William A. Calder

Microhabitat Selection During Nesting of Hummingbirds in the Rocky Mountains

The importance of nest location in reducing heat loss by radiation and convection is indicated by a preliminary examination of the nest sites of Broad—tailed and Calliope hummingbirds with regard to chilling nights in the Rocky Mountains. Radiation losses are estimated from surface temperatures. Nest diameter and weight increase as a function of time in the nesting season. See full-text article at JSTOR

Respiratory and Heart Rates of Birds at Rest

The respiratory rates of birds are inversely related to their body weights (Groebbels 1932; Salt and Zeuthen 1960). Odum (1945) noted that birds breathe at lower frequencies than do mammals of similar weights. Neither of these observations has been expressed quantitatively. The respiratory and heart rates of mammals can be predicted from empirical equations given by Adolph (1949) and Stahl (1967) which express the resting rates as functions of body weight. The utility of comparable equations for birds prompted the collection and analysis of appropriate data. Data on respiratory and heart rates were obtained from the literature and from additional obser-

Hypothermia of Broad-Tailed Hummingbirds during Incubation in Nature with Ecological Correlations.

The first continuous recordings of natural hypothermia, and the only evidences of hypothermia during incubation, were obtained from temperature sensors embedded in synthetic hummingbird eggs placed in the nests. Resorting to this energy-conserving process was infrequent and could be correlated with reduced opportunity for energy intake.

The Integration of Osmoregulation and Energy Balance in Hummingbirds

Hummingbirds subsist almost entirely on a liquid diet composed of floral nectar, and, when energy demands are high, they can consume more than three times their body mass in fluid per day. At the same time, however, the hummingbirds high metabolism requires efficient extraction of energy and nutrients from a dilute food source that is passing rapidly through the gastrointestinal (GI) tract. The ability of the hummingbird to efficiently process and excrete such large volumes of water must surely entail structural or functional specializations of the kidney and GI tract. The rate of waterflux and nutrient extraction efficiency are also influenced, however, by the animals feeding behavior. Because meal size affects the passage rate of food through the digestive tract (and, therefore, assimilation efficiency), feeding frequency and the amount of nectar consumed per feeding bout will affect the efficiency of nutrient absorption. Ultimately, the water and nutrient content of the nectar produced by the plants should reflect the ability of the hummingbird pollinator to balance its required intake of energy and electrolytes with its ability to excrete the accompanying water load. The simultaneous regulation of water and energy balance in hummingbirds consequently involves the complex integration of renal and intestinal functions and of these physiological processes with behavior and ecology. The hummingbird is a unique animal: its kidney appears to be structurally similar to that of a reptile, but its rate of waterflux is more typical of an amphibian. Nonetheless, it sustains a metabolic level as high as that of any endotherm. The inextricable links among energetics, nutrition, and osmotic regulation in hummingbirds provide a fascinating example of the functional integration of vertebrate organ systems operating at the extreme.

Body size, mortality, and longevity

The body-size dependent relationships of mortality and longevity are examined for birds and eutherian mammals. Differences between mass exponents for maximum recorded longevity and survival times for fractions of original adult populations confirm the age-dependence of mortality in both classes and a size-dependency of population-age distribution. The potential number of offspring produced by a surviving fraction of a mammalian population appears to be a size-independent ecological constant. Social structure would be more likely in larger animals since greater continuity would be provided when a higher proportion of the population consisted of senior, experienced animals, as described by the ratio of time for survival of 1 in 1000 to maximum potential lifespan: t0.001/tmax = 0.91 m0.32/2.94 m0.20 = 0.31 m0.12, that is, the expected lifespan approaches the maximum as size increases.

Sodium, Potassium, and Chloride in Floral Nectars: Energy‐Free Contributions to Refractive Index and Salt Balance

Covich, A. P. 1976. Analyzing shapes of foraging areas: some ecological and economic theories. Annual Review of Ecology and Systematics 7:235-257. Crank, J. 1970. The mathematics of diffusion. Oxford University Press, Oxford, England. l)e Vita, J., D. Kelly, and S. Payne. 1982. Arthropod encounter rate: a null model based on random motion. American Naturalist 119:499-510. Hamilton, W. J., and K. E. F. Watt. 1970. Refuging. Annual Review of Ecology and Systematics 1:263-286. Horn, H. S. 1968. The adaptive significance of coloniality in the Brewers Blackbird (Eiiphagus (vnalocepIhllos). Ecology 49:682-694. Lack, 1). 1972. Ecological adaptations for breeding in birds. Chapman and Hall, London, England. Newton, 1. 1979. Population ecology of raptors. Buteo Books, Vermillion, South Dakota, USA. Orians, G. H., and N. E. Pearson. 1979. On the theory of central place foraging. Pages 155-177 i/l D. H. Horn, G. R. Stairs, and R. D. Mitchell, editors. Analysis of ecological systems. Ohio State University Press, Columbus, Ohio, USA. Poole, R. W., and B. J. Rathcke. 1979. Regularity, randomness, and aggregation in flowering phenologies. Science 203:470-47 1. Post, W. 1974. Functional analysis of space-related behavior in the Seaside Sparrow. Ecology 55:564-575. Pyke, G. H., H. R. Pulliam, and E. L. Charnov. 1977. Optimal foraging theory: a selective review of theory and tests. Quarterly Review of Biology 52:137-154. Rohlf, F. J., and R. R. Sokal. 1969. Statistical tables. W. H. Freeman, San Francisco, California, USA. Schoener, T. W. 1974. Theory of feeding strategies. Annual Review of Ecology and Systematics 2:369-404. Sokal, R. R., and F. J. Rohlf. 1969. Biometry. W. H. Freeman, San Francisco, California, USA. Strong, D. R., Jr., L. A. Szyska, and D. S. Simberloff. 1979. Tests of community-wide character displacement against null hypotheses. Evolution 33:897-913. Werner, E. E., and G. G. Mittelbach. 1981. Optimal foraging: field tests of diet choice and habitat switching. American Zoologist 21:813-829. Zach, R., and J. B. Falls. 1979. Foraging and territoriality of male Ovenbirds (Aves: Parulidae) in a heterogeneous habitat. Journal of Animal Ecology 48:33-52.

Temperature Relationships and Nesting of the Calliope Hummingbird

This is a consequence of the inverse relationship of surface/volume ratio to body mass (Mo.67/M1.? = M-0.33) and of thermal conductance to body mass (M-0.5; Herreid and Kessel 1967; Lasiewski et al. 1967). When the climate becomes inhospitable, the smallest mammals, shrews, can retreat to moderate subsurface microclimates beneath logs, rocks, and in underground burrows. Comparably small birds are not fossorial and hence are exposed to more variable and extreme conditions. This is

Nectar Feeding, Diuresis, and Electrolyte Replacement of Hummingbirds

Hummingbirds depend on floral nectars for energy. This entails a significant water excess which is eliminated in chronic diuresis. In the eight species from which we obtained urine samples, solutes were conserved by reducing urine osmotic concentrations to approximately one-fifth of plasma levels. Sodium and potassium salts accounted for one-half to one-third of the osmotic concentration of urine. These salts can be replaced mostly from trace amounts in the floral nectars. Data from field, laboratory, and the literature are combined to account for salt and water exchanges of broad-tailed and rufous hummingbirds. Published accounts of avian renal morphology and physiology are consistent with hummingbird urinalysis.

On the temperature-dependency of optimal nectar concentrations for birds☆

Abstract In addition to the crucial need for energy balance, the metabolically-intense hummingbirds must maintain osmotic homeostasis by regulating salt and fluid balance. Hypothetically, flowers which have coevolved with pollination by hummingbirds could provide both energy and water balance simultaneously if they produced nectars of appropriate concentrations which depend upon environmental temperature. To the extent that this has not completely adjusted, hummingbirds exposed to cold and hot extremes in temperature will have problems of water excess or deficiency, respectively.

An allometric approach to population cycles of mammals

Abstract The periodic cycles in populations of microtine rodents (3–4 years) and hares (8–10 years) have been treated separately in the past. Attempts to explain them have centered on exogenous factors. Considered together, they provide the suggestion that the natural period is endogenous and size-dependent, and may be a consequence of the physiological and reproductive pace of the life cycle that scales as the fourth root of body mass.