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301.
Small endotherms must change roosting and thermoregulatory behaviour in response to changes in ambient conditions if they
are to achieve positive energy balance. In social species, for example many bats, energy expenditure is influenced by environmental
conditions, such as ambient temperature, and also by social thermoregulation. Direct measurements of daily fluctuations in
metabolic rates in response to ambient and behavioural variables in the field have not been technologically feasible until
recently. During different reproductive periods, we investigated the relationships between ambient temperature, group size
and energy expenditure in wild maternity colonies of Bechstein’s bats (Myotis bechsteinii). Bats used behavioural and physiological adjustments to regulate energy expenditure. Whether bats maintained normothermia
or used torpor, the number of bats in the roosts as well changed with reproductive status and ambient temperature. During
pregnancy and lactation, bats remained mostly normothermic and daily group sizes were relatively large, presumably to participate
in the energetic benefits of social thermoregulation. In contrast, smaller groups were formed on days when bats used torpor,
which occurred mostly during the post-lactation period. Thus, we were able to demonstrate on wild animals under natural conditions
the significance of behavioural and physiological flexibility for optimal thermoregulatory behaviour in small endotherms. 相似文献
302.
We describe the earliest fossils of the enigmatic avian taxon Opisthocomiformes (hoatzins) from the Oligo-Miocene (22–24 mya)
of Brazil. The bones, a humerus, scapula and coracoid, closely resemble those of the extant hoatzin, Opisthocomus hoazin. The very similar osteology of the pectoral girdle in the new Brazilian fossil compared to the extant O. hoazin, in which it reflects peculiar feeding adaptations, may indicate that hoatzins had already evolved their highly specialized
feeding behavior by the mid-Cenozoic. We further show that Namibiavis senutae from the early Miocene of Namibia is another, previously misclassified representative of Opisthocomiformes, which documents
that the extant Neotropic distribution of hoatzins is relictual. Because of the weak flight capabilities of hoatzins, their
occurrence on both sides of the South Atlantic is of particular biogeographic interest. We detail that this distribution pattern
is best explained by dispersal from Africa to South America, and that Opisthocomiformes provide the first example of transatlantic
rafting among birds. 相似文献
303.
304.
Solid phase high explosive (HE) residues from munitions detonation may be a persistent source of soil and groundwater contamination at military training ranges. Saturated soil column tests were conducted to observe the dissolution behavior of individual components (RDX, HMX, and TNT) from two HE formulations (Comp B and C4). HE particles dissolved readily, with higher velocities yielding higher dissolution rates, higher mass transfer coefficients, and lower effluent concentrations. Effluent concentrations were below solubility limits for all components at superficial velocities of 10-50 cm day(-1). Under continuous flow at 50 cm day(-1), RDX dissolution rates from Comp B and C4 were 34.6 and 97.6 microg h(-1) cm(-2) (based on initial RDX surface area), respectively, significantly lower than previously reported dissolution rates. Cycling between flow and no-flow conditions had a small effect on the dissolution rates and effluent concentrations; however, TNT dissolution from Comp B was enhanced under intermittent-flow conditions. A model that includes advection, dispersion, and film transfer resistance was developed to estimate the steady-state effluent concentrations. 相似文献