Figure 5.5 Maximum fuel deposition rates (FDR, expressed as % lean body mass per day) for populations (upper) and individuals (lower) of free-living migratory birds of different body weights. Data are based on changes in body mass over time (minimum two days), either in individuals or in populations. Only the highest value for a species is included. Maximum FDRs were negatively correlated with body mass, both for individuals and for populations. No significant differences in mass-specific daily FDRs were found between passerines, waders and other non-passerines. Combining all species, the relationship between maximum recorded daily fuel deposition and body mass (BM) for populations is 1.16 BM-035 (r2 = 0.66, P< 0.001, 95% confidence interval (CI) of slope -0.27 to -0.42) and for individuals 2.17 BM-034 (r = 0.54, P< 0.001, 95% CI of slope -0.23 to -0.44). From Lindström (2003), in which the original references may be found.
sex and age groups, according to the journeys they undertake. In this section, I have been concerned primarily with mean rates of weight gain in different populations, and how they vary between species in relation to body size. But within species, rates of weight gain can be enormously variable, as can the fuel loads at departure. These variations, which are due largely to variations in food acquisition, and their influence on the speed of migration, are discussed in Chapter 27.
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