When you are at the beach you may have seen some gulls drinking from the ocean and wondered how they could possibly do it. Seagulls can steal your sandwich at the beach and even been known to invade hotel rooms via a balcony just for some food, yet these mischief makers have one key talent that sets them apart from other species: they can drink salt water safely.
The secret is located in their nasal glands, the scientific name for it is their supraorbital glands, which are able to regulate the ionic balance of their blood so well they can drink salt water without dying. Some of the salt is processed as usual by their kidneys, but most of it is simply shot out of their glands. These are positioned in the grooves of their skull, meaning they generally have salt water trickling out of these glands or their nostrils.
They are not alone with this talent, other animals like sea turtles or crocodiles have been known to possess similar glands. That being said even with this mechanism in play saltwater is not their drink of choice, simply because it takes energy to process it. And birds always want to conserve a maximum amount of energy. If freshwater is accessible then they will stick to it.
But when you are flying out many miles to migrate and you just need a drink, then seagulls have no problem surviving off seawater. To put it into perspective if a human was to drink sea water the consequences would be deadly and pretty much immediate. Seawater is around 3% sodium chloride and will cause you to vomit almost immediately, or suffer from extreme nausea with diarrhea. If forced to do so, you could potentially survive off sea water for around 10 days but your body would deteriorate rapidly, it may even speed up dehydrated so it is never recommended.