Each spring and summer, pelicans, herons, egrets, ibises, terns, skimmers and gulls gather on small islands and barrier beaches.
Colonial waterbirds are birds of wetland and marine habitat that build their nests very close together, in colonies. Very often these colonies are on islands. Some birds, like the white ibis, build their nests in trees. Some colonial birds, like flamingo, nest close together on the ground. They usually leave the colony to find food somewhere else. In the case of the white ibis, they need to find food to feed their young that is not as salty (saline) as the food they find for themselves in the colony.
Birds in a breeding colony are in synchrony with each other. They start building their nests at the same time; they lay their eggs at the same time; they raise their young and at the same time; and they roost (sleep) at the same time.
Most colonies can be found in the same place from one year to the next. However, colonies tend to be very sensitive to changes in the environment. If a lagoon becomes polluted, if a predator finds the colony, or if the wetland starts to dry up, the colony will move.
Why would they nest and raise their young in such large groups and so close together? Perhaps that is the only available habitat around. There are many advantages to living in such large groups when raising offspring. With so many birds in the colony, the chances of observing a predator or intruder into the colony are high. Can you imagine how confused that predator will be, when thousands of squawking ibis fly off their nests into the air above? And what about finding a good food source? When there are many individuals looking, chances are some will find what is out there, and the rest will follow them there! Another advantage to living in a large group is that there are many possible future mates to choose from.
Of course there are some disadvantages to living in a colony as well. Think about what it is like to live in a large family. There are so many birds in such a small space!!! Two birds can easily ‘get in each other’s way’ and get into fights — they compete with each other for space, food, and mates. Also, when one bird gets sick, it can easily spread to many birds very quickly.
Threats to Colonial Waterbird Populations
In the past, waterbirds have faced many problems. Around the turn of the century, people collected feathers for the fashion industry. Whole birds were collected for their long filamentous plumes, called "aigrettes," as well as their wings or their entire skins to be worn on hats and other accessories. A breeding colony was a quick and sure source of birds, since tens of thousands of birds could be ‘collected’ at one time. One hunter really understood the birds’ breeding behavior when he noted: "They don't much like to leave their young. I have often shot at these 'strikers' [terns] so fast that I had to put my gun overboard to cool the barrels." Can you imagine, a handful of egret plumes was more than twice the price of an ounce of gold!
Hunting reduced the colonial waterbird populations noticeably along the East coast of the United States. In 1886, George Bird Grinnell organized a group to protest and stop the slaughter. Perhaps you have heard of this group? It is called the "Audubon Society."
Although hunting for feathers is no longer a major threat to continued existence of colonial waterbirds, they face other equally devastating problems today. Wetland habitats for nesting and feeding are disappearing or becoming polluted or disturbed.
Human activity, like off-road vehicles and jet skis, disturb breeding birds. When disturbed adults rise from their nests, leaving their eggs or young exposed to extreme temperatures, it only takes minutes for unattended eggs or young to die from temperature stress or be taken by a predator.
Garbage and litter are real threats to waterbirds. Birds can become entangled in discarded fishing line, struggling until they die. Colonial birds are even more at risk that other types of birds because of their very social lifestyle. Often there are many birds attracted to the garbage. There may be many birds tangled in the same fishing line at the same time. Garbage is attractive to waterbirds. A sparkling coin or a partially-inflated balloon could look like a tasty fish to a bird who is out searching for food to feed its chicks.
These problems can be solved. Preserve and protect the wetland habitat. Make sure you do not litter. Stay away from nesting areas when you are out for a day of fun on the beach.
The next time you see a colony of birds, look closely. What are they doing? Are they nesting? Are they all the same species? Do they interact with each other? What can you do to make sure the habitat will be clean and safe for them to return next year?