Food limitation is generally thought to underlie much of the variation in life history traits of birds. I examined variation and covariation of life history traits of 123 North American Passeriformes and Piciformes in relation to nest sites, nest predation, and foraging sites to examine the possible roles of these ecological factors in life history evolution of birds. Annual fecundity was strongly inversely related to adult survivaI, even when phylogenetic effects were controlled. Only a little of the variation in fecundity and survival was related to foraging sites, whereas these traits varied strongly among nest sites. Interspecific differences in nest predation were correlated with much of the variation in life history traits among nest sites, although energy trade-offs with covarying traits also may account for some variation. For example, increased nest predation is associated with a shortened nestling period and both are associated with more broods per year, but number of broods is inversely correlated with clutch size, possibly due to an energy trade-off. Number of broods was much more strongly correlated with annual fecundity and adult survival among species than was clutch size, suggesting that clutch size may not be the primary fecundity trait on which selection is acting. Ultimately, food limitation may cause trade-offs between annual fecundity and adult survival, but differences among species in tecundity and adult survival may not be explained by differences in food abundance and instead represent differing tactics for partitioning similar levels of food limitation. Variation in fecundity and adult survival is more clearly organized by nest sites and more closely correlated with nest predation; species that use nest sites with greater nest predation have shorter nestling periods and more broods, yielding higher fecundity, which in turn is associated with reduced adult survival. Fecundity also varied with migratory tendencies; short-distance migrants had more broods and greater fecundity than did neotropical migrants and residents using similar nest sites. HowevEr, migratory tendencies and habitat use were confounded, making separation of these two effects difficult. Nonetheless, the conventional view that neotropical migrants have fewer broods than residents was not supported when nest site effects were controlled

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Avian Life History Evolution in Relation to Nest Sites, Nest Predation, and Food

Life history theory predicts that parents should value their own survival over that of their offspring in species with a higher probability of adult survival and fewer offspring. We report that Southern Hemisphere birds have higher adult survival and smaller clutch sizes than Northern Hemisphere birds. We subsequently manipulated predation risk to adults versus offspring in 10 species that were paired between North and South America on the basis of phylogeny and ecology. As predicted, southern parents responded more strongly to reduce mortality risk to themselves even at a cost to their offspring, whereas northern parents responded more strongly to reduce risk to their offspring even at greater risk to themselves.

https://science.sciencemag.org/content/sci/292/5516/494.full.pdf

Fecundity-Survival Trade-Offs and Parental Risk-Taking in Birds

ity in driving life history evolution (e.g., Cole 1954, Murphy 1968, Charlesworth 1980, Reznick and Bryga 1987, Curio 1989, Reznick et al. 1990). Yet, food is thought to be more important in birds (Lack 1948, 1968, Murphy and Haukioja 1986, Martin 1987). Nest predation is a theoretical alternative to food limitation (Slagsvold 1982, Lima 1987, Martin 1992) and recent evidence suggests that nest predation may exert a greater influence on life history evolution than previously thought (Slagsvold 1982, Martin 1993a, b, 1995, Martin and Clobert 1996, McCleery et al. 1996). However, nest predation may often interact with food limitation to influence life history traits (Lima 1987, Martin 1992, 1995). These contrasting and interacting roles of food limitation versus mortality (nest predation) make birds an intriguing system for examining ecological and evolutionary causes of life history variation.

Life history evolution in tropical and south temperate birds : What do we really know ?

We re—examined the longstanding dogma that cavity—nesting birds have larger clutch sizes than open—nesting species because of lower nest predation rates, which allow longer developmental periods. We provide data on nesting success of open—nesting species plus excavator and nonexcavator species (cavity—nesters that do vs. do not create their own cavities) of birds that coexist in the same habitat and use natural nest sites; studies were conducted in central Arizona in high—elevation forest drainages from 1987 to 1989. In comparisons among species, nest success increased in the order open—nesting < nonexcavator ° excavator species. Length of the nestling period increased, whereas number of broods decreased, with increased nest success across these nest types. Contrary to conventional expectation, clutch size did not increase directly with increased nest success and length of the nestling period, and these patterns were not simply a result of phylogenetic effects. A literature review of data on adult survival in land birds indicated that nonexcavators have significantly lower adult survival than the other two nest types. The lower adult survival of nonexcavators was associated with greater annual productivity than for the other two nest types. Annual productivity appeared to be associated with nest site attributes, whereas number of broad attempts was related to nest failure rate. Clutch size was a byproduct of annual productivity and number of brood attempts. Thus, the long—standing paradigm relating clutch size directly to nesting failure and developmental period was not supported.

https://www.jstor.org/stable/pdfplus/1940764.pdf

Life History Traits of Open- vs. Cavity-Nesting Birds

The relationship between fleshy-fruited plants and their vertebrate seed dispersal agents often has been depicted as subject to important interannual variation, but no study has thus far documented such variation on a long-term basis. This paper presents the results of a 12-yr investigation on fleshy-fruited plants and avian frugivores in a Mediterranean montane locality of southeastern Spain. The main objective was to document patterns and correlates of long-term vari- ation in the composition and abundance of fruits and birds, with particular reference to seed dis- persers. During October-December (''autumn'' period) 1978-1990, abundance of ripe fruits and birds was assessed in a 4-ha plot in dense, well-preserved sclerophyllous scrub, by means of counts in permanent plots and mist-netting, respectively. Diet composition and fruit preference patterns of Erithacus rubecula and Sylvia atricapilla, the two most abundant seed dispersers, were also inves- tigated over the same period, using fecal sample analyses. Possible consequences to the birds of annual variation in fruit supply and diet composition were investigated using data on fat deposition levels and recapture rates of mist-netted individuals. Total fruit abundance (i.e., mean ripe fruit density of all species combined) fluctuated among years between 5.4 6 11.1 fruits/m 2 (mean 6 1 SD; 1986) and 77.1 6 78.0 fruits/m 2 (1989) and was positively related to the amount of rainfall in the preceding spring. Not all fruiting species bore ripe fruits every year, and among those species that did, fruit density fluctuated asynchronously and to variable degrees. Seven out of 13 species exhibited significant supra-annual periodicity in fruit abundance, with fluctuation periods ranging from 2 to 6 yr. Variation in the abundance of each of the six most abundant fruit species was unrelated to annual variation in rainfall. The autumn bird assemblage at the study site was made up of year-round resident species (54.1% of captures, all years combined) that were largely fruit predators (feeding on pulp or seeds without performing dispersal) and of autumn-winter resident species (45.5% of captures) that were largely seed dis- persers. Bird abundance, all species combined, ranged between 27.1 and 61.5 captures/100 net-hours for 1987 and 1986, respectively. Depending on year, seed dispersers made up 25.6-75.4% of the total captures, and fruit predators made up 20.9-69.7%. The relative importance of nonfrugivores was always negligible (1.1-9.9%). No correlation existed across years between total fruit abundance and the capture rates of all bird species combined, seed dispersers, or fruit predators. Annual variation in the abundance of seed dispersers was positively related to November mean maximum temperature. At the individual species level, S. atricapilla capture rates were correlated with the abundance of the fruits of Phillyrea latifolia, a species exhibiting extreme annual fluctuations. Annual variation in the importance of fruits in the diet of S. atricapilla and E. rubecula was not significantly related to changes in fruit abundance. Composition of the fruit diet of these species fluctuated markedly among years, and there was little agreement between composition of the diet and of the fruit supply. Certain fruit species were significantly preferred, and others avoided, by both S. atricapilla and E. rubecula. Ranking of interspecific fruit preferences remained consistent among years and was related to differences in carbohydrate and lipid content of fruit pulp. Fat deposition levels of S. atricapilla and E. rubecula did not vary among years and were not significantly related to fruit abundance, percentage of fruit volume in the diet, or contribution of lipid-rich fruits to the diet. Return rates of individuals of these species to the study locality in successive wintering periods were very low, and not significantly related to diet composition or fruit abundance. Prevalence of abiotic over biotic determinants of annual variations, extensive decoupling of the long-term temporal dynamics of fruits and dispersers, and the remarkable ''indifference'' of frugivores to variations in the fruit supply all point to the non-equilibrial nature of this assemblage of fleshy- fruited plants and their avian dispersers.

Long-term dynamics of mediterranean frugivorousbirds and fleshy fruits: a 12-year study

Survival rates of tropical forest birds are widely assumed to be high relative to the survival rates of temperate forest birds. Much life-history theory is based on this assumption despite the lack of empirical data to support it. We provide the first detailed comparison of survival rates of tropical and temperate forest birds based on extensive data bases and modern capture-recapture models. We find no support for the conventional wisdom. Because clutch size is only one component of reproductive rate, the frequently assumed, simple association between clutch size and adult survival rates should not necessarily be expected. Our results emphasize the need to consider components of fecundity in addition to clutch size when comparing the life histories of tropical and temperate birds and suggest similar considerations in the development of vertebrate life-history theory.

M. K. Klimkiewicz

Papers

Survival rates of birds of tropical and temperate forests: will the dogma survive?