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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 3, September 2011 
TABLE 5. Flight capacity estimates based on birds captured in the Sierra de Los Tuxtlas, Mexico presenting mean 
mass of zero fat score birds, sample sizes and standard deviations, estimated fat. and maximum hours and distances possible 
assuming all mass greater than the average when fat score is zero is fuel that could be used for migration. 
Species 
Tuxtlas zero fal 
score f n. SD) 
Estimated 
fat (g) 
Maximum hr* 
of flight 
Maximum flight 
distance (km) 
Empidonax spp. 
10.81 
(12, 1.09) 
1.02 
6.85 
279 
Gray-cheeked Thrush 
24.50 
(5, 2.81) 
2.63 
7.86 
320 
Swainson’s Thrush 
26.84 
(16. 2.13) 
3.95 
10.44 
425 
Wood Thrush 
42.29 
(13. 4.81) 
5.25 
9.09 
370 
Gray Catbird 
34.39 
(7, 2.70) 
0.70 
1.63 
66 
Magnolia Warbler 
7.64 
(7, 0.85) 
0.34 
3.38 
138 
Kentucky Warbler 
11.99 
(37. 0.85) 
1.39 
8.27 
337 
Hooded Warbler 
9.52 
(28. 0.68) 
1.08 
8.07 
328 
Worm-eating Warbler 
11.86 
(8. 1.00) 
1.76 
10.30 
419 
Yellow-breasted Chat 
23.00 
(1. n/a) 
3.38 
10.39 
423 
Ovenbird 
17.59 
(21. 2.09) 
0.96 
4.16 
169 
Painted Bunting 
15.44 
(4. 0.71) 
0.37 
1.87 
76 
Indigo Bunting 
13.66 
(33, 1.24) 
1.51 
7.95 
324 
mands on migrating birds, but it did not appear to 
prevent net fuel gains at this site; examination of 
the percentage of individuals molting in a species 
versus the estimated diel mass gain showed no 
relationship (not shown). 
Spring vs. Autumn .—Sandberg (1996) and 
Sandberg and Moore (1996) hypothesized that 
resource uncertainty and the impending breeding 
season would cause spring migrants to fatten more 
dramatically during migration through more 
northern latitudes than in autumn. Winker 
(1995a) proposed this same pattern might be 
found at the Los Tuxtlas stopover site. However, 
the percentage of species with significant refucl- 
estimated percent of mass (based on l 7, ! ° VC fat ' free mass (estimated from Odum in Dunning 1993)' 
the seven migrant species ihou/in * fr ° m Table 1 ] gdmcd durin ? 'be day in the Sierra de Los Tuxtlas. Mexico f 
■grant spec.es showing significant positive increases in body condition (r = 0.675, P = 0.023). 
