Yellow-shouldered Blackbird
Encyclopedia
The Yellow-shouldered Blackbird (Agelaius xanthomus), also known as La Mariquita de Puerto Rico or Capitán, is a diurnal
blackbird
endemic
to the archipelago
of Puerto Rico
and one of the eleven species belonging to the Agelaius genus of the Icteridae family.
in 1862 by Philip Sclater
as Icterus xanthomus. The species is closely related to, and possibly derived from, the Red-winged Blackbird
(Agelaius pheoniceus). The Tawny-shouldered Blackbird
(Agelaius humeralis), a species from Cuba
and Haiti
, is morphologically intermediate between A. xanthomus and A. humeralis. Until recently, some authors considered A. xanthomus as a subspecies of A. humeralis. The 1983 American Ornithologists' Union
edition considered A. xanthomus, together with A. humeralis, a superspecies
. The main physical difference between A. xanthomus and A. humeralis resides in their bills
, with A. humeralis being broader toward the base. The recognized subspecies A. x. monensis, or Mona Yellow-shouldered Blackbird, was described by Barnes in 1945 from the islands of Mona
and Monito
.
coloration is indistinguishable between the sexes, sexual dimorphism
is present in this species with males being larger than females. Plumage abnormality is rare in this species. Adult individuals measure from 20–23 cm (7.9–9.1 in); on average, males weigh 41 g (1.4 oz) and females weigh 35 g (1.2 oz). Sexual categorization may also be made by measurement of the wings, with males' being 1.1 times larger and having a mean
length of 102 cm (40.2 in), while females' wings have an average length of 93.3 cm (36.7 in).
The species was once commonly found in the coastal forests of the archipelago of Puerto Rico but during the early 20th century these forests were destroyed to allow for the development of sugarcane
plantations. After the decline of the sugar industry after the 1930s the coastal areas were developed for housing. As a result, the species is now limited to three areas: the islands of Mona and Monito
, where a subspecies developed (A. g. xmonensis); the Roosevelt Roads Naval Station
area in eastern Puerto Rico; and the southern Puerto Rican dry forests
and mangrove
s. Although all three locations are considered coastal subtropical dry forests, the species has been observed as far inland as the mountain town of Lares
and in subtropical wet forests
during the non-breeding season. The species has also been observed at the Cabo Rojo National Wildlife Refuge
. The destruction of habitat and brood parasitism
by the Shiny Cowbird
(Molothrus bonariensis) led to a drastic population decline during the mid-70s to early 80s. In 1976, the population of the nominate form was estimated at 2000 individuals but in 1982 the population estimate dropped to 300 individuals. Conservation efforts have increased the population to 1250 pairs.
In 1976 Post and Wiley estimated the Mona subspecies population at 200 individuals. Subsequent roost counts and studies from 1981 to 1995 estimated the population at anywhere between 220 to 400 individuals. Studies performed in the island of Monito, located 5 km (3.1 mi) northwest of Mona, revealed an average of 25 individuals with breeding also being observed. The studies also revealed that birds traveled from the west coast of Mona to Monito.
Yellow-shouldered Blackbirds are non-migratory birds, but a portion of the population of the nominate form moves from coastal areas to inland areas during the non-breeding season to feed.
, but are considered to be arboreal insectivore
s since the majority of their diet consists of insect
s. Wetmore
and Post performed studies to determine the dietary habits of the nominate form A. x. xanthomus. The studies analyzed the stomach contents of several individuals (25 by Post and 55 by Wetmore) and found evidence of consumption of insects belonging to the orders
Lepidoptera
, Orthoptera
, Homoptera
, Coleoptera, Diptera
, Dermaptera and Hymenoptera
, arachnid
material of the order Araneae, unidentified molluscs, and plant matter. Aside from natural material, the species also consumes processed food such as cattle ration, human food (cooked rice and sugar), dog food and monkey chow. Plant matter was acquired from processed foods while insects are gleaned
from the canopy
and sub-canopy layers of trees. During the nesting season their diet is composed of 90% arthropod material.
Studies have not been performed to determine the dietary habits of the Mona subspecies, but consumption of insects, spiders, fruits from Pithecellobium
spp. and the cacti Selenicereus spp., Pilosocereus royenii, Harrisia portoricensis
, and Opuntia
spp., seeds from gumbo limbo (Bursera simaruba
) and Ficus
spp. and nectar from Aloe vera
, yucca
and Croton discolor have been observed.
commonly spans from April to August but breeding activity has been observed from February to November. The breeding season's start coincides with the start of the rainy season, thus explaining the fluctuation in the start and end of the breeding season. The species is believed to be monogamous
with a single attempt at nesting per year and with nesting being performed in loose colonies. Nests of both the nominate form and the Mona subspecies contain from 1 to 4 eggs
with an average of 3 eggs. Eggs are blue-green with brown spots and are incubated
for 13 days by the female. Both sexes reach sexual maturity
at 1 year of age. As with other Agelaius species, it usually builds open, cup-shaped nests in trees, but nest locations and shapes may vary depending on location and availability of building materials. The Roosevelt Roads's population builds nests on hollows in dead mangroves, while the Mona subspecies builds nests in ledges or crevices near the coastal cliffs. In all, the species uses eight distinct nesting habitats: mudflat
s and salinas
; offshore red mangrove
cays; black mangrove
forest; lowland pastures (dry coastal forest); suburban areas; coconut
plantations; and coastal cliffs. Building of the nest is performed solely by females while feeding of the young is performed by both sexes. Nestlings leave the nest 13 to 16 days after hatching. Males defend small territories, usually around 3 metres, during the nesting period. Before the nesting period males defend slightly larger territories to repel other males.
Yellow-shouldered Blackbirds engage in anting
, a rare behavior only observed in the Puerto Rican Tanager
among West Indian birds. Individuals were observed applying Pheidole
spp. ants to its body and feathers for a short period of time (8 min.).
The species engages in mobbing, a behavior in which a pack of birds, from one or more species, attack a known predator (usually to defend eggs or hatchling
s).
The Yellow-shouldered Blackbird was listed as an endangered species on November 19, 1976 by the U.S. Fish and Wildlife Service. Critical habitat was subsequently established for the entire Mona and Monito islands, the Roosevelt Roads Naval Station in Ceiba
, an area expanding from Cabo Rojo
to Guánica
in the southwest region of Puerto Rico, and a small area in San Germán
.
Diseases such as avian pox
have been associated with extinction of bird populations such as Hawaiian honeycreeper
s. For this species only one type of parasite has been observed, the chewing louse
(formerly classified as Mallophaga), with three species being observed: Philopterus agelaii; Machaerilaemus spp.; and Myrsidea spp. The parasites predominantly occur in the head area with adult males having the highest infestation percentage and juveniles having a lower infestation rate than adults. The mite
s Ornithonyssus bursa and Anclrolaelaps casalis have also been observed in nests, but the information presently available does not indicate they are a threat. Another disease commonly experienced by Yellow-shouldered Blackbirds is fowlpox
, also known as avian pox. Lesions caused by this disease occur in exposed areas such as the legs and the bend of the wings.
Nest predation has been an important contributor to the decline of the Yellow-shouldered Blackbird. Known terrestrial predators include rat
s (Rattus rattus), mongoose
s and feral cats, all introduced species
to Puerto Rico. Rats constituted the main nest predator eating both eggs and hacthlings. A 1983 report concluded that rat predation accounted for 48% of nest failures that year. The majority of the activity coincided with the recession of water from July to August which exposed the mangrove nesting area to dry land. Since the middle 1980s artificial PVC nesting structures have been created in mudflats surrounding mangrove forests to reduce rat predation. These structures replaced old wooden nesting boxes and were readily accepted by the species. Presently, few (1 to 2) natural nests are observed each year in the area.
The loss of feeding and breeding habitat and brood parasitism by the Shiny Cowbird
are among other threats that limit and endanger the Yellow-shouldered Blackbird populations. Natural predators, such as the Pearly-eyed Thrasher
(Margarops fuscatus), also represent a threat, although minor, to the populations. These animals have been reported to steal eggs and young from nests and to also destroy or steal nesting materials which in many cases leaves the young as prey for the predators.
Diurnal animal
Diurnality is a plant or animal behavior characterized by activity during the day and sleeping at night.-In animals:Animals that are not diurnal might be nocturnal or crepuscular . Many animal species are diurnal, including many mammals, insects, reptiles and birds...
blackbird
Icterid
The Icterids are a group of small to medium-sized, often colorful passerine birds restricted to the New World. Most species have black as a predominant plumage color, often enlivened by yellow, orange or red. The family is extremely varied in size, shape, behavior and coloration...
endemic
Endemism in birds
An endemic bird area is a region of the world that contains two or more restricted-range species, while a "secondary area" contains one or more restricted-range species. Both terms were devised by Birdlife International....
to the archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
of Puerto Rico
Puerto Rico
Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...
and one of the eleven species belonging to the Agelaius genus of the Icteridae family.
Taxonomy
The nominate form of the Yellow-shouldered Blackbird (A. x. xanthomus) was first described from Puerto Rico and ViequesVieques, Puerto Rico
Vieques , in full Isla de Vieques, is an island–municipality of Puerto Rico in the northeastern Caribbean, part of an island grouping sometimes known as the Spanish Virgin Islands...
in 1862 by Philip Sclater
Philip Sclater
Philip Lutley Sclater was an English lawyer and zoologist. In zoology, he was an expert ornithologist, and identified the main zoogeographic regions of the world...
as Icterus xanthomus. The species is closely related to, and possibly derived from, the Red-winged Blackbird
Red-winged Blackbird
The Red-winged Blackbird is a passerine bird of the family Icteridae found in most of North and much of Central America. It breeds from Alaska and Newfoundland south to Florida, the Gulf of Mexico, Mexico, and Guatemala, with isolated populations in western El Salvador, northwestern Honduras, and...
(Agelaius pheoniceus). The Tawny-shouldered Blackbird
Tawny-shouldered Blackbird
The Tawny-shouldered Blackbird is a species of bird in the Icteridae family.It is found in Cuba, the Dominican Republic, Haiti, and the United States....
(Agelaius humeralis), a species from Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...
and Haiti
Haiti
Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...
, is morphologically intermediate between A. xanthomus and A. humeralis. Until recently, some authors considered A. xanthomus as a subspecies of A. humeralis. The 1983 American Ornithologists' Union
American Ornithologists' Union
The American Ornithologists' Union is an ornithological organization in the USA. Unlike the National Audubon Society, its members are primarily professional ornithologists rather than amateur birders...
edition considered A. xanthomus, together with A. humeralis, a superspecies
Superspecies
A superspecies is a group of at least two more or less distinctive species with approximately parapatric distributions. Not all species complexes, whether cryptices or ring species are superspecies, and vice versa, but many are...
. The main physical difference between A. xanthomus and A. humeralis resides in their bills
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
, with A. humeralis being broader toward the base. The recognized subspecies A. x. monensis, or Mona Yellow-shouldered Blackbird, was described by Barnes in 1945 from the islands of Mona
Mona, Puerto Rico
Mona is the third largest island of the archipelago of Puerto Rico, after the main island of Puerto Rico and Vieques. It is the largest of three islands located in the Mona Passage, a strait between the Dominican Republic and Puerto Rico, the others being Monito Island and Desecheo Island...
and Monito
Monito Island
Monito Island is an uninhabited island about 5 kilometers northwest of much larger Mona Island. Monito is the masculine diminutive form of Mona in Spanish. It is one of three islands in the Mona Passage, and part of the Isla de Mona e Islote Monito barrio, a subdivision of the municipality of...
.
Physical description
The Yellow-shouldered Blackbird, as its name implies, is a glossy black bird with a small yellow humeral patch around its "shoulders" outlined by a white margin. Immature individuals possess a duller coloration and a brown abdomen. Although plumageFeather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
coloration is indistinguishable between the sexes, sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
is present in this species with males being larger than females. Plumage abnormality is rare in this species. Adult individuals measure from 20–23 cm (7.9–9.1 in); on average, males weigh 41 g (1.4 oz) and females weigh 35 g (1.2 oz). Sexual categorization may also be made by measurement of the wings, with males' being 1.1 times larger and having a mean
Arithmetic mean
In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...
length of 102 cm (40.2 in), while females' wings have an average length of 93.3 cm (36.7 in).
Habitat and distribution
Sugarcane
Sugarcane refers to any of six to 37 species of tall perennial grasses of the genus Saccharum . Native to the warm temperate to tropical regions of South Asia, they have stout, jointed, fibrous stalks that are rich in sugar, and measure two to six metres tall...
plantations. After the decline of the sugar industry after the 1930s the coastal areas were developed for housing. As a result, the species is now limited to three areas: the islands of Mona and Monito
Monito Island
Monito Island is an uninhabited island about 5 kilometers northwest of much larger Mona Island. Monito is the masculine diminutive form of Mona in Spanish. It is one of three islands in the Mona Passage, and part of the Isla de Mona e Islote Monito barrio, a subdivision of the municipality of...
, where a subspecies developed (A. g. xmonensis); the Roosevelt Roads Naval Station
Roosevelt Roads Naval Station
Roosevelt Roads Naval Station is a former United States military air base in the town of Ceiba, Puerto Rico. The site is run today as José Aponte de la Torre Airport, a public use airport.-History:...
area in eastern Puerto Rico; and the southern Puerto Rican dry forests
Puerto Rican dry forests
The Puerto Rican dry forests are a subtropical dry forest ecoregion located in southwestern and eastern Puerto Rico and on the offshore islands. They cover an area of . These forests grow in areas receiving less than of rain annually...
and mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s. Although all three locations are considered coastal subtropical dry forests, the species has been observed as far inland as the mountain town of Lares
Lares, Puerto Rico
Lares is a small mountain municipality of Puerto Rico's central-western area located north of Maricao and Yauco; south of Camuy, east of San Sebastián and Las Marias; and west of Hatillo, Utuado and Adjuntas. Lares is spread over 10 wards and Lares Pueblo...
and in subtropical wet forests
Puerto Rican moist forests
The Puerto Rican moist forests are a tropical moist broadleaf forest ecoregion on the archipelago of Puerto Rico. They cover an area of .-Lowland forests:Lowland forests are found throughout the island's coastal lowlands except for the dry southwest...
during the non-breeding season. The species has also been observed at the Cabo Rojo National Wildlife Refuge
Cabo Rojo National Wildlife Refuge
Cabo Rojo National Wildlife Refuge is located on the southwestern side of Puerto Rico in the municipio of Cabo Rojo. It was established in 1974, when 587 acres of land were obtained by the U.S. Fish and Wildlife Service from the Central Intelligence Agency which had operated the Caribbean Bureau of...
. The destruction of habitat and brood parasitism
Brood parasite
Brood parasites are organisms that use the strategy of brood parasitism, a kind of kleptoparasitism found among birds, fish or insects, involving the manipulation and use of host individuals either of the same or different species to raise the young of the brood-parasite...
by the Shiny Cowbird
Shiny Cowbird
The Shiny Cowbird, Molothrus bonariensis, is a passerine bird in the New World family Icteridae. It breeds in most of South America apart from the most dense jungles, mountains and deserts , the coldest southernmost regions , and on Trinidad and Tobago...
(Molothrus bonariensis) led to a drastic population decline during the mid-70s to early 80s. In 1976, the population of the nominate form was estimated at 2000 individuals but in 1982 the population estimate dropped to 300 individuals. Conservation efforts have increased the population to 1250 pairs.
In 1976 Post and Wiley estimated the Mona subspecies population at 200 individuals. Subsequent roost counts and studies from 1981 to 1995 estimated the population at anywhere between 220 to 400 individuals. Studies performed in the island of Monito, located 5 km (3.1 mi) northwest of Mona, revealed an average of 25 individuals with breeding also being observed. The studies also revealed that birds traveled from the west coast of Mona to Monito.
Yellow-shouldered Blackbirds are non-migratory birds, but a portion of the population of the nominate form moves from coastal areas to inland areas during the non-breeding season to feed.
Diet
Yellow-shouldered Blackbirds are omnivorousOmnivore
Omnivores are species that eat both plants and animals as their primary food source...
, but are considered to be arboreal insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
s since the majority of their diet consists of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s. Wetmore
Alexander Wetmore
Frank Alexander Wetmore was an American ornithologist and avian paleontologist.-Life:Wetmore studied at the University of Kansas...
and Post performed studies to determine the dietary habits of the nominate form A. x. xanthomus. The studies analyzed the stomach contents of several individuals (25 by Post and 55 by Wetmore) and found evidence of consumption of insects belonging to the orders
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
, Orthoptera
Orthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
, Homoptera
Homoptera
Homoptera is a deprecated suborder of order Hemiptera; recent morphological studies and DNA analysis strongly suggests that the order is paraphyletic. It was therefore split into the suborders Sternorrhyncha, Auchenorrhyncha, and Coleorrhyncha....
, Coleoptera, Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, Dermaptera and Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
material of the order Araneae, unidentified molluscs, and plant matter. Aside from natural material, the species also consumes processed food such as cattle ration, human food (cooked rice and sugar), dog food and monkey chow. Plant matter was acquired from processed foods while insects are gleaned
Gleaning (birds)
Gleaning is a term for a feeding strategy by birds in which they catch invertebrate prey, mainly arthropods, by plucking them from foliage or the ground, from crevices such as rock faces and under the eaves of houses, or even, as in the case of ticks and lice, from living animals. This behavior is...
from the canopy
Canopy (forest)
In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...
and sub-canopy layers of trees. During the nesting season their diet is composed of 90% arthropod material.
Studies have not been performed to determine the dietary habits of the Mona subspecies, but consumption of insects, spiders, fruits from Pithecellobium
Pithecellobium
Pithecellobium is a genus of flowering plants in the pea family, Fabaceae. The generic name is derived from the Greek words πιθηκος , meaning "ape" or "monkey," and ελλοβιον , meaning "earring," which refers to the coiled shape of the seedpods.Delimitation to the closely related Albizia is a matter...
spp. and the cacti Selenicereus spp., Pilosocereus royenii, Harrisia portoricensis
Harrisia portoricensis
Harrisia portoricensis is a species of cactus in the genus Harrisia. Its common name is higo chumbo. It is endemic to Puerto Rico, where it is known from three smaller islands off the coast of the main island. The population is estimated at 59,000 on Mona Island, 148 individuals on Monito Island,...
, and Opuntia
Opuntia
Opuntia, also known as nopales or paddle cactus , is a genus in the cactus family, Cactaceae.Currently, only prickly pears are included in this genus of about 200 species distributed throughout most of the Americas. Chollas are now separated into the genus Cylindropuntia, which some still consider...
spp., seeds from gumbo limbo (Bursera simaruba
Bursera simaruba
Bursera simaruba, commonly known as the Gumbo-limbo, is a tree species in the family Burseraceae, native to tropical regions of the Americas from the southeasternmost United States south through Mexico and the Caribbean to Brazil and Venezuela...
) and Ficus
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
spp. and nectar from Aloe vera
Aloe vera
Aloe vera, pronounced , also known as the true aloe or medicinal aloe, is a species of succulent plant in the genus Aloe that is believed to have originated in the Sudan. Aloe vera grows in arid climates and is widely distributed in Africa, India, Nepal and other arid areas.The species is...
, yucca
Yucca
Yucca is a genus of perennial shrubs and trees in the family Asparagaceae, subfamily Agavoideae. Its 40-50 species are notable for their rosettes of evergreen, tough, sword-shaped leaves and large terminal panicles of white or whitish flowers. They are native to the hot and dry parts of North...
and Croton discolor have been observed.
Reproduction and behavior
The Yellow-shouldered Blackbird breeding seasonBiological reproduction
Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction...
commonly spans from April to August but breeding activity has been observed from February to November. The breeding season's start coincides with the start of the rainy season, thus explaining the fluctuation in the start and end of the breeding season. The species is believed to be monogamous
Monogamy
Monogamy /Gr. μονός+γάμος - one+marriage/ a form of marriage in which an individual has only one spouse at any one time. In current usage monogamy often refers to having one sexual partner irrespective of marriage or reproduction...
with a single attempt at nesting per year and with nesting being performed in loose colonies. Nests of both the nominate form and the Mona subspecies contain from 1 to 4 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
with an average of 3 eggs. Eggs are blue-green with brown spots and are incubated
Avian incubation
Incubation refers to the process by which certain oviparous animals hatch their eggs, and to the development of the embryo within the egg. The most vital factor of incubation is the constant temperature required for its development over a specific period. Especially in domestic fowl, the act of...
for 13 days by the female. Both sexes reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 1 year of age. As with other Agelaius species, it usually builds open, cup-shaped nests in trees, but nest locations and shapes may vary depending on location and availability of building materials. The Roosevelt Roads's population builds nests on hollows in dead mangroves, while the Mona subspecies builds nests in ledges or crevices near the coastal cliffs. In all, the species uses eight distinct nesting habitats: mudflat
Mudflat
Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of...
s and salinas
Salinas
-People:*Anita Reeves Salinas, Chilean television, film and theatre actress*Camilo Salinas, Chilean musician*Carlos Salinas de Gortari, a Mexican president*Francisco de Salinas, a 16th century Spanish music theorist*Francisco Vidal Salinas, Chilean politician...
; offshore red mangrove
Rhizophora mangle
Rhizophora mangle, known as the red mangrove, is distributed in estuarine ecosystems throughout the tropics. Its viviparous "seeds," in actuality called propagules, become fully mature plants before dropping off the parent tree...
cays; black mangrove
Avicennia germinans
Avicennia germinans, commonly known as the black mangrove, is a species of flowering plant in the acanthus family, Acanthaceae.A. germinans grows in tropical and subtropical regions of the Americas, on both Atlantic and Pacific coasts, and on the Atlantic coast of tropical Africa, where it thrives...
forest; lowland pastures (dry coastal forest); suburban areas; coconut
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
plantations; and coastal cliffs. Building of the nest is performed solely by females while feeding of the young is performed by both sexes. Nestlings leave the nest 13 to 16 days after hatching. Males defend small territories, usually around 3 metres, during the nesting period. Before the nesting period males defend slightly larger territories to repel other males.
Yellow-shouldered Blackbirds engage in anting
Anting (bird activity)
In the behavior called anting, birds rub insects on their feathers, usually ants, which secrete liquids containing chemicals such as formic acid, that can act as an insecticide, miticide, fungicide, bactericide, or to make them edible by removing the distasteful acid. It possibly also supplements...
, a rare behavior only observed in the Puerto Rican Tanager
Puerto Rican Tanager
The Puerto Rican Tanager is a small passerine bird endemic to the archipelago of Puerto Rico. It is the only member of the Nesospingus genus of the tanager family....
among West Indian birds. Individuals were observed applying Pheidole
Pheidole
Pheidole is a genus of ant that belongs to the ant subfamily Myrmicinae.-The Genus:The genus Pheidole is widespread and ecologically dominant...
spp. ants to its body and feathers for a short period of time (8 min.).
The species engages in mobbing, a behavior in which a pack of birds, from one or more species, attack a known predator (usually to defend eggs or hatchling
Hatchling
In oviparous biology, a hatchling is the newborn of animals that develop and emerge from within hard-shell eggs. The offspring of birds are often hatched naked and with their eyes closed. The hatchling relies totally on its parents for feeding and warmth. Hatchlings precede nestlings in the chick's...
s).
Threats and conservation efforts
Ceiba, Puerto Rico
Ceiba is a small town in northeast Puerto Rico. It is named after the famous Ceiba tree. Ceiba is located in the east coast of the island, bordering the Atlantic Ocean, north of Naguabo, south of Fajardo, and east of Río Grande. It is located about one hour's driving distance from San Juan...
, an area expanding from Cabo Rojo
Cabo Rojo, Puerto Rico
Cabo Rojo is a municipality situated on the southwest coast of Puerto Rico and forms part of the San Germán–Cabo Rojo metropolitan area as well as the larger Mayagüez–San Germán–Cabo Rojo Combined Statistical Area....
to Guánica
Guánica, Puerto Rico
Guánica is a municipality in southwestern Puerto Rico located on southern coast, bordering the Caribbean Sea, south of Sabana Grande, east of Lajas, and west of Yauco. It is part of the Yauco Metropolitan Statistical Area....
in the southwest region of Puerto Rico, and a small area in San Germán
San Germán, Puerto Rico
San Germán is a municipality located in the southwestern region of Puerto Rico, south of Mayagüez and Maricao; north of Lajas; east of Hormigueros and Cabo Rojo; and west of Sabana Grande. San Germán is spread over 18 wards and San Germán Pueblo...
.
Diseases such as avian pox
Avipoxvirus
Avipoxvirus is a member of the Poxviridae family. The Poxviridae family is the family of viruses which cause the victim organism to have poxes as a symptom. This pox virus is one that affects birds only. Poxviruses have generally large genomes, and other such examples include smallpox and monkeypox...
have been associated with extinction of bird populations such as Hawaiian honeycreeper
Hawaiian honeycreeper
Hawaiian honeycreepers are small, passerine birds endemic to Hawaii. Some authorities still categorize this group as a family Drepanididae, but in recent years, most authorities consider them a subfamily, Drepanidinae, of Fringillidae, the finch family...
s. For this species only one type of parasite has been observed, the chewing louse
Chewing louse
Mallophaga is a suborder of lice, known as chewing lice, biting lice or bird lice, containing more than 3000 species. They have paurometabolis or incomplete metamorphosis....
(formerly classified as Mallophaga), with three species being observed: Philopterus agelaii; Machaerilaemus spp.; and Myrsidea spp. The parasites predominantly occur in the head area with adult males having the highest infestation percentage and juveniles having a lower infestation rate than adults. The mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s Ornithonyssus bursa and Anclrolaelaps casalis have also been observed in nests, but the information presently available does not indicate they are a threat. Another disease commonly experienced by Yellow-shouldered Blackbirds is fowlpox
Fowlpox
Fowlpox is a worldwide disease of poultry caused by viruses of the family Poxviridae and the genus Avipoxvirus. The viruses causing fowlpox are distinct from one another but antigenically similar, possible hosts including chickens, turkeys, quail, canaries, pigeons, and many other species of...
, also known as avian pox. Lesions caused by this disease occur in exposed areas such as the legs and the bend of the wings.
Nest predation has been an important contributor to the decline of the Yellow-shouldered Blackbird. Known terrestrial predators include rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s (Rattus rattus), mongoose
Mongoose
Mongoose are a family of 33 living species of small carnivorans from southern Eurasia and mainland Africa. Four additional species from Madagascar in the subfamily Galidiinae, which were previously classified in this family, are also referred to as "mongooses" or "mongoose-like"...
s and feral cats, all introduced species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
to Puerto Rico. Rats constituted the main nest predator eating both eggs and hacthlings. A 1983 report concluded that rat predation accounted for 48% of nest failures that year. The majority of the activity coincided with the recession of water from July to August which exposed the mangrove nesting area to dry land. Since the middle 1980s artificial PVC nesting structures have been created in mudflats surrounding mangrove forests to reduce rat predation. These structures replaced old wooden nesting boxes and were readily accepted by the species. Presently, few (1 to 2) natural nests are observed each year in the area.
The loss of feeding and breeding habitat and brood parasitism by the Shiny Cowbird
Shiny Cowbird
The Shiny Cowbird, Molothrus bonariensis, is a passerine bird in the New World family Icteridae. It breeds in most of South America apart from the most dense jungles, mountains and deserts , the coldest southernmost regions , and on Trinidad and Tobago...
are among other threats that limit and endanger the Yellow-shouldered Blackbird populations. Natural predators, such as the Pearly-eyed Thrasher
Pearly-eyed Thrasher
The Pearly-eyed Thrasher is a bird found in Puerto Rico and the Virgin Islands, the Bahamas and Antilles. Its genus, Margarops, is considered monotypic today; formerly the Scaly-breasted Thrasher was placed here too...
(Margarops fuscatus), also represent a threat, although minor, to the populations. These animals have been reported to steal eggs and young from nests and to also destroy or steal nesting materials which in many cases leaves the young as prey for the predators.
See also
- Fauna of Puerto RicoFauna of Puerto RicoThe fauna of Puerto Rico is similar to other island archipelago faunas, with high endemism, and low, skewed taxonomic diversity. Bats are the only extant native terrestrial mammals in Puerto Rico. All other terrestrial mammals in the area were introduced by humans, and include species such as cats,...
- List of endemic fauna of Puerto Rico
- List of Puerto Rican birds
- List of Vieques birds
- El Toro WildernessEl Toro WildernessEl Toro Wilderness is a National Wilderness Preservation System located partly within El Yunque National Forest on the island of Puerto Rico...