Butorides sundevalliGalapagos heron(Also: lava heron)

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Geographic Range

Galapagos herons, also known as lava herons, are found only in the Neotropical region. They are endemic to the Galapagos Islands in South America and are not found anywhere else. They are commonly found on all of the islands in the Galapagos. (Castro and Phillips, 1996)

Habitat

Galapagos herons live and nest along the lava-rock coastlines, saltwater lagoons, and mangrove forests of all of the Galapagos Islands. (Castro and Phillips, 1996)

Physical Description

Adult Butorides sundevalli individuals are a uniform ashy-gray over the entire body. Males are slightly larger and more colorful than females, particularly during the mating season. The bill, 6.35 cm in length, is gray. The bills of males turn shiny black during the mating season. There is a crest on top of the head, which is shorter than that of most other heron species. Legs are normally gray, but during the mating season both female and male legs turn bright orange and the lores turn from green to bright blue. These are relatively small and compact herons. Juveniles are mostly brown in color, with streaking on the breast, a dark crown, and a grayish back. Juveniles are indistinguishable from juveniles of their close relative, striated herons (Butorides striata). (Castro and Phillips, 1996; Grant, 1986; Harris, 1974; Swash and Still, 2000; Castro and Phillips, 1996; Grant, 1986; Hall and Heinzel, 2000; Hancock and Kushlan, 2005; Harris, 1974; Kushlan, 1983; Swash and Still, 2000)

  • Sexual Dimorphism
  • male larger
  • male more colorful
  • Range mass
    193 to 235 g
    6.80 to 8.28 oz
  • Average length
    35 cm
    13.78 in
  • Average wingspan
    63 cm
    24.80 in

Reproduction

Males advertise by vocalization, and may perform circle flights and pursuit flights until they attract a female. When a female arrives, the males stretch, bow and coo. The female remains about one meter away from the male and does the same. They also poke each other with their bills and preen their wings, chest, and back. However, reproduction does not necessarily require these displays. Displays by lava herons are typically less elaborate and have less aerial activity than those of closely related species. Although not much is known specifically about lava heron mating, heron species tend to be monogamous. (Hancock and Kushlan, 1984; Hancock and Kushlan, 2005; Kushlan, 1983)

In general, the breeding behavior of lava herons is poorly known. The usual age at first breeding of closely related species is at about 2 years, although they may attempt to breed while still in juvenile plumage. Lava herons breed throughout the year, most often after heavy rainfalls that break droughts, and in the months from September through March. Before mating, both males and females cooperate to make a suitable nest of twigs; these nests are usually shallow and about 20 to 40 cm in diameter. Building the nest may take up to two weeks, and parents continue to maintain and improve the nest during the nesting period. Nests are solitary, except in areas with an abundance of food, where there may be two or three nests in close proximity. The nests are in the territory of the male and are usually built within 1 m of the ground in bushes, mangroves, or under rocks. They typically lay one to three eggs at a time and may mate up to three times per year, although survival rates may be low according to one study, in which only one of the chicks lived to adulthood. There is no recorded information on eggs of the lava heron, but eggs of closely related species are pale blue-green and average about 37 x 28 mm in size. (Hancock and Kushlan, 1984; Hancock and Kushlan, 2005; Harris, 1974; Kushlan, 1983)

  • Breeding interval
    Lava herons can breed up to three times per year.
  • Breeding season
    Lava herons breed year round, but mostly during the months of September through March.
  • Range eggs per season
    3 to 9
  • Range time to hatching
    21 to 22 days
  • Range fledging age
    34 to 35 days
  • Average time to independence
    14 days
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Eggs are incubated for 21 to 22 days by both male and female parents. After hatching, very little information is known on the parental investment of lava herons. However, in the closely related striated heron, hatching is asynchronous and may take 3 to 4 days. The chicks are born semi-altricial. They are covered with light gray down and have limited mobility. Parents feed the chicks by regurgitation. They can climb after one week, jump among branches after 15 days, and fly by 34 to 35 days. Both parents care for the chick until it leaves the nest, after about two weeks, but adult care appears to continue for some time after young have left the nest. (Hancock and Kushlan, 1984)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

While information regarding longevity of lava herons is scarce, the oldest known wild individuals from the same genus are recorded at 7.9 years for Butorides striata and 11.6 years Butorides virescens. There is no information on lava herons in captivity. (Clapp, et al., 1982; Clapp, et al., 1982)

  • Range lifespan
    Status: wild
    7.9 to 11.6 years

Behavior

Lava herons are primarily solitary animals. They are very territorial, a behavior which develops at an early age. They are also relatively sedentary, leaving their territories only to mate or forage. When other lava herons enter their territory, they will raise their crest and chase intruders away. However, they are not timid of most other species, and will even let humans approach as close as a foot away. This may be because they have evolved in isolation from predators, unlike their ancestors on the South American mainland. They tend to fly very little, preferring to walk. When lava herons do fly, their flights are low, short, and direct. When flying, their feet trail behind, displaying the brightly colored soles of their feet. (Hall and Heinzel, 2000; Harris, 1974)

Home Range

Lava herons have territories arranged linearly along the coastline, with individual territories ranging from 300 to 500 m in length. Territories can change over time. Size of a territory most likely depends on the amount of food available within the territory; one study found that territory size was inversely related to crab density. Each individual bird has his or her own territory. Nests are in the male territories. While mating, a female is allowed into the male territory, but she also appears to maintain her own territory. Females and juveniles are eventually kicked out of the male territory. (Kushlan, 1979; Kushlan, 1983)

Communication and Perception

Lava herons are a relatively quiet species and appear to be far less vocal than some similar species. When annoyed or distressed, lava herons emit a high-pitched "keyow" or "keuk." They also have specific, raspy territorial calls to frighten away invaders. Male vocalization in the form of "skow" calls also play a big part in attracting females. "Cooing" is an important part of the courtship ritual for both sexes. (Hall and Heinzel, 2000; Hancock and Kushlan, 1984; Hancock and Kushlan, 2005; Kushlan, 1983; Swash and Still, 2000)

Food Habits

Lava herons feed in the shore zone, from boats, on land, and in trees. They primarily eat small fish and crabs, but are also known to eat lizards, insects, prawns, and some small birds. In many cases, they will bite off just the legs of crabs and eat these while the crab runs away. They have been recorded catching crabs at a rate of 2 to 3 crabs per minute. Occasionally, they may eat eggs or chicks of various finch and mockingbird species. They do not typically seek out the other birds as prey but will strike at one if it happens to wander by while the herons are searching for food. Because some of their prey, like crabs, take a long time to eat, lava herons often lose food to lava gulls, Galapagos hawks, and frigatebirds. (Grant, 1986; Hall and Heinzel, 2000; Hancock and Kushlan, 1984; Hancock and Kushlan, 2005; Harris, 1974; Kushlan, 1979; Kushlan, 1983)

Lava herons feed at all tide levels. To catch their food, they will crouch stealthily and stab at unsuspecting prey in the water or on land, or they can dive for fish. They walk extremely slowly (as slow as 1 m per min) in shallow water, in branches, or on the shore. They sometimes rake their feet across the ground in search of food. It is possible that lava herons, like many closely related species, also use baiting techniques to catch prey. Individuals typically have their own favorite places to forage and, instead of covering a large area, fly between these smaller places. Individual birds also tend to have their own preferred prey and feeding behaviors. (Grant, 1986; Hall and Heinzel, 2000; Hancock and Kushlan, 1984; Hancock and Kushlan, 2005; Harris, 1974; Kushlan, 1979; Kushlan, 1983)

  • Animal Foods
  • birds
  • reptiles
  • fish
  • eggs
  • insects
  • terrestrial non-insect arthropods
  • aquatic crustaceans

Predation

Adult lava herons do not have many predators in the Galapagos. They are sometimes preyed on by magnificent frigatebirds (Fregata magnificens). For most bird species on the Galapagos Islands, invasive species pose the most serious threat to eggs and hatchlings. Black rats, feral pigs, and fire ants attack and eat bird eggs and hatchlings. Introduced cats may prove a threat as the birds have not developed a fear of cats. Lava herons have a coloration that closely matches the gray basalt rocks on which they live and nest, which can provide some protection from predators. They also produce alarm calls that may frighten off predators or alert nearby herons of danger. (Castro and Phillips, 1996; Eilperin, 2006)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Lava herons are important predators of crabs and fish and most likely help to keep these populations in check. Lava herons themselves are not often preyed upon, but this bird species does sometimes provide food for other species. Lava herons are not known to take part in any parasitic or mutualistic relationships. The species does, however, appear to have commensal relationships with Galapagos penguins and California sea lions. By flying in front of the penguins and sea lions swimming near shore, lava herons apparently increase their food capture rates. (Kushlan, 1979)

Mutualist Species

Economic Importance for Humans: Positive

Lava herons are among the many unique island species that attract ecotourists to the Galapagos Islands.

Economic Importance for Humans: Negative

There are no known adverse effects of Butorides sundevalli on humans.

Conservation Status

Lava herons appear to be common on the Galapagos Islands, but population sizes are mostly unknown. Illegal fishing and destruction of mangroves by shrimp farming may pose future threats to this species. On the IUCN red list, Butorides sundevalli and Butorides striata are listed together as "least concern." (Hancock and Kushlan, 1984)

Other Comments

Butorides sundevalli was previously considered a subspecies of striated herons, Butorides striata. They are indistinguishable in the juvenile form, and in addition, some adult lava herons have a greenish back and streaked neck, which may be a polymorphism, a result of interbreeding, or evidence of recent divergence. (Hall and Heinzel, 2000)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Elizabeth Chenoweth (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Castro, I., A. Phillips. 1996. A Guide to the Birds of the Galápagos Islands. Princeton, NJ: Princeton University Press.

Clapp, R., M. Klimkiewicz, J. Kennard. 1982. Longevity records of North American birds: Gaviidae through Alcidae. Journal of Field Ornithology, 53: 81-208.

Eilperin, J. 2006. "Invasive Species Threaten Galapagos Diversity" (On-line). Accessed November 11, 2006 at http://www.galapagos.org/news/03_2006_invasivespecies.html.

Grant, P. 1986. Ecology and Evolution of Darwin's Finches. Princeton, NJ: Princeton University Press.

Hall, B., H. Heinzel. 2000. Galapagos Diary. Los Angeles, CA: University of California Press.

Hancock, J., J. Kushlan. 2005. The Herons. New York: Oxford University Press.

Hancock, J., J. Kushlan. 1984. The Herons Handbook. New York: Harper & Row.

Harris, M. 1974. A Field Guide to the Birds of Galapagos. New York, NY: Taplinger Publishing Co., Inc.

Kushlan, J. 1983. Pair formation behavior of the Galapagos lava heron. Wilson Bulletin, 95: 118-121.

Kushlan, J. 1979. Foraging Ecology of the Lava Heron. Report, Estación Científica Charles Darwin, Puerto Ayora, Ecuador: 1 - 6.

Swash, A., R. Still. 2000. Birds, Mammals, & Reptiles of the Galápagos Islands. New Haven, CT: Yale University Press.