American white pelicans were negatively impacted by DDT.
During the mid-20th
century, DDT (dichlorodiphenyltrichloroethane) was a highly used insecticide that was detrimental to the survival
of populations of fish-eating birds in North America.The chemical was absorbed by aquatic
organisms, and would then bioaccumulate through the food chain.Alarmingly high concentrations were found in
top avian predators, including raptors and, more importantly to this blog post,
pelicans.High concentrations of DDT
resulted in egg-shell thinning, and since pelicans use their webbed feet to
incubate their eggs, they were literally crushing their eggs.Population sizes of brown pelicans and
American white pelicans plummeted.
DDT was sprayed excessively, as shown in this photo.
Fortunately, in 1972, the federal government recognized the impact of
DDT, and the use of the chemical was banned. By the 1980s, pelican populations were
rebounding. Both species of North
American pelicans are now protected under the Migratory Bird Treaty Act of 1918.
This American white pelican chick and its sibling may not have survived had it not been for the ban of DDT.
The American White Pelican may spend most of its time near estuaries and coastal waters, but when it’s time to breed, it moves inland to freshwater lakes and other large water bodies.Pelicans nest colonially, and both males and females perform courtship displays, which includes strutting, bowing, and low flights.The nests are usually built on the ground as a shallow depression in bare soil.Multiple eggs may be laid, but usually only one chick survives due to competition between the siblings.Both parents incubate the eggs and feed the altricial young.After leaving the nest at about 3 weeks of age, the young gather in groups called “crèches” before fledging after 10 weeks.Pelicans have a slow life history - they are able to reproduce at about 3 years of age, and can live up to 20 years.
Breeding adult. Note the tuft of feathers on top of the head and the epidermal plate on the bill.
American White Pelican nesting colony.
The American Bittern is unlike
most other members of Pelecaniformes in that it is not a colonial nester. Male bitterns are polygamous, and vocalize on
their territory as soon as they arrive in early spring. Males also perform a breeding display which
consists of pumping their head and displaying white feathers between their
shoulders. The female chooses the nest
site, usually within reeds or sedges in a wetland, and lays 3-5 eggs. Since males are polygamous, and may often
have multiple females nesting on his territory, females build the nests,
incubate the eggs, and care for the young all on their own. Hatchlings are altricial and usually leave
the nest within two weeks. Due to the
bittern’s secretive natural, information on life history is limited, but it is
believed that age at maturity is about 2 years, and they can live up to 10
years.
In general, members of Pelecaniformes are a bit quieter than other orders of birds, so hearing them in the field can be difficult. However, one may occasionally be able to hear a great blue heron squawking overhead if a nesting colony is nearby. I've always felt that great blues look and sound prehistoric when flying, almost like a pterodactyl. Herons don't really sing so much as they squawk, croak, or honk, which sounds a bit like a scratchy wah-wah-wah-wah. Great examples of all types of great blue calls can be found here.
Great blues are most vocal near their breeding colony.
The members of Pelecaniformes are
considered to be “higher water birds,” as they spend the majority of their time
in or near water and feed on many aquatic organisms, including fish, crabs, and
frogs. These birds also have long,
narrow, or prominent bills, which provide insight into the food they eat. Most members of the order have long legs and
necks.
As recently as a few years ago,
most current members of this order were classified in Ciconiiformes, and
Pelecaniformes consisted of not only pelicans, but cormorants, frigatebirds,
boobies, and anhingas as well. After
molecular analysis was conducted, the latter four groups were moved into a new
order, Suliformes.
Ardeids (bitterns, egrets, and
herons) tend to have either white or grey, brown, or pale blue plumage. Their display feathers were highly desirable during
the late 19th and early 20th centuries, as they were used
to decorate hats. Ardeids are slender
with long, thin necks that aid in catching prey. They generally stand perfectly still,
sometimes for hours, waiting for a fish or frog to swim nearby. The bird then shoots its head and neck
forward to grab or spear the prey. Ardeids fly with their necks retracted in an
S-shape, and they have long, narrow, spider-like toes.
Yellow-crowned night heron. Note the retracted neck while flying.
Great blue heron fishing.
Members of Threskiornithidae have
partly naked faces and partially webbed feet.
They fly with their neck outstretched.
The bills of ibises are very narrow
and curve downward, while the bills of spoonbills are flat and broad. Ibises and spoonbills are morphologically
different and easily differentiated from each other, but they are genetically
similar – hybridization has been documented.
Partially naked faced and curved bill of a white ibis.
Semipalmated feet of a roseate spoonbill.
Pelicans (Pelecanidae) are the
record holders for the longest bill of any bird – up to 50 centimeters long on
the Australian pelican! Their bills are
also unique because of their enormous gular pouches, which are used to scoop up gallons of fish. Similar to Ardeids,
pelicans fly with their necks retracted, but unlike Ardeids, they have webbed
feet. Pelicans have relatively short legs compared to other species in the order, short tails, and long, broad
wings.
American white pelican with black flight feather tips to reduce wear.
Sources
Alderfer, Jonathan. 2006. Complete Birds of North America, pp. 110-124. National Geographic, Washington, D.C.
Peterson, Roger Tory. 2010. Peterson Field Guide to Birds of Eastern and Central North America, 6th Edition, pp. 76-84. Houghton Mifflin Harcourt, Boston and New York.
In eastern North America, there are 3 families,
12 genera, and 21 species of Pelecaniformes. Members of this order are medium to large-sized water birds and wading
birds. They eat fish, frogs, small
birds, crustaceans, and other small critters, and tend to breed colonially. Many species are in decline due to wetland
loss and degradation, pollution, and overharvesting of prey. Members of this order were previously
classified in Ciconiiformes, and prior members of Pelecaniformes can now be
found in Suliformes.
Pelicans (Family Pelecanidae)
are large well-known fish-eaters with very large gular pouches that act as
fishing scoops. They are highly
gregarious but generally silent, save for the occasional grunt and hiss on
breeding colonies. Pelicans were greatly
impacted by DDT in the 1950’s, and residual effects still occur long after the
chemical was banned.
Brown Pelican
Herons, Egrets, and Bitterns (Family Ardeidae) are long-legged and
long-necked water birds that fly with their necks pulled in instead of
outstretched. The bill is generally long
and narrow. Their plumage is varied, and
can be black, white, blue, grey, or brown.
Great Blue Heron
Snowy Egret
Ibises and Spoonbills (Family Threskiornithidae) are also long-legged,
but unlike herons, fly with their neck outstretched. Ibises have narrow bills that curve down,
while spoonbills have large, flat, spoon-like bills
Glossy Ibis
Roseate Spoonbill
Sources:
Alderfer, Jonathan. 2006. Complete
Birds of North America, pp. 110-124. National Geographic, Washington, D.C.
National Audubon Society. 2000. Field
Guide to Birds (Eastern Region), pp. 366-370. Random House, New York.
Peterson, Roger Tory. 2010.
Peterson Field Guide to Birds of Eastern and Central North America, 6th
Edition, pp. 76-84. Houghton Mifflin Harcourt, Boston and New York.
