Shaw and Winker • SPRING REFUELING IN MIGRANT PASSERINES 
583 
TABLE 6. Total captures, numbers and percent of individuals recaptured > 1 night after initial capture, and numbers 
and percent of individuals recaptured >2 nights after initial capture in the Sierra de Los Tuxtlas, Mexico. 
Species 
Total captures 
Recaptures (n) 
Perccni 
recaptured 
Recaptured after 
48 hrs (n) 
Percent recaptured 
after 48 hrs 
Empidonax spp. 
35 
2 
5.7 
2 
5.7 
Gray-cheeked Thrush 
58 
3 
5.2 
Swainson's Thrush 
323 
20 
6.2 
9 
Wood Thrush 
120 
26 
21.7 
15 
12.5 
Grav Catbird 
38 
1 
2.6 
1 
Magnolia Warbler 
39 
4 
10.3 
4 
10.3 
Kentucky Warbler 
136 
25 
18.4 
22 
16.2 
Hooded Warbler 
171 
42 
24.6 
30 
17.5 
Worm-eating Warbler 
78 
17 
21.8 
12 
15.4 
Yellow-breasted Chat 
43 
3 
7.0 
2 
Ovenbird 
68 
19 
27.9 
14 
20.6 
Painted Bunting 
31 
2 
6.5 
1 
Indigo Bunting 
159 
5 
3.1 
4 
ing was not different between seasons at this site: 
six of II species (55%) in Winker (1995a) and 
seven of 13 species (54%) in this study. Diel 
gains, estimated using identical assumptions 
(Winker 1995a), were remarkably similar among 
species gaining mass at this site, averaging 5.1% 
in autumn (Winker 1995a) versus 5.0% in spring. 
-Species that had significant gains differed be¬ 
tween seasons but, in spring, no species had a net 
loss in condition as occurred on the site during 
autumn (Winker 1995a). 
Winker (1995a) detected no significant diel 
condition increases in Wood Thrushes, Hooded 
Warblers, and Ovenbirds at this site in autumn, 
but each had significant increases at this same site 
during spring. All three of these species winter in 
large numbers in Los Tuxtlas and surrounding 
regions. It is likely that many individuals captured 
in autumn were arriving on or near their wintering 
areas and had no need to refuel. In spring, these 
species are embarking on migration and/or 
arriving from areas to the south, and the need 
for refueling may be greater. However, Gray 
Catbirds also winter at Los Tuxtlas. and Winker 
(1995a) detected significant autumn diel gains in 
this species where none was apparent in spring. 
The reasons for seasonal differences remain 
unclear. 
Route Selection .—Migrants at this site were 
carrying insufficient fuel for long-distance flight. 
Trans-gulf migrants should be expected to dem¬ 
onstrate higher levels of refueling or to remain 
TABLE 7. Flight capacity estimates for average individuals of the study species indicating cost of flight (g of fuel/hr) 
maximum hours possible based on a single day in the Sierra de Los Tuxtlas, Mexico, and estimates for maximum hours and 
distances possible. 
Species 
Flight cost 
(g/hr)‘ 
Hours of flight 
daily gains" 
Gray-cheeked Thrush 
0.33 
NA 
Swainson’s Thrush 
0.38 
2.26 
Wood Thrush 
0.58 
6.33 
Gray Catbird 
0.43 
NA 
Magnolia Warbler 
0.10 
6.34 
Worm-eating Warbler 
0.17 
3.75 
Kentucky Warbler 
0.17 
4.65 
Hooded Warbler 
0.13 
3.26 
Ovenbird 
0.23 
2.55 
Indigo Bunting 
0.18 
NA 
Maximum hrs 
of flight' 
5.78 
17.47 
9.22 
7.66 
9.68 
16.56 
12.04 
17.90 
13.12 
12.83 
Maximum flight 
distance (km) a 
235 
711 
375 
312 
394 
674 
490 
729 
534 
522 
Based on calculations from Tucker (1974). 
Assuming average speed of 40.7 km/hr for an average Swamson s Thrush (Nisbet el al. 1963). 
