In this study, we investigate whether a tissue-level constraint can explain the general inverse relationship between growth rate and precocity of development in birds. On the whole, altricial (dependent) chicks grow three to four times faster than the less dependent, more able chicks of precocial species of similar adult mass. We suggest that an antagonism between growth and acquisition of mature function in skeletal muscle constrains postnatal growth and development in most species of birds. Altricial species, represented by European starlings in this study, hatch with skeletal muscle having low capacity for generating force but grow rapidly. Conversely, precocial species (northern bobwhite quail and Japanese quail), hatch with relatively mature skeletal muscle, especially in their legs, but grow more slowly. As development proceeds in all species, exponential growth rates decrease as muscles acquire adult levels of function. Among four variables associated with muscle function, exponential growth rate (EGR) was negatively correlated with pyruvate kinase activity (glycolysis), potassium concentration (electrical potential), and dry weight fraction (contractile proteins) in both pectoral and leg muscles but not with citrate synthase activity (aerobic metabolism) in either set of muscles. For pectoral muscle, these variables accounted for 87% of the total variation in EGR in all three species combined despite a twofold difference in growth rates between the starling and quail. EGRs of leg muscle (51% of variation accounted for) were less than predicted by the pectoral-muscle equation in quail during the early part of the postnatal period and in starlings during the late postnatal period. This result would not contradict a growth rate/maturity constraint hypothesis if EGRs were down-regulated for allometric or other considerations.

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We estimated annual survival from proportions of first-year and older birds in museum collections of several species of North American and Neotropical passerine birds (Order Passeriformes). The quality of estimates of survival from museum specimens depends on accurate aging, usually based on plumage markers, and unbiased collecting. The advantages of an age-ratio approach are broad temporal and geographic sampling, large sample sizes, reduced bias from adult dispersal, and access to species and areas not readily sampled in mark-recapture studies. Biases in estimated survival due to sex-and agebased biases in collecting are discussed in detail. Survival estimates were higher in tropical compared to temperate populations/species in Pyrocephalus, Icterus, Pheucticus, and Cyanocompsa, but not Catharus. In seven of nine North American species, estimates of survival from museum collections exceeded those obtained in local MAPS mark-recapture studies. Generalizations concerning adult survival rates in natural populations continue to be elusive, but the use of a variety of estimation approaches will enrich the empirical database and strengthen confidence in perceived patterns of life-history traits.Zusammenfassung Wir haben die jährlichen Ü berlebenswahrscheinlichkeiten von mehreren Arten nordamerikanischer und neotropischer Sperlingsvögel (Ordnung Passeriformes) aus dem Zahlenverhältnis von 1-jährigen zu älteren Vögeln in Museumssammlungen abgeschätzt. Die Verlässlichkeit der Schätzung von Ü berlebensraten aus Museumsbälgen hängt von der genauen Altersbestimmung ab, die meist auf Gefiedermerkmalen beruhen, und der Zufälligkeit des Sammelns. Vorteile der AltersklassenMethode sind ihre breite geografische und zeitliche Anwendbarkeit, hohe Probenzahlen, reduzierter Einfluss der Wanderung adulter Tiere sowie Anwendbarkeit auf Arten oder Gebiete, bei denen Fang-Wiederfang-Studien nicht gut anwendbar sind. Erwartete Fehler bei der Schätzung durch geschlechts-oder alters-abhängiges Sammeln werden ausführlich diskutiert. Die gefundenen Ü berlebensraten waren höher in tropischen als in temperaten Populationen bzw. Arten von Pyrocephalus, Icterus, Pheucticus und Cyanocompsa, nicht aber bei Catharus. In sieben von neun nordamerikanischen Arten waren die mit der AltersklassenMethode geschätzten Ü berlebensraten höher als die aus lokalen MAPS Fang-Wiederfang-Studien. Allgemein gültige Aussagen zu Ü berlebenswahrscheinlichkeiten in natürlichen Vogelpopulationen sind mangels weiterhin schwierig. Die Anwendung verschiedener Schätzmethoden bietet die Möglichkeit, die empirische Datengrundlage zu verbreitern und damit life-history-Vergleiche auf eine bessere Grundlagen zu stellen.R. E. Shea: Deceased.Communicated by F. Bairlein.