Dwarf alangans
| Dwarf alangans | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Collocalia troglodytes | ||||||||||||
| Gray , 1845 |
The dwarf salangan ( Collocalia troglodytes ) is a species of bird from the family of the sailors (Apodidae). With a body length of 9 centimeters, it is the smallest species of salangan . The species is endemic to the Philippines . The plumage is predominantly dark black-brown, on the rump it shows a narrow, strongly contrasting white stripe. The nesting sites of the dwarf alangans are located inside caves. Like many other salangans, it has the ability to echolocation, but it is the only species capable of this in the genus Collocalia .
features
Appearance
The body length is given as 9 centimeters, the wing length is between 86 and 96 millimeters. Dwarf alangans weigh between 4.5 and 6.8 grams, with an average of 5.4 grams. As a very small species of salangan, it is easy to identify with its dark, black-brown top and the narrow, but clearly contrasting white band in the area of the rump . Both on the wings and on the tail, the species shows the plumage typical of the genus. The underside of the wings and the tail are slightly lighter than the upper side, the middle and small arm covers are clearly the darkest plumage parts of the underside. The underside of the body looks very spotty, and especially between the upper abdomen and rump it is very light. Throat and upper chest area are gray-brown.
Most likely to be confused is the Zwergsalangane with almost as small sympatric occurring Glanzkopfsalangane . In some cases, representatives of this closely related species occurring in the Philippines show paler parts of the plumage in the area of the rump, but this still differs significantly from the strongly contrasting white band of dwarf salangans.
Vocalizations
The sounds of the dwarf salangans are described as a gentle chirping.
Since the nesting sites of the species can be located 30 meters inside caves, it has long been suspected that the species might have the ability to echolocate . This was confirmed in 2004. The dwarf alangana is the only representative of the genus Collocalia with this property. The dwarf salangan uses two clicks in the audible frequency range of humans at short intervals, so-called "double clicks", like most other echolocating salangan species, which are all assigned to the genus Aerodramus . At 16.9 milliseconds, the mean time interval between these two clicks is also in the same range as for the Aerodramus species.
distribution
The dwarf salangan occurs on almost all Philippine islands, including Palawan , but not quite in the southwest on the islands of the Sulu Archipelago . The species occurs very regularly in the lowlands, somewhat less often in the foothills. The dwarf alangane is a resident bird in the entire distribution area .
habitat
The species, which predominantly occurs in lower altitudes, is often found near inland waters . Away from the water, the dwarf alangana can be found above or near forests.
Behavior and food acquisition
Dwarf alangans are gregarious and can usually be seen in smaller groups.
Like all sailors, dwarf alangans feed on airborne insects and arachnids . They go in search of food at medium heights, and in forest areas they hunt directly above the treetops. In the more open terrain with only a few trees, they fly a little lower, but never directly above the ground. Syntopically occurring lettuce lanterns fly significantly lower when foraging for food. It seems that these are being pushed into this ecological niche by the competition of the dwarf alangans that are present at the same time , because in areas without these food competitors they obviously also occupy the middle altitude range.
Reproduction
The breeding season begins in July on Mindanao and in April on Bohol and Negros . Nestlings were sometimes observed in September. The nest is a flat, self-supporting half-shell that is attached to a cave wall or to the walls of irrigation tunnels. It consists of plant materials that are solidified with a significant amount of saliva. There were discussions about whether the nests belong to the " edible swallow nests ", which could not be clarified with certainty.
The clutch usually consists of two eggs, the size is 16 x 10 millimeters.
Systematics
Recent molecular genetic studies show that Glanzkopf- and Linchisalangane together the sister group to form the Zwergsalangane. All Collocalia species are therefore directly related and the genus would be monophyletic . The ability of dwarf alangans to echolocation, which has been proven since 2004, seems to contradict the molecular genetic findings, because this has so far only been observed in the Aerodramus species, which was also an essential criterion for the division of the salangan species into these genera. In addition, the click sounds used by the dwarf alangana for echolocation are very similar to those of some Aerodramus species. According to this, echolocation in salangans must either have been developed several times independently of one another or in some species, including the two other Collocalia species, must have been lost again. Neither seems particularly likely.
Subspecies are not differentiated in the dwarf alangana.
literature
- Phil Chantler, Gerald Driessens: A Guide to the Swifts and Tree Swifts of the World . Pica Press, Mountfield 2000; ISBN 1-873403-83-6
- Joseph del Hoyo, Andrew Elliot and Jordi Sargatal (Eds.): Handbook of the Birds of the World . Volume 5: Barn-owls to Hummingbirds . Lynx Edicions, 1999, ISBN 84-87334-25-3
Individual evidence
- ↑ This and all information not specially marked are taken from the following source: Chantler, Driessens: A Guide to the Swifts and Tree Swifts of the World . Page 126f, see literature
- ^ A b Charles T. Collins: Foraging of Glossy and Pygmy Swiftlets in Palawan, Philippine Islands. In: Forktail. 16: 53-55, 2000 ( online )
- ↑ Pedro C. Gonzales, Colin P. Rees: Birds of the Philippines. Page 73, Haribon Foundation for the Conservation of Natural Resources, 1988, ISBN 971-91113-0-5
- ^ J. Jordan Price, Kevin P. Johnson, Dale H. Clayton: The evolution of echolocation in swiftlets. In: Journal Of Avian Biology. 35: 135–143, 2004 ( online ; PDF; 1.9 MB)
- ^ Dioscoro S. Rabor: Philippine birds and mammals. Page 113, University of the Philippines, Science Education Center, 1977, ISBN 0-8248-0535-6
- ^ Thomassen et al .: Phylogenetic relationships amongst swifts and swiftlets: A multi locus approach. In: Molecular Phylogenetics and Evolution. 37: 264-277, 2005 doi : 10.1016 / j.ympev.2005.05.010