Guano boobies
| Guano boobies | ||||||||
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Guano Booby ( Sula variegata ) |
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| Scientific name | ||||||||
| Sula variegata | ||||||||
| ( Tschudi , 1843) |
The guano booby ( Sula variegata ), also known as the Peruvian booby , is a sea bird from the booby family . While the other species of this family have specialized in the use of food niches away from the coast, the bird , which occurs only on the Peruvian , Chilean and occasionally on the Argentine coast , uses the abundance of food that exists there through the Humboldt Current. The abundant supply of Anchoveta engraulis in normal years compensates for the fact that the gannet has to compete for food with the chilepelican and the guanocormorant , two other species of the order Suliformes. The large food supply also allows him to regularly raise several chicks. This also distinguishes it from the other booby species.
The El Niño weather phenomenon occurs every few years . During these years there is a different climate off the inhospitable coast of Peru; the cold and nutritious Humboldt Current stays away and with it the huge anchovy swarms on which the guano booby lives. During these years a very large proportion of the population regularly starves to death. This sharp drop in the population can be compensated for because so many chicks are raised in good years.
Appearance
Body measurements and weight
The guano booby weighs around 1,300 to 1,500 grams. Several species of the genus Sula are in a similar weight group. Only the. Red-footed booby with an average of about 900 grams is significantly lighter, while very heavy female of the masked booby can weigh up to 2,350 grams. The length of the wings is between 38 and 41 centimeters. The females are slightly larger than the males. The beak measures 9.2 to 10.1 centimeters from the forehead fletching to the tip.
Plumage and other anatomical features
Guano boobies have a white feathered head, neck and a white underside of the body. Your face mask is somewhat reminiscent of that of the gannet . Similar to this one, a featherless area of skin extends around the beak and from the end of the beak to the eyes, but here it is from dark gray to dark blue in color. The wings and back are feathered brown. The feathers have regularly white tips, especially on the back plumage. The birds appear slightly spotted.
The beak is gray-blue, sometimes the color is reddish to pinkish. The eyes are red-brown to dark orange. The feet and legs are gray to gray-blue.
Fledglings differ significantly from adult birds in their plumage. They have a gray to gray-beige plumage. The head and neck appear a little darker than the rest of the plumage. Similar to the young birds of the northern gannet, a guano gannet goes through two different moulting cycles at the same time.
voice
Guano boobies have an extensive repertoire of voices. There is a gender difference between the calls of the males and the females. In the intraspecific conflict, the male lets short, high-pitched shouts be heard. The female's calls fluctuate in volume and pitch. Her repertoire of sounds also includes grunts, trumpet-like calls and those that are reminiscent of the calls of geese.
Basically, the boobies that breed in colonies are not only able to recognize their partners and their young by their voice, but also to identify the birds that breed in the immediate vicinity. This presumably also applies to the guano boobies, which breed 1.5 pairs per square meter.
distribution
The guano booby breeds mainly on rock islands off the Peruvian coast. Some of its breeding colonies can be found directly on the mainland coast; one of them not far from Lima . In its southernmost distribution area, the guano booby reaches Chile and occasionally even Argentina .
The predominant part of its distribution area lies between 6 and 10 ° S and around 13 ° S. Within this distribution area it happens relatively often that colonies are given up and new ones established. In years when there is a lack of food due to the El Niño effect, guano boobies can also be found far outside this range. The bird can sometimes even be found inland. Well-known, large guano booby colonies include those on Isla Lobos de Tierra , Isla Lobos de Afuera and Isla Mazorca . In 1962 there were 750,000 guano boobies in Mazorca.
Duration
The population numbers of the Guanot Booby are subject to strong fluctuations. After a number of good, fish-rich years, colonies in which more than 100,000 boobies breed are not uncommon. The colony on Mazorca with its 750,000 birds is the largest known colony of guanot boobies.
The stock figures drop significantly in El Niño years. Tens of thousands of birds starve to death when the cold Humboldt Current reverses and the anchovies remain too deep to be reached by the guano boobies. The ability to raise several young birds helps to compensate for these populations within a few years.
The guano booby shares its specific habitat with the guanocormorant and the brown pelican . In contrast to the guanocormorant and the brown pelican, the fact that a very intensive fishery is now being carried out in this region has apparently less negative effects on the guanot booby population. This is possibly due to the fact that the gannet is able to reach deeper water layers by diving than its two food competitors. The guano booby apparently flies further in search of food than its other two species.
Food and subsistence
The guano booby is one of the types of booby that usually dive for fish with other conspecifics. However, it is not a matter of conscious cooperation, even if flocks of up to 1000 birds can dive synchronously with each other. This may increase hunting success as it makes it more difficult for the fish to avoid the birds' diving thrusts. In view of the large flocks, ornithologist Bryan Nelson wrote that it was amazing that the birds swimming on the surface of the water were not impaled by the falling birds.
Foraging flights of the exclusively diurnal guano boobies last between two and 12 hours. Their average diving depth is 15 meters. But they are able to reach a depth of 40 meters. You can stay underwater for up to a minute.
Systematics
The blue-footed booby is considered to be the type of booby that is particularly closely related to the guanot booby. Like the masked booby , these two species also have very specific territorial behavior. This also suggests a close relationship. The following cladogram follows the result of molecular analysis by Friesen and Anderson, who come to similar results:
| Sulidae (boobies) |
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literature
- J. Bryan Nelson: Pelicans, Cormorants and their relatives. Oxford University Press 2005, ISBN 0-19-857727-3
Web links
- Videos, photos and sound recordings of Sula variegata in the Internet Bird Collection
- Sula variegata inthe IUCN 2013 Red List of Threatened Species . Listed by: BirdLife International, 2012. Retrieved February 2, 2014.
Individual evidence
- ↑ Nelson, 2005, pp. 587f
- ↑ All dimensions can be found in Nelson, p. 588
- ↑ a b Nelson, 2005, p. 380
- ↑ Nelson, 2005, p. 129
- ↑ Nelson, 2005, p. 383
- ↑ Nelson, 2005, p. 380. Current figures are not available, but the number is probably not much smaller than it was then
- ↑ a b c d Nelson, 2005, p. 381
- ↑ Nelson, 2005, p. 141.
- ↑ Nelson, 2005, p. 11
- Jump up ↑ VL Friesen & DJ Anderson: Phylogeny and evolution of the Sulidae (Pelecaniformes: Aves): a test of alternative nodes of specification. In: Molecular Phylogenetics and Evolution 1997, No. 7, pp. 252-260