Sunbirds

The sunbirds and spiderhunters are a family, Nectariniidae, of very small passerine birds. There are 132 species in 15 genera. The family is distributed throughout Africa, southern Asia and just reaches northern Australia. Most sunbirds feed largely on nectar, although they will also take insects, especially when feeding young. Fruit is also part of the diet of some species. Their flight is fast and direct on their short wings.

The sunbirds have counterparts in two very distantly related groups: the hummingbirds of the Americas and the honeyeaters of Australia. The resemblances are due to convergent evolution due to the similar nectar-feeding lifestyle.¹ Some sunbird species can take nectar by hovering like a hummingbird, but usually perch to feed.

Description

The family ranges in size from the 5-gram Black-bellied Sunbird to the Spectacled Spiderhunter, at about 30 grams. Like the hummingbirds, sunbirds are strongly sexually dimorphic, with the males usually brilliantly plumaged in metallic colours.² In addition to this the tails of many species are longer in the males, and overall the males are larger. Sunbirds have long thin down-curved bills and brush-tipped tubular tongues, both adaptations to their nectar feeding.³ The spiderhunters, of the genus Arachnothera, are distinct in appearance from the other members of the family. They are typically larger than the other sunbirds, with drab brown plumage and strong down-curved beaks.

Species of sunbirds that live in high altitudes will enter torpor while roosting at night, lowering their body temperature and entering a state of low activity and responsiveness.²⁴

Distribution and habitat

Sunbirds are tropical species, with representatives from Africa to Australasia; the greatest variety of species is in Africa, where the group probably arose. Most species are sedentary or short-distance seasonal migrants. The sunbirds occur over the entirely of the family's range, whereas the spiderhunters are restricted to Asia.

The sunbirds and spiderhunters occupy a wide range of habitats, with a majority of species being found in primary rainforest, but other habitats used by the family including disturbed secondary forest, open woodland, open scrub and savannah, coastal scrub and alpine forest. Some species have readily adapted to human modified landscapes such as plantations, gardens and agricultural land. Many species are able to occupy a wide range of habitats from sea level to 4900 m.

Behaviour

Sunbird are active diurnal birds that generally occur in pairs or occasionally in small family groups. A few species occasionally gather in larger groups, and sunbird will join with other birds to mob potential predators, although sunbirds will also aggressively target other species, even if they are not predators, when defending their territories.

They are generally monogamous and often territorial, although a few species of sunbirds have lekking behaviour. Up to three eggs are laid in a purse-shaped suspended nest. The female builds the nest and incubates the eggs alone, although the male assists in rearing the young after hatching.⁵ The spiderhunters build cup-shaped nests, and both sexes help to incubate the eggs.⁵ The nests of sunbirds and spiderhunters are often targeted by brood parasites such as cuckoos and honeyguides.

Relationship with humans

Overall the family has fared better than many others, with only seven species considered to be threatened with extinction. Most species are fairly resistant to changes in habitat, and while attractive the family is not sought after by the cagebird trade, as they have what is considered an unpleasant song and are tricky to keep alive. Sunbirds are considered attractive birds and readily enter gardens where flowering plants are planted to attract them. There are a few negative interactions, for example the Scarlet-chested Sunbird is considered a pest in cocoa plantations as it spreads parasitic mistletoes.

Systematics

Gallery

References

^ Prinzinger, R.; Schafer T. & Schuchmann K. L. (1992). "Energy metabolism, respiratory quotient and breathing parameters in two convergent small bird species : the fork-tailed sunbird Aethopyga christinae (Nectariniidae) and the chilean hummingbird Sephanoides sephanoides (Trochilidae)". Journal of thermal biology 17 (2): 71-79.
^ ^a ^b Cheke, Robert; Mann, Clive (2008), "Family Nectariniidae (Sunbirds)", in Josep, del Hoyo; Andrew, Elliott; David, Christie, Handbook of the Birds of the World. Volume 13, Penduline-tits to Shrikes, Barcelona: Lynx Edicions, pp. 196-243, ISBN 978-84-96553-45-3
^ Cade, Tom; Lewis Greenwald (1966). "Drinking Behavior of Mousebirds in the Namib Desert, Southern Africa" (PDF). Auk 83 (1).
^ Downs, Colleen; Mark Brown (2002). "Nocturnal Heterothermy And Torpor In The Malachite Sunbird (Nectarinia famosa)". Auk 119 (1): 251-260. doi:10.1642/0004-8038(2002)119[0251:NHATIT]2.0.CO;2.
^ ^a ^b Lindsey, Terence (1991). Forshaw, Joseph. ed.. Encyclopaedia of Animals: Birds. London: Merehurst Press. pp. 207. ISBN 1-85391-186-0.

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