The laughing gull (Leucophaeus atricilla) is a medium-sized gull of North and South America. Named for its laugh-like call, it is an opportunistic omnivore and scavenger. It breeds in large colonies mostly along the Atlantic coast of North America, the Caribbean, and northern South America. The two subspecies are: L. a. megalopterus – which can be seen from southeast Canada down to Central America, and L. a. atricilla which appears from the West Indies to the Venezuelan islands. The laughing gull was long placed in the genus Larus until its present placement in Leucophaeus, which follows the American Ornithologists' Union.
Name
The genus name Leucophaeus is from Ancient Greekleukos, "white", and phaios, "dusky". The specific atricilla is from Latinater, "black", and cilla, "tail". Linnaeus appears to have misread his note atricapilla (black-haired), which would have been much more appropriate for this black-headed, but white-tailed, bird.[2]
Range
It breeds on the Atlantic coast of North America, the Caribbean, and northern South America. Northernmost populations migrate farther south in winter, and this species occurs as a rare vagrant to western Europe. The laughing gull's English name is derived from its raucous kee-agh call, which sounds like a high-pitched laugh "ha... ha... ha...".[3]
Laughing gulls breed in coastal marshes and ponds in large colonies. The large nest, made largely from grasses, is constructed on the ground. The three or four greenish eggs are incubated for about three weeks.
Description
This
species is easy to identify. It is 36–41 cm (14–16 in) long with a
98–110 cm (39–43 in) wingspan. The summer adult's body is white apart
from the dark grey back and wings and black head. Its wings are much
darker grey than all other gulls of similar size except the smaller Franklin's gull, and they have black tips without the white crescent shown by Franklin's. The beak is long and red. The black hood is mostly lost in winter.
Laughing gulls take three years to reach adult plumage. Immature
birds are always darker than most similar-sized gulls other than
Franklin's. First-year birds are greyer below and have paler heads than
first-year Franklin's, and second-years can be distinguished by the wing
pattern and structure.
The three-toed sloths are tree-living mammals from Latin America. They are the only members of the genusBradypus and the familyBradypodidae. The four living species of three-toed sloths are the brown-throated sloth, the maned sloth, the pale-throated sloth, and the pygmy three-toed sloth. In complete contrast to past morphological studies, which tended to place Bradypus as the sister group to all other folivorans, molecular studies place them nested within the sloth superfamily Megatherioidea, making them the only surviving members of that radiation.[2][3]
Honduras in the north, through Nicaragua, Costa Rica and Panama into
Venezuela, Colombia, Ecuador, Bolivia, Brazil and eastern Peru
Evolution
A study of mitochondrial cytochrome b and 16S rRNA sequences suggests that B. torquatus diverged from B. variegatus and B. tridactylus about 12 million years ago, while the latter two split 5 to 6 million years ago. The diversification of B. variegatus lineages was estimated to have started 4 to 5 million years ago.[4]
Relation to the two-toed sloth
Both types of sloth
tend to occupy the same forests; in most areas, a particular species of
three-toed sloth and a single species of the somewhat larger and
generally faster-moving two-toed sloth will jointly predominate. Although similar in overall appearance, the two genera are placed in different families. Recent phylogenetic
analyses support the morphological data from the 1970s and 1980s that
the two genera are not closely related and that each adopted their arboreal lifestyles independently.[5] From morphological studies it was unclear from which ground-dwelling sloth
taxa the three-toed sloths evolved or whether they retained their
arboreality from the last common ancestor of sloths. The two-toed sloths
were thought on the basis of morphology to nest phylogenetically within
one of the divisions of ground-dwelling Caribbean sloths.[6]
Our understanding of sloth phylogeny has recently been greatly revised by molecular studies, based on collagen[2] and mitochondrial DNA[3] sequences. These investigations consistently place three-toed sloths within Megatherioidea, close to Megalonyx, megatheriids and nothrotheriids, and two-toed sloths close to mylodontids, while moving the Caribbean sloths to a separate, basal branch of the sloth evolutionary tree.[2][3] These results provide further strong support for the long-held belief that arboreality arose separately in the two genera via convergent paths.
Characteristics
Famously slow-moving, a sloth travels at an average speed of 0.24 km/h (0.15 mph).[7]
Three-toed sloths are about the size of a small dog or a large cat,
with the head and body having a combined length around 45 cm (18 in) and
a weight of 3.5–4.5 kg (8–10 lb). Unlike the two-toed sloths, they also
have short tails of 6–7 cm (2–3 in), and they have three clawed toes on
each limb. They are frequently referred to as three-toed sloths, but
all sloths have three toes; the difference is found in the number of
fingers, meaning that they are now more appropriately referred to as
three-fingered sloths. This idea was first implemented by Judy
Avey-Arroyo, cofounder of the Sloth Sanctuary of Costa Rica, but is now recognized in numerous publications as the correct terminology for these animals.[8]
Behavior
Unlike the two-toed sloth, three-toed sloths are agile swimmers. They are still slow in trees.[9]
The offspring cling to their mother's bellies for around nine months.
They cannot walk on all four limbs, so they must use their front arms
and claws to drag themselves across the rainforest floor.
Three-toed sloths are arboreal (tree-dwelling), with a body
adapted to hang by their limbs. They live high in the canopy, but
descend once a week to defecate on the forest floor. Their long, coarse
fur often appears greenish, not due to pigment, but to algae growing on
it. Sloths' greenish color and their sluggish habits provide an
effective camouflage; hanging quietly, sloths resemble a bundle of
leaves. Large, curved claws help sloths to keep a strong grip on tree
branches.[7]
They move between different trees up to four times a day,
although they prefer to keep to a particular type of tree, which varies
between individuals, perhaps as a means of allowing multiple sloths to
occupy overlapping home ranges without competing with each other.[10]
Three-toed sloths are predominantly diurnal, although they can be active at any hour of the day, while two-toed sloths are nocturnal.[11]
Lifecycle
Members of this genus tend to live around 25 to 30 years, reaching sexual maturation at three to five years of age.
Three-toed sloths do not have a mating season and breed year round. Females give birth to a single young after a gestation period around six months. They are weaned
around nine months of age, when the mother leaves her home territory to
her offspring and moves elsewhere. Adults are solitary, and mark their
territories using anal scent glands and dung middens.[10]
Male three-toed sloths are attracted to females in estrus by their screams echoing throughout the canopy. Sloth copulation lasts an average of 25 minutes.[12]
Male three-toed sloths are strongly polygamous, and exclude competitors
from their territory. Males are also able to compete with one another
within small habitable territories.[13]
The home ranges used by wild brown-throated three-toed sloths in Costa Rica include cacao, pasture, riparian forests, and living fence-rows.
For the first few months after giving birth, mothers remain at just one
or two trees, and guide their young. At about five to seven months of
age, when the young have become more independent, mothers expand their
resources and leave their young in new areas. The home range
for mothers are larger than those of young. After separation, only the
mothers use the cacao agro forest, but both use riparian forest.
Different types of trees are used by both mother and young, which
indicates that this agricultural matrix provides an important habitat
type for these animals.[14]
Dentition and skeleton
Three-toed sloths have no incisor or canine teeth, just a set of peg-shaped cheek teeth that are not clearly divided into premolars and molars, and lack homology
with those teeth in other mammals, thus are referred to as molariforms.
The molariform dentition in three-toed sloths is simple and can be
characterized as dental formula of: 54-5.[15]
Three-toed sloths are unusual amongst the mammals in possessing as many as nine cervical vertebrae, which may be due to mutations in the homeotic genes.[16] All other mammals have seven cervical vertebrae,[17] other than the two-toed sloth and the manatee, which have only six.
Green: B. variegatus, Blue: B. tridactylus, Red: B. torquatus
Mating plumage includes black head and red bill
Definitive alternate plumage
Adult in mid-May (definitive alternate plumage)
Laughing gull, alternate plumage, North Carolina, US, 2016
Adult in winter (definitive basic plumage)
Juvenile
Adult at St. Thomas, Virgin Islands (definitive alternate plumage)
Vagrant in definitive basic plumage in the UK in late 2005
Preparing to land on beach
Los Roques Venezuela
Egg, Collection Museum Wiesbaden
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