbler (Setophaga kirtlandii) has not been 
previously documented. We estimated the average duration of spring migration for five male Kirtland's Warblers by 
observ ing uniquely color-handed indiv iduals at or near both the beginning and end of spring migration in Eleuthera. The 
Bahamas, and Michigan, respectively. We estimated the average duration of spring migration for these live individuals to 
have been no more than 15.8 days (range 13-23 days) and the average distance traveled to have been 144.5 km/day (96.1 — 
169.1 km/day). Received 12 April 2011. Accepted II November 2011. 
The migratory period is typically the most 
poorly understood aspect of a migratory species' 
life history (Faaborg et al. 2010a. b) because of 
difficulties in studying birds during migration. 
This information gap constrains our ability lo 
comprehensively describe population demograph¬ 
ics, and reduces our ability to effectively imple¬ 
ment conservation measures (Faaborg el al. 
2010a. b) as mortality of adult migratory song¬ 
birds is apparently high during migration (Sillctt 
and Holmes 2002). Lack of information on 
duration of migration, and its relationship to 
breeding and wintering season conditions, limits 
our ability lo infer sensitivity of populations to 
changes in the amount and distribution of habitat 
required by migrating birds (Faaborg ct al. 
201 Ob). The challenge of understanding duration 
of migration, and integrating this information into 
models of avian population dynamics, is pressing 
for rare migratory landhirds that are infrequently 
observed during migration. 
Models that help explain duration of migration 
are complex, as many possible intrinsic (c.g.. 
body condition, experience) and extrinsic (e.g.. 
weather, habitat distribution, stopover site condi¬ 
tions) factors influence rates and total duration of 
The Nature Conservancy. 101 East Grand River 
Avenue. Lansing. MI 48906. USA. 
International Institute of Tropical Forestry. USDA 
Forest Service, Sabuna Field Research Station. MC 02 
box 6205, Luquillo, Puerto Rico 00773. 
Puerto Rican Conservation Foundation, P. O. Box 
362495. San Juan. Puerto Rico 00936. 
Department of Biology. University of Maryland, 
College Park. MD 20742. USA. 
Department of Biology. St. Mary's College of Mary¬ 
land. St. Mary's City. MD 20686, USA. 
"Corresponding author; e-mail; dewert@tnc.org 
migration. For example, Cochran and Wikelski 
(2005) developed a model for Catharus thrushes 
based on ihe condition of an individual, weather 
conditions, orientation of flight, and flight dura¬ 
tion on any given night; they predicted it could 
take up to 40 days for an individual to travel 
between the Gulf Coast of Louisiana and its 
Canadian breeding areas. 
Estimates of migration duration for passerines 
have largely been based on extrapolations from 
banding recoveries of birds en route (Ellegren 
1993. Fransson 1995. Newton 2008. Yohannes et 
al. 2009) rather than documented departure and 
arrival dates of individual birds from wintering 
and breeding areas. However, given potential 
differences in rates of migration along different 
portions of the route (Stutchbury et al. 2011). 
duration estimates for banded birds are best 
obtained over die complete migration (Fransson 
1995, Yohannes et al. 2009). New technologies, 
such as geolocators, now enable researchers to 
describe the location and duration of migration for 
individual birds (Stutchbury et al. 2009. 2011; 
Bachler ct al. 2010, Robinson et al. 2010. Bridge 
ct al. 2011. Heckscher et aJ. 2011. Ryder et al. 
2011). Use of these techniques is currently limited 
to species larger than small passerines and, even 
as the weight of geolocators continues to decrease, 
their use must be carefully evaluated for imperiled 
species. Only in rare cases can we estimate 
duration of an individual’s migration based on 
observations of birds with unique color-band 
combinations at the beginning and ending of 
migration. 
We report empirical estimates of the duration of 
spring migration for uniquely color-bunded indi¬ 
vidual Kirtland's Warblers {Setophaga kirtlandii) 
observed in the field at the beginning and ending 
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