Sunday, 6 July 2014

Hornbills 4: Von der Decken's Hornbill

Von der Decken's Hornbill (male)
The only African hornbills in the collection are rather smaller than the species I have covered up to now, and occupy a very different environment. The Von der Decken’s Hornbill, Tockus deckeni, is an aridland species associated with thorn scrub and similar habitats in East Africa, along the rift valley from Ethiopia south into Tanzania. In this habitat food is harder to come by than in Asian rainforest, and they feed mainly on the ground, taking fruit, seedpods, insects, and small vertebrates. With such a large range, and a lifestyle that makes it a bird that is opportunistic when it comes to taking advantage of resources that must be variable in location and availability, they seem to be surviving well at present, and are evaluated as Least Concern by the IUCN. The most likely threats are destruction of potential nesting trees and habitat fragmentation.

As with other hornbills, the female is walled in by the male while incubating the 2-3 eggs. As the young grow, they require more food than the male can supply, at which point the mud seal on the nest is broken to allow the female to escape. The young and the adults then combine to seal up the nest entrance again until the young finally fledge. Outside the breeding season they are commonly seen in small flocks, probably combining parents and young.

Hornbills are intelligent birds, and Von der Deckens and at least one other species have been observed to take part in a mutualistic relationship with dwarf mongooses, Helogale parvula. The hornbills follow the foraging mongoose troop, no doubt feeding on any insects or lizards fleeing the troop (which can be up to 30 strong). The mongooses and hornbills reply to each other’s alarm calls, mostly for various raptors which might prey on either species, and adjust their guarding behaviour depending on what the other species is doing. The hornbills in particular warn of predators that threaten the mongooses but are no threat to themselves, showing that this is not just mongooses benefiting from the hornbills self-defence behaviour.

Dwarf Mongoose
At present, breeding of hornbills in captivity is rather intermittent, and productivity of the captive population of all species is very low. Given the long lifespans (20 years + even for smaller species) and small clutches, combined with the specialised breeding behaviour, this is hardly surprising, but if people are to see hornbills in zoos, let alone the wild, the success rate needs to be greatly improved. With better understanding of the physiology of the birds, especially the iron retention diseases I described in earlier posts, this will hopefully result in more baby hornbills being raised each year. For more on issues around hornbills, both in the wild and in captivity, see the hornbill section of the AZA Coraciiformes Taxon Advisory Group:

Next week, some new arrivals, and then I will move on to some of the inhabitants of Bug World that I have yet to cover.

(images from Wikipedia)

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