Why Salt Matters: Maintaining the Supraorbital (Salt) Gland in Seabird Rehabilitation
- Jul 17
- 4 min read
One of the most remarkable adaptations of seabirds is their ability to drink seawater without becoming dehydrated. Whether it's a penguin, albatross, petrel, gull or shag, these birds spend much of their lives at sea where fresh water is often unavailable. Their secret lies in a specialised organ known as the supraorbital gland, more commonly called the salt gland.
Understanding how this gland works—and ensuring it continues to function during rehabilitation—is an important but sometimes overlooked aspect of seabird care.
How do seabirds drink seawater?
Unlike mammals, birds have relatively inefficient kidneys when it comes to removing excess salt. If seabirds relied solely on their kidneys, they would rapidly become overloaded with sodium after eating marine prey or drinking seawater.
Instead, seabirds have evolved paired salt glands located above the eyes within depressions of the frontal bone. These glands contain an extensive network of specialised secretory cells that actively remove excess salts from the bloodstream.
As blood passes through the gland, sodium and chloride ions are transported into tiny ducts, producing an extremely concentrated saline solution. This concentrated brine is then discharged through ducts that open into the nasal passages or near the beak. If you've ever watched a penguin or albatross with salty fluid dripping from its nostrils after returning from sea, you've seen its salt glands at work.
The fluid produced by these glands is remarkably concentrated—often several times saltier than seawater—allowing seabirds to eliminate excess salt while conserving precious body water. Although sodium and chloride make up the majority of the secretion, smaller amounts of potassium, calcium and bicarbonate are also excreted.
Why is this important in rehabilitation?
In rehabilitation, many seabirds are fed thawed fish and have access only to fresh water. While this meets their hydration requirements, it does not adequately stimulate the salt glands.
Research and rehabilitation experience suggest that salt glands begin to lose function surprisingly quickly when they are no longer being used. Functional atrophy may begin within approximately 10 days if birds receive no dietary or environmental salt stimulation.
If the glands become inactive during rehabilitation, birds may struggle to regulate salt balance once released back into the marine environment. Reactivating an atrophied gland takes time and can unnecessarily delay release.
For this reason, maintaining normal salt gland function throughout rehabilitation is far preferable than trying to restore it immediately before release.
Salt supplementation
Several methods have been described for maintaining salt gland function.
Some rehabilitation centres administer salt tablets or coarse uniodised sea salt hidden inside fish. If a bird's salt glands have already become inactive, supplementation should be increased gradually over approximately two weeks before release to allow the glands to regain function.
A commonly described protocol is:
Days 1–3: 25 mg/kg salt
Days 4–6: 50 mg/kg
Days 7–10: 75 mg/kg
Days 11–14: 100 mg/kg
During this period, visible nasal salt secretions indicate that the glands have resumed active salt excretion.
While effective, this approach requires careful dose calculation and close monitoring.
Our approach at Dunedin Wildlife Hospital
At Dunedin Wildlife Hospital we prefer a more natural approach that encourages birds to ingest small amounts of salt water throughout their rehabilitation.
We prepare a 2–3% salt solution (approximately 30 g of coarse sea salt dissolved in 1 litre of water), which closely resembles the salinity encountered in the marine environment.
Using a clean spray bottle, seabirds—including penguins, albatrosses and smaller pelagic species—are lightly misted at least twice daily, usually after feeding.
This simple technique provides several important benefits:
Maintains salt gland function by encouraging ingestion of small amounts of saline during preening.
Promotes natural preening behaviour, helping birds maintain feather condition and waterproofing.
Removes small amounts of food residue from feathers following feeding.
Provides behavioural enrichment, with many seabirds—particularly penguins—appearing to actively enjoy being sprayed.
Because birds regulate their own intake during preening, this method also reduces the risk of accidental over-supplementation that can occur with tablets or concentrated salt boluses.
Can birds receive too much salt?
Although salt supplementation is essential for many marine birds, excessive supplementation can be harmful.
Signs of salt toxicity may include:
Tremors
Lethargy
Reduced appetite
Convulsions
Progressive weakness
If salt toxicity is suspected, supplementation should be discontinued and appropriate veterinary treatment instituted, including fluid therapy and supportive care.
Reports of renal disease associated with salt supplementation have occurred following administration of salt tablets or granules. In many cases, these events were likely multifactorial, with dehydration and inadequate fluid intake contributing alongside excessive salt administration. This highlights the importance of careful dosing, adequate hydration and regular monitoring throughout rehabilitation.
Before release
A seabird's rehabilitation is not complete until it is ready to survive independently in the marine environment.
One useful indicator that the salt glands are functioning appropriately is the presence of visible nasal salt secretions after salt exposure. While this should not be used as the sole criterion for release, it provides reassurance that the glands are actively excreting excess salt and that the bird has retained one of its most important physiological adaptations for life at sea.
Maintaining salt gland function from the beginning of rehabilitation is far easier than trying to restore it later. With simple daily salt supplementation, rehabilitators can help ensure seabirds return to the ocean equipped with the physiological tools they need to thrive.
References
Argilla, L. A. (2025). Feeding Piscivores. Otago Polytechnic.
Hall, E. (n.d.). Rescue & Intensive Care of Seabirds. Australian Wildlife Rehabilitation Conference.
Vidal, C. F. (2018). Seabirds, salt water and the Supraorbital gland. Far South Expeditions.
Written for WReNNZ
by Angelina Martelli - DVN, Cert Avian Wildlife Health
Practice Manager/Senior Wildlife Veterinary Nurse - The Wildlife Hospital, Dunedin