Protein loss during long-distance migratory flight in passerine birds: adaptation and constraint
Regine Schwilch1,2,
Alessandra Grattarola3,
Fernando Spina3 and
Lukas Jenni1,*
1 Swiss Ornithological Institute, CH-6204 Sempach, Switzerland,
2 Zoological Institute, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland and
3 Istituto Nazionale per la Fauna Selvatica, Via Ca’ Fornacetta 9, I-40064 Ozzano Emilia (BO), Italy
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Fig. 1. Mean lean dry mass (± S.D.) of different organs in birds from Ventotene, after a long-distance flight, and from Switzerland, after only short migratory movements. Bm, breast muscles; H, heart; L, liver; I, intestine; G, gizzard; K, kidney; Lm, leg muscles. Organs that take up a significantly (P<0.05) smaller proportion of total lean dry mass in Ventotene birds than in Swiss birds are marked with an asterisk (compositional analysis).
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Fig. 2. Relationship between total lean dry mass and fat content in birds after a long-distance flight (Ventotene sample). Fat content was calculated as a percentage of total dry body mass. Regressions were significant in all species except the garden warbler (N=6). In the willow warbler, the length of primary 8 also explained some variability in lean dry body mass. Regression lines and sample sizes are as follows: pied flycatcher, y=2.476+0.326lnx1 (r2adj=0.86, P<0.001, N=9); willow warbler, y=0.641+0.082lnx1+0.027x2 (r2adj=0.52, P=0.002, N=17); barn swallow, y=4.030+0.320lnx1 (r2adj=0.56, P=0.013, N=9), where y is lean dry body mass (g), x1 is the amount of fat as a percentage of total dry mass and x2 is the length of primary 8 (mm).
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Fig. 3. Relationship between the ratios of the masses of different organs and total lean dry mass in pied flycatchers (N=10) and willow warblers (N=18) after a long-distance flight. Nutritional organs/exercise organs=lean dry mass of intestine and liver divided by lean dry mass of breast muscles and heart. In the pied flycatchers, the length of primary 8 also explained some of the variability in the ratio breast muscles/leg muscles. Regression lines are as follows: (A) y1=–0.059+0.126x1 (r2adj=0.335, P=0.046); (B) y2=8.400+2.899x1–0.170x2 (r2adj=0.898, P=0.001); (C) y1=1.130–0.349x1 (r2adj=0.382, P=0.003); (D) y2=1.333+1.671x1 (r2adj=0.301, P=0.011), where y1 is nutritional organs/exercise organs, y2 is breast muscles/leg muscles, x1 is the total lean dry mass (g) and x2 is the length of primary 8 (mm).
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Fig. 4. Breast muscle mass (lean dry mass) versus total body mass (fresh mass) in birds after a long-distance flight. Pied flycatcher, y=–0.102+0.056x (r2adj=0.880, P<0.001, N=10); willow warbler, y=0.058+0.038x (r2adj=0.630, P<0.001, N=17); garden warbler, y=0.108+0.037x (r2adj=0.724, P=0.020, N=6); barn swallow, y=–0.538+0.084x (r2adj=0.806, P<0.001, N=9), where x is total body mass (g) and y is lean dry breast muscle mass (g). The length of primary 8 had no significant effect on the relationships between breast muscle mass and total body mass.
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Fig. 5. Relationship between maximum potential vertical flight speed and relative fat load in pied flycatchers (N=10) and willow warblers (N=17) after a long-distance flight. For further explanation and statistics, see Materials and methods and Table 2.
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