San Francisco State University
Geography 316: Biogeography
The Biogeography of California Brown Pelican (Pelecanus occidentalis californicus)
by Elise Willett, student in Geography 316, Fall 2001
Subspecies: Pelecanus occidentalis californicus
California brown pelicans will use the lift of air and thermals to aid in soaring. They are also very capable of regular flap-gliding over the open sea. Pelicans have emarginated primaries and slotted wing tips (Pennycuick, 1987)
Description of Species:
The brown pelican is the smallest member of seven species of pelicans. There are four subspecies of brown pelicans, two of which reside in the United States, the eastern brown pelican (Pelecanus occidentalis carolinensis) and the California brown pelican (Pelecanus occidentalis californicus). The California brown pelican, as of October 13, 1970 was listed as endangered on both the Federal and State level (Beacham, 2001).
Unmistakable with its
twelve inch long bill and trademark throat pouch the brown pelican is easy to identify.
Measuring about four feet long from bill to tail with a seven feet average wingspan and
weighing approximately eight to eleven pounds, the California brown pelican is one of
Californias largest marine birds (Beacham, 2001).
The early stage of life is easy to determine when looking at a brown pelican
although once mature, exact age is difficult to determine unless they are number banded by
a biologist. Brown pelicans can live twentyfive to thirty years (Cook, 1974) Adult plumage comes in at about three years old, a
little later for male pelicans (Enticott, 1997; Cook, 1974). An adult has a grayish brown
body with a dark belly, a white head and neck merging into a yellowish crown (Thelander,
1994). During courtship their colors become much more vibrant. The chest and head feathers
become golden, the eyes which are normally a yellowish gray (Cruickshank, 1958) turn blue
and the skin surrounding the eye becomes bright
pink (Patent, 1992). Only for the California brown pelican does the throat (gular) pouch
turn bright red with a darker chestnut hind neck (Beacham, 2001), the eastern brown
pelican usually has an iridescent black pouch with red rarely making an appearance
(Cook,1974). When adults are incubating their eggs their eyes and crown begin to fade from
the gold color to a pale yellow. One can tell how close the eggs are to hatching according
to the adults plumage. The more golden the feathers means courtship has just ended
and incubation has just begun and a little yellow means the eggs are about to hatch with
varying degrees in between (Cook, 1974).
|An adult (left) and a
juvenile in Half Moon Bay, CA.
Photo taken by Elise Willett, 2001.
Juvenile brown pelicans are shades of brown and chestnut with white bellies which turn dark with adulthood (Schreiber, Clapp, 1987). It is thought that white bellies contrast less against the sky therefore allowing these young sea birds to get closer to their prey (Craik,1944; Philips, 1962) while learning to perfect the skill of hunting.
Brown pelicans are totipalmate, or "oar
footed", which means all four of their toes are webbed instead of the more commonly
seen three toes webbed with one toe free (Cook, 1974).
All pelicans, have a unique characteristic that makes them look like they are uncomfortable, even when they are resting. there neck looks as though it is twisted and out of place. However, that is the pelican's own special, design for its eighth vertebra is abnormally joined with the seventh and ninth so that it is physically impossible for the pelican to straighten its neck (Sweet, 1975). They have adapted their own interesting and comfortable ways of resting and sleeping positions that lend to their physiology.
Sleeping postures of California brown pelican.
Source: (Schreiber, 1977)
The California brown pelican is a subspecies which can be defined as a geographically limited population whose members possess in common certain taxonomic characters which distinguish them from all other population within the species (Pettingill, 1956).
The brown pelican is the only pelican that is a plunge diver. It scans the ocean for the reflections off of the silvery scales of schooling fish (Thelander, 1994) They rely solely on the ocean as their food source for they are carnivores (USFWS, 2001) and love to eat anchovies (Engraulis mordax). In fact, it is estimated that annually, California brown pelicans off the southern California coast eat about one percent of the total anchovy biomass (Burger, 1988). During their breeding season 90%of the California brown pelicans diet consists of the northern anchovy (Thelander, 1994). Generally, they feed on this northern anchovy, the Pacific sardine and the Pacific mackerel (Thelander, 1994). Breeding success and winter abundance of California brown pelicans have been related to the abundance of food sources. Baldridge (1973) has shown a correlation between the reproductive success of California brown pelicans at Point Lobos with sardine biomass and catches. In 1966, the breeding stopped in this area altogether at the same time that the population of sardines declined. A correlation was also seen in 1979 on Los Coronados Islands in Baja California, Mexico when a decrease in breeding California brown pelicans paralleled a possible over harvest of anchovies in an area with an unrestricted anchovy fishery (Burger, 1988).
The California brown
pelican stays close to shore and hunts for its food usually within five miles of land.
Occasionally, one may travel as far as thirty to forty miles when necessary (Patent,
1992). The brown pelican is a unique feeder
that makes impressive dives from ten to thirty above the surface. They are, however, able
to dive from as high as one hundred feet. The deeper the meal the higher the dive (Cook,
1974). When it sees a potential meal it begins to tip downwards, the wings shape into a V,
and dives. When the bill touches the surface of the water the pelican will push its legs
and wings back creating a bit more force, under the water the bill opens and the pouch
stretches out wide allowing the pelican to scoop up fish. The pelicans hit the water with
such force that even fish six feet below the surface are stunned (Patent, 1992). Air sacs
throughout the birds body help to cushion the shock from the dive. Their pouch,
attached to the lower mandible, when full can hold up to three gallons of water and fish
(Roever, 1974), it is the largest pouch of any bird in the world (Cruickshank, 1958). The
pelican pops up to the surface, tips their head and bill forward letting the water drain
out yet keeping the fish. Then they toss their head back to position the fish head first
and swallow. It is said that brown pelicans can eat as much as four pounds of fish in one
day (Roever, 1974). Another way they feed is by sitting on the surface of the water and
scavenging for food. This has been known to get them in trouble these days due to dying
fish caught in fishing lines that the pelicans too can get caught up in.
pelicans learn to hunt for their food by trial and error. Adult pelicans catch fish on
two-thirds of their dives while immature birds do not fare so well; less than one third of
the immature survive their first year away from their parents (Patent, 1992). Young pelicans can often be found in marinas and
harbors for the easy handouts from fishermen or at fish processing plants where all but
the fillet of a fish is discarded. They soon learn to fish for themselves. Hopefully well
|Here are three juveniles looking for handouts from the fishermen in Half
Moon Bay, CA. Seagulls are a small source of competition for
the brown pelicans. Sometimes the gulls will stand on the pelican's head and steal fish
straight out of their bill (Cruickshank, 1958), but it does not seem to bother the
reserved pelican. Photo taken by: Elise
Nesting, Breeding, and Families:
Pelicans live and nest
in what are called colonies or rookeries. The male picks out a nesting site either on the
ground or in a tree. One of these locations is used to lure a female and if she likes the
site of the nest she may give the male a chance. The female ultimately does the mate
selecting and she must intrude on the nest site (Schreiber, 1977). It is important that
the male is not too aggressive or he will chase away the female, but he needs to be
aggressive enough to avoid another male from moving in on his site (Schreiber, 1977). He
performs a display of head movements and a female will approach usually within two to four
days (Schreiber, 1977) due to either his display, site or plumage or a combination (Cook,
1974). They attempt to mate right away.
The tree nest
consisting of sticks, twigs, and pieces of wood, can sometimes be quite intricate or on
the ground which can be basically no nest at all, however if there is sufficient materials
it is possible that the ground nests may become quite grand and sometimes larger than the
average tree nest (Van Tets, 1965). . The nests are usually close to the other nests,
usually within pecking distance. (Patent, 1992). Only
the male gathers materials for the nest and presents them to the female in a display
movement and she accepts the material with a head sway and then weaves it into the nest.
It takes about seven to ten days until the nest is completed and then the first egg
usually appears within one to three days (Schreiber, 1977). Three chalky white eggs will
be laid, one every other day or so (Thelander, 1994). They are twice as large as a chicken
egg (Cook, 1974) Parents take turns incubating the eggs and use their heavily vascularized
feet to keep the eggs warm. The chicks will hatch in about thirty days, the first laid is
the first to hatch using its egg tooth, and then- the gray skinned, featherless baby
emerges. When the chicks are born they are virtually helpless - they have no sight and are
totally feeble (Roever, 1974). For the next ten days the chicks will grow feathers and the
parents will leave regurgitated fish on the nest floor for the babies to eat, after that
the chicks will eat regurgitation straight from the parents bill, plunging shoulder
deep into their parent's mouth (Short, 1993). The chicks need to eat very well to store
body fat for when they are about eleven weeks, fully fledged and about ready to embark on
their own (Cook, 1974). If food sources are low only one chick will get fed and therefore
survive, if supply is good two or possibly all three will survive, The average fledging
rate is about 1.5 per successful nest, coupled with a chick and first year mortality rate
of 60-70% (Thelander, 1994). Sometimes the older chick(s) may attack the smaller chick(s)
preventing feedings or just beating it to death (Patent, 1992). While they are babies the
parents need to protect them at all times from predators such as gulls, feral cats,
skunks, from the harsh rays of the sun, and from the cold (Cook, 1974). As an adult the
California brown pelican has very few predators (Bakker, 1984).
While they are babies the parents need to protect them at all times from predators such as gulls, feral cats, skunks, from the harsh rays of the sun, and from the cold (Cook, 1974). As an adult the California brown pelican has very few predators (Bakker, 1984).
Nestling California brown pelicans tend to first make a choking bark sound and later a loud raspy scream that goes k-r-r-r-ing. Flying young make a "dignified groaning" sound. Adults are virtually mute (Cruickshank, 1958) except in the event of threat or courtship when they make a groaning or popping sound which results from their jaws snapping (Cook, 1974).
It is believed
that birds have evolved from a specimen that paleontologists refer to as Archeopteryx
(ancient winged creature) that was about the size of a crow (Beebe, 1965). It was similar
to a lizard in that its tail was long and jointed, but all of its twenty joints were lined
with feathers. This was the discovery that had finally linked birds and reptiles together
and proving beyond a doubt that these two had a common ancestor (Beebe, 1965). The
Archeopteryx had formed plumage on its wings and tail which tells us that feathers were
already close to perfection by about six million years ago (Beebe, 1965). Its wings,
however, were weak suggesting that it was not a true flyer but more along the lines of a
flutterer, maybe even just jumping from one tree to the next. This is just
common ancestry that we are talking about, according to C. William Beebe (1965) the key to
evolution is adaptive radiation:
out or radiating of bird-forms descended from an ancient stem, into all areas of the
earth, each form coming into contact with a particular environment to adjust itself to
which, its various organs and parts exercise different functions, until the friction
of the struggle for existence has molded each to its particular niche. If its
lines lie in happy places, its race is established
and Evolution marks another
success in its inexorable movement onward and upward, - a new species is born!
|Cladogram showing possible taxonomic origin of the Pelecanidae family.|
|Source: Van Tets, 1965|
A lot of people commonly mistake the pterodactyl as a relative of the bird but not so, because they never developed feathers, the important ingredient to becoming a bird. The pterodactyl depended on a webbed skin to fly such as that of a bat.The all-important feather has evolved from skin structures, which at an early stage of growth resemble the cells of fish and reptile scales.
Only a fraction of species of birds exist today out of the original 1,634,000 that once existed. During the Paleocene and Eocene periods (37 to 65 million years ago) when birds first took to the air, some scientists say the pelicans were there making that flight (Scott, 1975). It is believed that the pelicans fossil record has barely changed in 30 to 40 million years and that many species of pelicans have already become extinct (Roever, 1974). >
Pelicans have a few characteristics that they have evolved that set them apart from all other birds. First, their tongue, which one would envision as huge given the size of the bird and its bill, is a small inconspicuous flap no larger round than a toothpick (Beebe, 1965). The reason for this adaptation is due to the fact that all pelicans swallow their food whole and a tongue of any substantial size would impede that process (Beebe, 1965). Another characteristic they have developed is its beak which doesnt just capture prey, but performs many functions. It preens and oils its feathers distributing oil from glands at the base of the tail which helps waterproof the bird. When the bill cannot reach a spot the pelican has a backup plan, it uses its middle nail which is serrated internally to get to those hard to reach places (Nutthall, 1974). In conjunction with the bill, the pouch, a distinguishing feature of a pelican, is a fish net, an aide in mate attraction, and a cooling device. When the pelican gets too hot, it opens its bill and flutters the sides of its pouch. The movement of the pouch skin keeps air flowing over the moist surface where water evaporates from the surface. It is the same concept as when humans sweat (Patent, 1992). They also possess the unique adaptation of the ability to drink seawater.
An offshore island like this
one off of San Francisco's Ocean Beach is a typical roosting habitat for California brown
pelicans. You can see here, two pelicans taking flight to search the open water for
(Photo taken by: Elise Willett, 2001 )
California brown pelicans are
aquatic birds and are typically found on rocky,
sandy or vegetated offshore islands, beaches
(U.S.F.W.S., 2001), open sea (for feeding),
harbors, marinas, estuaries, and
breakwaters (Small, 1994)
Map of Distribution:
|One can see that the historic breeding range once extended halfway up the state. Currently, in California, they only breed on and near the Anacapa and Santa Barbara Islands.; Source: Thelander, Carl. 1994|
California brown pelicans can be found along the entire length of California, primarily along the coast and on offshore islands, the largest numbers being seen in the summer and most remaining until November (Garrett & Dunn, 1981; Small, 1994).
Their breeding range, historically, was from coastal central Mexico up to Point Lobos in Monterey until about the 1950's (Thelander, 1994).Currently, their known nesting colonies are on the Anacapa Island, Santa Barbara Island and nearby Sutil Rock, Scorpion Rock near Santa Cruz Island which are all a part of the Channel Islands located off southern California's coast. In the 1980s the Channel Islands hosted 6,000 breeding pairs (Thelander, 1994). Colonies are found on Los Coronados Islands, which are near the United States and Mexico border. (Garrett & Dunn, 1981 Beacham, 2001). The majority of the nesting pairs are found down south on islands off the Pacific coast of Baja, Mexico, and in the Gulf of California (Thelander, 1994). Their nest habitat is almost always on a coastal island around six feet above high tide level (Beacham, 2001).
After nesting season is over the California brown pelican will usually follow the food supply north up the coast to Canada and British Colombia, its historical dispersal range. This dispersal is responsible for the influx of the Mexican breeding population to the California coast in the months of May through October (Thelander, 1994).
Pelecanus occidentalis californicus are found all along the state with some particular sites being the Channel Islands, the Farallon Islands in San Francisco County, Ano Nuevo Island in San Mateo County, and the San Pedro Harbor in L.A. County (Thelander, 1994). Also Point Reyes and Point Bonita in Marin County, Pacific Grove, Carmel and Point Loma in Monterey County, Point Fermin and Dana Point in L.A. The Salton Sea in Imperial County is an important post breeding site for pelicans from the Gulf of California.
Threats to the California Brown Pelican:
Pesticide pollution poses a double threat to the survival of the brown pelicans: direct poisoning and impaired reproduction (Beacham, 2001). The culprit was DDT, a chemical that was used in agriculture until 1972 when it was banned by the Environmental Protection Agency. In the 1960's the threat of pesticide pollution to brown pelicans became obvious to biologists, they discovered that the eggshells were thinning causing a devastating effect to the nesting population off southern California. DDT was able to contaminate the sea after being applied to agricultural areas, rain washes the chemical from the plants and soil into streams tat end up in the Pacific. Much of the DDT was applied aerially by crop dusters and never even reaching the land, but was carried by wind currents and precipitated into the sea many miles from the original source (Small, 1974) In addition, an L.A. County DDT manufacturing plant was dumping their waste into the sewer system which would end up in the coastal waters and into the food chain (Thelander, 1994). DDT is an aggressive and long lived compound that does not break down easily or quickly. It is fat soluble and accumulates to its higher concentration (Small, 1994). The chemical enters the bodies of tiny marine diatoms and deposits in the microscopic drops of oil which all living organisms have in their cells. Next, zooplankton (tiny marine animals) come along and eat the diatoms all the while the DDT remains unchanged and accumulates to a higher concentration with each feeding level (Small, 1994). By the time it reaches the bodies of the anchovies that brown pelicans like to eat the concentration of DDT has reached ten to twenty parts per million in each fish giving the pelican a hefty dose of concentrated poison (Small, 1994). The concentration within a female California brown pelican's body can reach as high as 100 parts per million meaning that the DDT has multiplied approximately 1,000,000 times from its initial state when it was sprayed on crops far from the ocean (Small, 1974).
DDT interferes with the hormone cycle and production involved in the mobilization of calcium from female bones in order to produce a strong eggshell of a particular necessary thickness. The breaking point for an eggshell is when it is 20% thinner than normal (Small, 1974), and when an expecting parent hops on their nest to incubate their eggs they will crush the eggs under their weight. In 1969, it was recognized in the California brown pelican that there was a definite problem, nestling production had virtually ceased. However, surveys showed that the colonies in the Gulf of California were DDT free, so there was still hope for a recovery. Since the ban of DDT, the California brown pelican has done a nice job of recovering, although it still listed as endangered and continues to be protected by the Endangered Species Act. The eastern brown pelican (Pelecanus occidentalis carolinensis) has since been removed from the federal list of endangered species (Beacham, 2001).
Another recent threat is avian botulism. a 1996 outbreak killed at least 1,125 California brown pelicans, 8,525 American white pelicans (Pelecanus erythrorhynchos), and 4,400 other seabirds in the Salton Sea (Beacham, 2001). This is possibly linked to large kills of tilapia, an introduced African fish. Avian botulism is a disease that attacks water birds and is caused by a toxin produced by anaerobic bacteria (Beacham, 2001). The bacterial disease first attacks the fish making them sick, toxic and an easy meal for the birds (Beacham, 2001). The birds ingest the fish and the potential fatal amount of toxins. A direct link has not yet been proven by biologists, however, this could be a real threat to the recovery and preservation of an already fragile population of California brown pelicans.
Most of the time the pelicans are adored and loved by humans. The only exception would be some fishermen who believe the brown pelicans to be a source of competition for the anchovies which are used to make fish meal for chicken and other livestock feed (Patent, 1992).
Careless fishermen can pose a worse threat to the brown pelicans by leaving fishing line and fish hooks in feeding and roosting areas. The pelicans are attracted to struggling fish that are caught on a line, and think it a tasty, easy meal. Many brown pelicans get caught in the line and either get strangled or starve to death. Often times the hooks will puncture their pouch leaving large holes that are not conducive to successful hunting. The best thing for a tangled pelican is for it to be freed from the line itself, not just freed, for the bird will still be impaired with the line still around its body. The pelicans are easily freed due to their docile and harmless demeanor.
Human can also hurt the brown pelican population directly by disturbing the nesting areas. Tourists, researchers, and photographers, if they get too close too often will chase the parents away leaving the chicks all alone and vulnerable.
healthy adult California brown pelican. Notice his "oar-footed" or
totipalmate foot. Also at the end of his beak what looks like a drop of water
is really his egg tooth and preening aide.
Photo Taken by Elise Willett, 2001.
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