Study
Animal Physiology: Adaptation and Environment
Schmidt-Nielsen, Knut
Cambridge University Press, 1997
The standard comparative physiology text, synthesising measurement across animal groups on water and salt balance, temperature regulation, respiration and energetics. The salt-gland and counter-current heat exchange accounts drawn on here rest on the author's own experimental programme from the late 1950s onward.
- Studied in
- Aves, Spheniscidae, Reptilia, Mammalia
- Sample size
- standard reference text on comparative animal physiology
Marine birds excrete excess salt through a nasal gland rather than through the kidney, secreting a fluid substantially saltier than seawater; a bird kidney cannot concentrate urine to that degree. Counter-current arrangements in limbs and extremities allow an animal to keep a warm core while its periphery runs near ambient temperature, and the same anatomy can be bypassed to shed heat.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Physiological problems recur across unrelated lineages, and the same small set of engineering solutions is reached repeatedly because the physics permits few alternatives.
How NatureHQ reads it
Cited as a reference work rather than as a result, which is the honest label for it. It answers a question readers ask of every seabird — how does it drink the sea — with the fact that it does not solve the problem in the kidney at all, because a bird kidney cannot. There is a separate organ above the eyes dumping concentrated brine down the bill, which is why the penguin apparently sneezing on a documentary is not sneezing. The counter-current account is the same shape: not a penguin invention, but a solution that appears wherever a warm animal has thin extremities in cold surroundings.
- A textbook synthesis, so it reports consensus rather than a single measurement with its own error bars.
- Penguins appear as one case among many; species-specific values must be taken from the primary literature.
- Later editions revise detail, and the mechanistic account of salt-gland secretion has advanced since.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Academic book publishersPublished as an academic monograph.
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-11.