Dolphins with calves produce milk in their mammary glands; dolphins can simultaneously lactate and gestate, so a pregnant dolphin may continue feeding an already-born calf.

Dolphin calves typically stay with their mothers for up to five years, and they may nurse for more than a year during that time.

The average lactation for dolphin calves has not been calculated to date, due to the challenges of studying lactation in non-captive dolphins, although average nursing periods tend to last between 6 months and 2 years.

According to Kristi West and her colleagues at the Sarasota Dolphin Research Program, which collected and analyzed bottlenose dolphin milk samples between 1998 and 2006, calves need high-fat milk.

The proportion of fat available in mother’s milk was directly related to the mass of the calves.

Researchers also found that as fat content decreased and milk water and potassium content rose, calf mass proportionally decreased.

The availability of high-fat prey for the mother is critical to the quality of her milk supply and to the rapid growth and development of her calves.

In their seminal 1940 paper, “The Composition of Dolphin Milk”, Lillian Eichelberger and her colleagues at the University of Chicago found that “it had a fishy odor when freshly drawn and the taste was oily and lacked sweetness.”

(172) Though Eichelberger noted some variation between species, all the samples collected by her team were high in protein and fat, and low in lactose.

Eichelberger classified dolphin milk as “dissimilar to human milk” and found it to more closely resemble the high-calorie milks of rabbits, reindeer, dogs – though the low lactose content sets dolphin milk apart even from these.

(174-175) The researchers noted that, as observed in other mammals, the milk content changes as the calf grows older and lactation nears its end, losing even more lactose content and decreasing in total yield.

Eichelberger speculated that this might be part of an adaptive mechanism to encourage dolphin calves to rely more heavily on other foods (175), while West notes that mothers and calves forage together, the calves eating other foods while continuing to nurse – a gradual weaning process during which calves still rely heavily upon their mothers’ milk.

So how do dolphins nurse and reap the benefits of all that high-fat milk, anyway, since they don’t have lips?

SeaWorld points out the additional challenges of trying to drink a liquid while immersed in a liquid, and explains that dolphins and other marine mammals can roll their tongues into straw-like shapes, complete with zipper-like projections.

These allow dolphin calves’ tongues to form a water-tight seal that keeps milk in and salt water out.

SeaWorld also notes that the thickness of dolphin milk, likened to that of a milkshake, helps dolphin calves drink down as much milk as they can without losing any to their watery surroundings.

Mothers’ milk is especially important for dolphin calves during their youngest days, when the milk provides most or all of their nutrition.

Yet it also sustains calves when they are older and learning to forage and hunt their own prey.