Charles R. Blem

Energetics of nestling house sparrows Passer domesticus.

Abstract 1. Energy utilization of nestling house sparrows, Passer domesticus, during growth and development, is partitioned by means of measurements of resting metabolism, caloric content of the carcass, and metabolized energy. 2. Caloric content per g of fresh tissue decreases from day 1 through day 3 of development, then increases progressively thereafter as a result of increased lipid and decreased water content. 3. Daily increases in caloric content of the carcass (production) range from 1·6 kcal (day 1) to 3·8 kcal (day 5), and the average daily increase is 2·9 kcal. 4. Weight-specific resting metabolism at 36°C increases from hatching through the 10th day of development. 5. Metabolized energy and gross energy intake reach a maximum at about the 13th day of nestling development and decrease in older nestlings. 6. Efficiency of energy utilization is lowest in 1- to 3-day-old nestlings (55·7–58·5%), increases thereafter and approximates adult levels (67·1–70·2%) before fledging. 7. Ratios of production/metabolized energy and production/gross energy intake are highest during the first 5 days of development and decrease with age of the nestling. 8. Over the entire developmental period, 290·1 kcal are ingested by each nestling, of which 199·2 kcal (68·7%) is metabolized and the rest (90·0 kcal) excreted; the metabolized energy can then be partitioned into resting metabolism (113·4 kcal), cost of activity (47·4 kcal) and caloric content of the carcass (38·4 kcal).

RUFOUS HUMMINGBIRD SUCROSE PREFERENCE: PRECISION OF SELECTION VARIES WITH CONCENTRATION

Abstract We tested concentration preferences of Rufous Hummingbirds (Selasphorus rufus) offered sucrose solutions in small feeders in the field. When sucrose solutions differing in increments of 10%, from 10% to 70%, were presented simultaneously, hummingbirds preferred 50% to higher and lower concentrations. They did not show a significant preference in the range from 50% to 70% . When options were offered in pairs of choices differing from 1–25%, hummingbirds demonstrated statistically significant preferences that varied with mean concentration in a curvilinear manner. At concentrations approximating those of hummingbird-pollinated flowers (20%), hummingbirds showed greatest specificity and could distinguish solutions differing by only 1%. At concentrations above and below 20%, greater differences between choices were required to elicit significant preferences.

Metabolic adaptation to local climate in birds

Abstract 1. 1. Existence metabolism in house sparrows, Passer domesticus, collected at nine North American localities, varies inversely with mean mid-winter and mid-summer temperatures of collection sites at rates of 0 · 0036 and 0 . 0041 kcal g−1 day−1°C−1, respectively. 2. 2. Behavioral responses and improved insulation during the winter provide further adaptation to cold climates at rates of 0.0019 and 0.00012 kcal g−1 day −1 °C−1, respectively. 3. 3. Within the range of collection sites, ultimate minimal existence metabolism decreases southward, while upper critical temperatures predicted from these values increase. 4. 4. Ultimate maximum existence metabolism and lower limits of temperature tolerance increase northward with drop in winter temperature and constitute the critical metabolic characteristics that enable the species to be permanent residents at the collection sites. 5. 5. Maximum and minimum existence energy values and ultimate lower limits of temperature tolerance are used to construct a graphic physiological model for the distribution of house sparrows in North America.

Geographic variation of thermal conductance in the house sparrow (Passer domesticus)

Abstract 1. 1. Thermal conductance as assessed from cooling rates of carcasses of the house sparrow. Passer domesticus , is inversely related to latitude and isophane in North America. 2. 2. No significant difference in heat loss between sexes could be detected. 3. 3. Weight-specific thermal conductance varies inversely with body weight, but the slope of the equation for this relationship for southern localities is greater than that of northern localities. 4. 4. Conductance per unit surface area is linearly related to body weight in southern samples, but does not vary significantly with weight in northern samples. 5. 5. Heat loss per bird is a function of body weight within northern samples, but does not vary with weight in southern samples.

Geographic Variation in Mid-Winter Body Composition of Starlings

-Starlings (Sturnus vulgaris) collected during mid-winter from a 2,800-km longitudinal range in the eastern United States showed significant geographic variation in body weight, feather weight, wing length, culmen length, tarsus length, dry weight, lean dry weight, lipid weight and lipid index. Total lipid reserves and indices were greatest at middle latitudes. Starlings from the central part of the study area were significantly larger than those at either northern or southern extremes as measured by wing length, body weight and lean dry weight. Insulation, as measured by weight of body feathers per unit of surface area, increased with isophane, an index of regional temperature, but morphometric measures were generally less interpretable. Geographic variation within a species generally reflects ecotypic adaptation or phenotypic response to differences in environment. Earlier in this century, the morphometric aspects of such variation received much attention partly because of the ease of measurement, availability of museum specimens, and also because the theme of most research was systematic or taxonomic rather than physiological or ecological. In the past two decades, biologists have increasingly paid attention to the functional and adaptive significance of geographic variation. However, the analyses seldom have provided data useful in the study of the relationships among morphology, physiology and environmental conditions. To date, studies of the relationships between variation in body composition and environment in endothermic animals are rare, have dealt entirely with sedentary species, and have produced differing results. Hayward (1965), in an analysis of six geographic races of North American deer mice (Peromyscus), found large individual and interracial variability in body fat, but discerned no regular interlocality variation in any gross component of body composition either in winter or summer. Blem (1973, 1974), working with North American House Sparrows (Passer domesticus), demonstrated regular geographic variation in several body components and insulation, which appeared to be related to mid-winter temperature and adaptive for winter survival. Although numerous studies of seasonal differences in body composition or geographic variation in metabolism are available (e.g., see Hudson and Kimzey 1966, Helms et al. 1967, Barnett 1970), few other data reflect upon geographic variation in body composition or energy reserves. I studied the mid-winter body composition of a partially migratory species, the Starling (Sturnus vulgaris). In eastern North America, individual Starlings may migrate several hundred kilometers along a generally north-south axis, but resident flocks are found throughout the range sampled in the present study (see Kessel 1953). Although migratory individuals cannot be distinguished from non-migrants, I know of no evidence that mid-winter populations are moving great distances (if at all) in response to weather extremes. Therefore my working hypothesis was that interlocality variation at least partially reflects adaptation for survival of mid-winter environment at the collec-

Mid-winter lipid reserves of the golden-crowned kinglet

Passerine birds have relatively high weight-specific metabolic rates that increase sharply in progressively smaller species (Lasiewski and Dawson 1967). Kendeigh (1970) pointed out that small birds generally are poorly insulated and might be expected to be stressed by low ambient temperature. He suggested, therefore, that energy expenditure may be influential in determining the lower limits of body size of passerines (Kendeigh 1972, but see Kendeigh et al. 1977). High costs of endothermic temperature regulation may be avoided through overnight decreases in body temperature; it appears that nocturnal hypothermia may naturally occur in several species of small passerines (Haftorn 1972, Chaplin 1976, Bucher and Worthington 1982, Lustick et al. 1982). Direct proof is difficult to obtain; hypothermia may occur in small birds in the laboratory because of stress from caging or handling, and may not be a natural part of the daily cycle. Kinglets (Regulus spp.) might be expected to show hypothermia because they are among the smallest Temperate-Zone passerines in the world (see Kendeigh 1972, Chaplin 1982). Two species occur in North America, the Golden-crowned Kinglet (R. satrapa; body weight 5.7 g) and the Ruby-crowned Kinglet (R. calendula; 6.3 g; Kendeigh 1972). These species appear to tolerate cold and may winter as far north as southern Canada and Alaska. To our knowledge, little has been published about the utilization or storage of energy by kinglets (see Gavrilov 1972). Therefore, we undertook to measure the size of lipid depots and the amplitude of daily energy cycles in the Golden-crowned Kinglet. We hypothesized that such a bird might not be able to carry sufficient energy stores to maintain high body temperatures over long, cold, winter nights. If daily cycles of energy storage are not sufficient to fuel overnight survival, this indicates that nocturnal hypothermia must occur if the species is to survive.

The Eastern Cottonmouth (Agkistrodon piscivorus) at the Northern Edge of its Range

The northernmost population of the eastern cottonmouth (Agkistrodon piscivorus) is in Virginia near Hopewell at the confluence of the James and Appomattox rivers. Female cottonmouths there produce relatively large litters and attain sexual maturity at sizes greater than reported elsewhere. Meristic characters of the northernmost population differ only slightly or not at all from neighboring populations in southeastern Virginia or northeastern North Carolina, but melanism increases significantly southward. Vitellogenesis, ovulation, and birth in the northernmost population appear to occur several weeks later than in southern populations. Most small cottonmouths did not survive cold winters and few individuals less than 600 mm snout-vent length were observed; thus the population is comprised largely of older snakes (>4 yr). Most mature females (91.7%) reproduced annually. Winter mortality in hibernacula may be an important limiting factor in this northernmost population of cottonmouths.

Estimation of Body Mass of Voles from Crania in Short-Eared Owl Pellets

-Voles comprised more than 95% of the diet of short-eared owls (Asio fammeus) breeding in western Montana. Regression analyses were used to estimate body mass of meadow voles (Microtus pennsylvanicus) and montane voles (M. montanus) from measurements of crania found in pellets of these owls. Most voles eaten by the owls were in a size class typical of subadults, and only a few adult voles were eaten. Mean body mass of the two species of voles appearing as prey items in pellets did not differ significantly. Body mass estimated from cranial dimensions by regression is superior to the common practice of assuming that all prey items are adults, or to calculation of mass from single skeletal measurements.

The energetics of young Japanese quail, Coturnix coturnix japonica

1. 1. Measurements of metabolized energy, resting metabolism and caloric content of the body are used to partition the energy utilization of young Japanese quail, Coturnix coturnix japonica, during growth and development. 2. 2. Metabolized energy (ME) in kcal/bird-day from the day of hatching through 42 days of age may be accurately predicted as: ME = −1.686 + 0.014% energetic efficiency (wt°-67) − 0.784 age (days) + 2.007 weight change (g) + 1.942 wt°-67. 3. 3. Weight-specific resting metabolism was lowest in newly hatched chicks and highest in one-week-old chicks. 4. 4. Production averaged 3.5kcal/day and greatest rates of production occurred during the middle of the growth period (20–35 days). 5. 5. Activity costs ranged from 2.0 to 5.7 kcal/day, but remained relatively constant around a mean of 4.1 ± 0.2 (S.E.) kcal/day. 6. 6. The efficiency of production varied from 2.5 to 29.1%, and was highest during the middle of the developmental period (day 5 through day 23).

FACTORS ASSOCIATED WITH GROWTH OF NESTLING PROTHONOTARY WARBLERS

Abstract The Prothonotary Warbler (Protonotaria citrea) is the only wood warbler in the eastern United States that nests in cavities. It readily accepts nest boxes in lieu of natural breeding sites and therefore provides an excellent model for tests of ecological factors associated with reproductive success. During 1987, 300 nest boxes were placed along a 30-km transect along the tidal James River in eastern Virginia, and these nest boxes have been monitored every year through 2000. During the 1999 and 2000 breeding seasons, we collected 2910 measurements of nestling mass, and recorded ages of parental females, dates of clutch initiation and hatching, brood sizes, and the number of young that survived to fledging. Multivariate analysis of variance indicates that nestling mass was a significant function of brood size, hatching date, age of the female, and year, even when the effects of all independent variables were considered simultaneously. Growth rate and fledging mass were significantly lower in larger broods. Two- to three-year-old females fledged nestlings with greater mass than one-year-old females and females older than three years. Frequency of handling nestlings was not significantly associated with changes in their mass. Ambient temperature of the study area during the breeding season was significantly colder during 1999 than during 2000. Growth rate, fledging mass, and rate of survival of nestlings to fledging were lower during 1999 than during 2000. Growth of nestling birds was related to a large suite of intrinsic variables, but application of growth data to environmental concerns requires knowledge of both demographic and ecological factors.