Ewert et al. • KIRTLAND'S WARBLER SPRING MIGRATION 
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F-IG. 1. (A) Approximate breeding and wintering locations of color-banded Kirtland’s Warblers for which we estimated 
duration and distance of spring migration. (B) Breeding locations of color-banded Kirtland's Warblers in the Lower 
Peninsula of Michigan by county. (C) Approximate location of wintering sites sampled on southern Eleuthera, The 
Bahamas (described in Wundcrlc et al. 2010). 
distance traveled/day was calculated by dividing 
Ihe linear distance traveled between wintering and 
breeding areas by the number of nights between 
the last observation of an individual on Eleuthera 
and the first observation of the same bird in 
Michigan. Values for both the maximum duration 
of migration and average distance traveled/day are 
presented as means ± SD. 
RESULTS 
Kirtland’s Warblers were consistently seen on 
lileuthera through late April 2003-2010 (Wun- 
derle et al., unpubl. data) with the latest date in 
any year being 2 May 2006. First arrival dates of 
males reported anywhere in the Lower Peninsula 
‘>1 Michigan ranged from 2 to 7 May during our 
study and the total number of Bahamas-banded 
Kirtland’s Warblers observed in breeding areas 
during the study period in any given year was 7 to 
23 (Table 1). In comparison, mean arrival dates of 
males from 2006 to 2010 ranged from 13 to 22 
May for the warblers at a subset of Kirtland's 
Warbler siles in Michigan’s Lower Peninsula 
(SMR, unpubl. data). 
The estimated mean duration of migration for 
five uniquely color-banded male Kirtland’s War¬ 
blers observed in breeding areas (Fig. 1) was 15.8 
± 4.2 days (Table 2). Four of these five birds 
were observed on the first day the territory was 
checked and the fifth (band # 2221-08906) was 
observed 3 days after the territory was last visited. 
Thus, it is likely the actual mean duration of 
spring migration for these five individuals was 
less than the calculated mean of 15.8 days. The 
mean distance traveled/day, based on this esti¬ 
mated duration, was 144.5 t31.2 km. 
Some observations were not included in our 
calculations of mean duration of migration 
because the birds were found opportunistically, 
and were not detected until relatively late in May 
