Topic : Land Birds
Article 9 10 December 2006
Narina Trogon – the large leaf-gleaner
Narina Trogon Apaloderma narina is just one of almost 40 trogon species that inhabit forested regions of the world, and unfortunately Africa is poorly represented by this particularly beautiful family of birds with only 3 representatives. Interestingly, the meaning of the generic name Apaloderma is ‘thin skinned’, a name given to the family because of the fact that it has very thin skin that tears easily when skinned!
Narina Trogons are essentially large forest leaf-gleaners that feed mainly on invertebrates and to a lesser extent on small vertebrates. A high percentage of prey brought to nests are smooth-skinned caterpillars from the moth, and not butterfly family. In southern African forests, it seems therefore that they are most dependant on moth fauna for prey.
Their hunting strategy is to perch in the mid-canopy and scan the nearby leaves and branches for prey, which apart from caterpillars may include spiders, dragonflies, moths, preying mantises, cicadas and small dwarf chameleons.
Prior to breeding, males gather together in the mornings in what is known as assemblages. Here in the absence of females they display by hooting vociferously, puffing their chests out and chasing each other about from tree to tree. Birds will displace the leader by flying at it and physically knocking it off its perch. After an hour or two of displaying they then return to their separate territories and team up again with the females.
Trogon nests are notoriously difficult to find. They nest in natural tree cavities and are very reluctant to approach nest holes when intruders such as humans are in the vicinity. To add to this, change-over of incubation duties only takes place twice a day because the female incubates during the night and through to about 09h00 – 10h00 when the male takes over and remain in the nest for the rest of the day, to be relieved by the female in the late afternoon again. Once the chicks grow they become very vocal when soliciting for food, and this is perhaps their Achilles heel because they call so loudly they can be heard almost 50 m away. This of course attracts predators, so the failure rate during nesting seems to be very high. Then there is also another very important factor that is to date undocumented. Narina Trogons will for some reason not enter small nest-hole cavities. For years I unsuccessfully placed large nesting boxes with 7cm entrance holes in the local forest hoping for one of them to be utilized by trogons. Then Guy Upfold found a relatively low nest with a large 15 cm entrance hole. To see if this would solve the problem, I increased the entrance hole size on my nest boxes from about 7 cm to 15 cm and 2 of the nest boxes were utilized that same season! The problem with large nest holes is they are more vulnerable to predation and easy penetrable by genet cats, hornbills and Harrier-Hawks (Gymnogene). Of the 5 breeding attempts I have monitored, only one has been successful.
Like wood-hoopoes, Narina Trogons are able when threatened to secrete an extremely foul-smelling liquid from the preen gland at the base of the tail, but the effectiveness of this anti-predatory liquid is unknown. I have handled adult male trogons (both mist-net caught birds and in a nest hole), and getting this liquid on your skin is not something I would recommend to anyone. It is extremely smelly and washing your hands with soap and water does not immediately solve the problem. I would imagine though that the rotten smell would be some sort of deterrent to a predator in the tight confines of a nest-hole. These nest cavities are in any case very smelly places. I have on a number of occasions handled trogon chicks (from day one) and they do not seem to have the ability to produce this protective secretion during the nestling period. Having never held female birds, I can only assume they, like the males, also have the ability to secrete this malodorous liquid.
On the whole, South African forests are fairly well conserved, but Narina Trogons are essentially birds of two different habitats. They occupy both forest and riparian woodland habitats and it’s the latter area where the problem lies. Much of the riparian fringing woodland in Africa (especially north of our borders) is sought after for the growing of crops, so degradation of gallery forest has affected trogon habitat through much of its distribution range. Also, in conserved areas with above normal populations of elephants, one should also not under estimate the impact of these populations on riverine fringing woodland, at of course the expense of species such as Narina Trogon.