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How do marine birds remove excess salt from their bodies?
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Bird
A brightly colored zebra finch (Taeniopygia guttata) perched on a branch.
Marine birds that consume saltwater utilize specialized nasal glands to maintain their internal osmotic balance. These paired glands, located in indentations of the skull above each eye, are significantly more efficient than the avian kidney at processing high levels of salt.123
The glands extract sodium chloride from the blood and secrete it as a concentrated brine. The method of discharge varies by species:13
- Nostril excretion: In many seabirds, the solution flows through ducts into the nasal cavity and is expelled through the nostrils, where it may drip or be shaken off the bill.13
- Oral discharge: In species such as cormorants and boobies, where the nostrils are closed, the fluid trickles from the internal nares in the roof of the mouth and exits at the tip of the bill.3
These glands are highly adaptive; for instance, individuals of the same species living in marine environments often possess larger salt glands than those in freshwater habitats to accommodate higher salt intake.32