Butorides sundevalli

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.

• Biogeographic Regions
• neotropical neotropical
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

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

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Aquatic Biomes
• coastal coastal

• Other Habitat Features
• estuarine estuarine

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 ).

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• male more colorful

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.

• Mating System
• monogamous monogamous

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.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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.

• Parental Investment
• altricial 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.

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.

• Key Behaviors
• arboreal arboreal
• terricolous
• flies
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial

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.

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.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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 .

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods

• 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.

• Anti-predator Adaptations
• cryptic 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.

Economic Importance for Humans: Positive

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

• Positive Impacts
• ecotourism ecotourism

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."

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.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

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.