Great blue heron (Ardea herodias)
Mallard (Anas platyrhynchos)
Adaptation: a trait, feature, or behavior that helps an organism to survive in a certain environment.
Wading bird: birds adapted to walking through relatively shallow water to look for food and resources, rather than swimming or diving.
Dabbling duck: ducks that graze by tipping forward into the water instead of diving below the surface.
Uropygial gland: a gland located at the base of some birds' tails, which produces oils that the bird can use to coat it's feathers and make them resistant to water.
All living things need food and water to survive. And all animals and plants have unique traits, or adaptations, to support their survival. One of the most incredible examples of animal adaptations are those of wading birds, like the great blue heron.
Wading birds rely on fish and other aquatic organisms for food. You’re most likely to observe them in the Saugus River during low tide. Long, skinny legs keep their bodies and feathers dry while they slowly wade through shallow water searching for food. Thin, spread out toes make it easier for the great blue heron to walk through muddy riverbeds and keep their large bodies balanced. Their sharp eyesight allows them to spot fish beneath the water’s surface. And the great blue heron’s long neck and sharp bill allow it to quickly and forcefully strike its prey. And like all birds species, the heron’s hollow bones make their body much lighter, an adaptation essential for flying.
The double-crested cormorant is another bird species that hunts for food in the water. But unlike the great blue heron, you’re more likely to find the cormorant hunting during high tide.
A whole host of species spring to life and become most active during high tide, when seawater rushes in and deposits a fresh supply of nutrients into the estuary. With deeper water, there’s more space and protection for fish to move around and search for food. And that’s the cue for the cormorant to get hunting.
Cormorants swim in the water and dive for fish beneath the surface. So instead of thin, spread out toes like the heron, the cormorant has webbed feet to help it dive deep and fast underwater. Their webbed feet are an example of a physical adaptation.
You’re also likely to spot the double-crested cormorant standing near the edge of the Saugus River, wings spread out in the sun. Like the heron, the cormorant doesn’t have waterproof feathers. They’ll have trouble flying with heavy wings, soaked in water. So after hunting, cormorants stand with their wings outstretched to heat up and dry in the sun. This is an example of a behavioral adaptation.
But not all birds who swim dry their wings like the cormorant. The mallard is known as a dabbling duck, because they find most of their food at the water’s surface. But they also tip upside down, head underwater, butt in the air, to eat aquatic plants or sift through mud looking for insect larvae. To stay dry, the mallard uses their bill to rub oil on their feathers. And this repels water droplets and keeps their feathers from getting soaking wet while swimming. But where do they get this oil? From a small body organ at the base of their tail, called the uropygial gland, or the preening gland. Most birds have preening glands, but birds like the double-crested cormorant aren't able to secrete enough oil to repel water, like mallards. But because the cormorant’s feathers become saturated with water, they’re able to dive deep and fast, an adaptation they need to hunt for fast moving prey underwater.
As you travel down the Nature Trail, look for physical traits and behaviors that help plants and animals survive. What adaptations can you observe?
All images used in this video are in the public domain.
Video footage of the great blue heron, NPS multimedia.
Video footage of the mallard, courtesy of National Conservation Training Center (NCTC), U.S. Fish and Wildlife Service