A?stract.. The energy budget of nestling Red-winged Blackbirds (Agelaius phoeniceus) was determmed usmg doubly labeled water ( 3 HH 1 SO) to measure field metabolic rate (FMR) and body component data. to me~s~re growt~ energy. Sex-specific measurements permitted the evaluation of the effects of this species substantial sexual size dimorphism on FMR and total energetics. FMR averaged co. re~ease of 5.12 mL·g-1 • h-1 , or 0.129 kJ ·g-1 • h-1 , with no significant differences b~tween the sexes. pay~me FMRs of C0 2 production (5.34 mL·g-1 ·h-1 ) were higher, but not sig-mfic~ntly so, than mghttm1eFMR~ (~.45 mL·g~1 ·h-1 ). Water influx averaged 0.95 mL·g-I.d-', with daytime rate~ (!.22 mL·g '·d-1 ) Significantly higher than nighttime (0.40 mL·g-'·d-1 ) rates.T?tal assimila_ted energy from hatching to fledging was 1014 and 797 kJ for male and female nestlmgs: respectively. The sexual di~erences in total energetics reflected differences in body size of the nestlings and suggest that there IS a greater cost to the parents in raising males than in raising females.

We developed a simulation model of phylogenesis with which we generated a large number of phylogenies and associated data matrices. We examined the characteristics of these and evaluated the success of three taxonomic methods (Wagner parsimony, character compatibility, and UPGMA clustering) as estimators of phylogeny, paying particular attention to the consequences of changes in certain evolutionary assumptions: relative rate of evolution in three different evolutionary contexts (phyletic, parent lineage, and daughter lineage); relative rate of evolution in different directions (novel forward, convergent forward, or reverse); variation of evolutionary rates; and topology of the phylogenetic tree. Except for variation of evolutionary rates, all the evolutionary parameters that we controlled had significant effects on accuracy of phylogenetic reconstructions. Unexpectedly, the topology of the phylogeny was the most important single factor affecting accuracy; some phylogenies are more readily estimated than others for simply historical reasons. We conclude that none of the three estimation methods is very accurate, that the differences in accuracy among them are rather small, and that historical effects (the branching pattern of a phylogeny) may outweigh biological effects in determining the accuracy with which a phylogeny can be reconstructed.

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