Richard E. MacMillen

Threshold Model of Feeding Territoriality and Test with a Hawaiian Honeycreeper

A model is proposed predicting that in nectarivorous birds territorial behavior will occur above a lower threshold of nectar productivity in a foraging area and disappear above an upper threshold. These thresholds are determined by the daily costs of living of territorial and of nonterritorial individuals and by the pressure of competing birds for the resource. Decline of efficiency of territorial exclusiveness is predicted as productivity increases from the lower to the upper threshold. Hawaiian honeycreepers (Vestiaria coccinea) supported the model.

WATER REGULATORY EFFICIENCY IN HETEROMYID RODENTS: A MODEL AND ITS APPLICATION'

We have developed and tested a model of water regulatory efficiency for the rodent family Heteromyidae. The model is based on the premise that granivory coupled with increasing aridity and seasonality of rainfall has been the major theme throughout the evolutionary history of the family; it states further that water regulatory efficiency is negatively correlated with body mass in the family, and that member species are largely dependent upon a common resource packet (seeds) to meet both energy and water needs. A test of the model with five genera and 13 species revealed positive results across the entire family, but the two most speciose genera, Perognathus and Dipod- omnys, showed seemingly conflicting patterns: the smaller (in mass) genus, Perognathus, conformed strongly to the model, while in Dipodomys water regulatory efficiency was fixed at a level equivalent to that of the largest Perognathus spp. (-35-40 g). At this mass in these genera, in addition, occurs the demarcation between strict quadrupedality (Perognathus) and bipedality (Dipodomys), a strict scaling of cheek pouch volume with mass in Perognathus but independence of mass in Dipodomys, and the common use of torpor in Perognatlhus, with its near absence in Dipodomys. We interpret our findings to indicate that initially selection favored a decrease in mass with a concomitant increase in water regulatory efficiency and reduction in absolute energy need in heteromyids, tracking pro- gressive aridity during the Tertiary. In Dipodomys, the option of bipedality was adopted, apparently freeing them from energetic constraints imposed strictly by mass, coupled with an intermediate and fixed level of water regulatory efficiency that dictates use of seeds with high metabolic water yields. The quadrupedal Perognathus have retained a mass-specific water regulatory efficiency, ensuring maintenance of both water and energy balance on a broad array (with respect to protein: lipid: carbohydrate and metabolic water yield) of seeds, when their more-limited locomotor powers are consistent with seed availability; torpor is the tradeoff, enhancing survival during energetically de- manding periods.

Energy metabolism and pulmocutaneous water loss of Australian hopping mice

Abstract 1. 1. Energetically Australian hopping mice are similar to other small desert rodents, utilizing hyperthermia under conditions of high T A , and having reduced basal metabolic rates and very short thermal neutral zones. 2. 2. Patterns of pulmocutaneous water loss resemble those of other small rodents, although rates are somewhat higher than in certain other desert rodents. 3. 3. The energetic responses of Australian hopping mice in and above thermal neutrality appear to reflect very closely the environmental conditions which prevail in their burrows during the daytime.

Oxygen Consumption, Estivation, and Hibernation in the Kangaroo Mouse, Microdipodops pallidus

T HE pallid kangaroo mouse occurs only in the desert parts of western Nevada and extreme eastern California. Its habitat is restricted to areas of fine sand which support some plant growth. Like its relatives, the kangaroo rats (Dipodomys) and the pocket mice (Perognathus), it is nocturnal, fossorial, and gramnivorous and can under some circumstances live indefinitely on a dry diet without drinking water. The general life history (Hall and Linsdale, 1929) of this kangaroo mouse and the details of its distribution (Hall, 1946) are known, but virtually no quantitative data on its physiology are available. The present study was undertaken to compare the thermoregulation of Microdipodops with that of the better-known genera, Dipodomys and Perognathus. These three genera belong to the family Heteromyidae, which has been more successful in occupying the arid parts of western North America than any other group of mammals.

Scaling of Energy Metabolism and Evaporative Water Loss in Heteromyid Rodents

Oxygen consumption (V̇o2), evaporative water loss (ṁwe), and body temperature (Tb) of 117 individuals of 13 species of heteromyid rodents were determined at ambient air temperatures (Ta) of 5, 15, 25, and 35 C; the 13 species encompass all five genera in the family Heteromyidae, cover the range in habitat distribution, and vary in body mass from 8 to 130 g. The relationship between V̇o2 and Ta generally follows the Scholander model in the 13 species, although the three nonxeric species (Heteromys desmarestianus, Liomys irroratus, L. salvini) exhibit a thermoneutral point, not a zone, within the Tas measured. Thermal conductances, ṁwe, and Tb do not vary between Tas of 5-25 C but do increase at 35 C, except for ṁwe in three Perognathus spp. The allometric relationships of mass-specific V̇o2, ṁwe, and thermal conductances to body mass have similar slopes relative to other eutherian mammals; however, the relationships in heteromyids are depressed below those of other eutherians at all temperatures. In general, these physiological variables are depressed in the semixeric-and xeric-dwelling heteromyid species but are similar to those predicted for other eutherians of the same body mass in the three nonxeric heteromyid species. The reduced levels of metabolism and evaporative water loss are considered adaptive for energy and water conservation linked to the familys dietary specialism, granivory.

Energetic cost of feeding territories in an Hawaiian honeycreeper

SummaryBy analysis of time budgets the daily energy expenditure in territorial individuals of a Hawaiian honeycreeper (Vestiaria coccinea, Fam. Drepanididae) were estimated during the nonbreeding season and compared to that of nonterritorial individuals. The mean rise in living costs was 2.3 kcal/24 h or 17% of the nonterritorial energy budget. The most costly territorial behavior was advertisement rather than chasing, and total territorial cost was seen to be little affected by the number of intruders or the size of the territory. These results are compared with data on feeding (nonbreeding) territories of other nectar-feeding birds. The suggestion is made that hummingbirds may be more likely to develop nonbreeding territorial behavior in any set of environmental circumstances than are honeycreepers because of relatively lower total cost of advertisement plus chasing.

Salt and Water Balance in the Terrestrial Phase of the Inland Crab Holthuisana (Austrothelphusa) transversa Martens (Parathelphusoidea: Sundathelphusidae)

Holthuisana is extremely tolerant of dehydration and withstands loss of ca. 45% total body water. During dehydration, water is lost at an equal rate from both hemolymph and tissue compartments. Dehydrated crabs rehydrate by drinking or by absorption of moisture condensing on permeable surfaces, but they cannot absorb water from damp clay soils. In the field, survival is enabled by construction of a vertical burrow (50-70 cm) in heavy clay soil which retains moisture and, therefore, provides high burrow humidity for long periods. The only sources of water available to the crabs during drought are condensation within the burrow and metabolic water.

Water Economy and Energy Metabolism of the Sandy Inland Mouse, Leggadina hermannsburgensis

The effects of ambient temperature on oxygen consumption, evaporative water loss, and body temperature, as well as an overall assessment of water metabolism, were studied in the murid, Leggadina hermannsburgensis , from the arid inland of Australia. Under moderate laboratory conditions, this mouse can subsist indefinitely on a diet of air-dry seed, without drinking water; on such a diet mean urine osmotic concentration was 4711 ± sd 842 milliosmoles per liter. The urine to plasma osmotic pressure ratio was 14.6:1 ± sd 7.5, whereas the ratio for urea was 242:1 ± sd 90. Because Leggadina has a high rate of evaporative water loss, it is concluded that the kidney is the primary means of water conservation. Histological evidence of renal morphology supports this view. Energy metabolism and thermoregulatory ability conform to expected mammalian patterns. A short thermal neutral zone extends from Ta of 31 to 36° C, and the basal metabolic rate is 99.0 per cent of that predicted from body weight. Mean body temperature remained stable between Ta of 10 to 35° C, ranging between 37.5 and 38° C. At an ambient temperature of 37° C, animals became hyperthermic with TB of 39.6° C. Thermal conductance below thermal neutrality was constant, but within and above thermal neutrality it was directly related to ambient temperature.

The Water Requirements of Mourning Doves and Their Use of Sea Water and NaCl Solutions

RELATIVELY little is known of the water requirements of desert R birds, but it appears that many of them lack special mechanisms for water conservation and, unlike some desert rodents, require either water or succulent food (Bartholomew and Cade, 1956). Consequently, the availability of surface water can be an important limiting factor in bird distribution. Since much of the naturally occurring water in deserts is mineralized and since arid regions often include islands and coastal areas where the sea is a possible source of drinking water, a knowledge of the ability of birds to use saline water should contribute to an understanding of their adaptations to desert conditions. To assay the role of saline water in the ecology of birds requires information about their water economy in general. The present study, therefore, undertakes to determine the over-all water requirements of the mourning dove (Zenaidura macroura marginella) as well as its capacity to drink salt water.

Scaling of Evaporative Water Loss in Marsupials

Evaporative water loss was determined at ambient air temperatures of 10-35 C in 10 species of dasyurid marsupials ranging in body mass from 9 to 900 g. Mass-specific evaporative water loss (ṁwe, mg H₂O/g·h) of these marsupials is unrelated to ambient temperatures (Ta) at and below 30 C and is inversely related to body mass (g) by the relationship