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This is from an article I wrote that was published in Africa Birds and Birding April 2003 Vol.8, No.2.

Olive-headed Weaver Revealed

Text and photographs by Johann Grobbelaar

I'm staring at a nest 12 meters up a tree. The scary part is that I am at eye-level with it … not very comforting unless you're used to being at a height equivalent to that of a four-storey building. Sweat is running into my eyes as I peer through the viewfinder. It's hot outside, but that's nothing compared to the heat trapped within my small hide. Not even the honey bee that has just crawled down my sock into my right boot can distract me.
I have watched this nest for at least 20 hours in the past four days, hoping for another split-second glimpse of a little yellow bird. What kind of a weaver is this anyway? Weavers should be hanging from their nests, displaying extravagantly for all to see - and providing marvellous photographic opportunities. What is wrong with this bird?
A few things come to mind. Firstly, to the best of my knowledge there are as yet no decent published photographs of this bird - and the reason for that has become obvious. Secondly, these birds are monogamous and once a strong pair-bond has been established there is no need for the male to flagrantly advertise his position to potential predators (or photographers).
When we think of the ploceid weavers we envisage noisy, mostly yellow birds that breed colonially, with males whose bright breeding garb changes to a dull eclipse plumage in winter, and this holds true for most of the southern African weaver species. But the Dark-backed (Forest) Ploceus bicolor, Olive-headed P. olivaceiceps and Spectacled weavers P. ocularis are exceptions. In these species the females closely resemble the males, which have no eclipse plumage.
The Olive-headed is without doubt the least known weaver in southern Africa. It was first recorded in the region when M.O.E. Baddeley of the Durban Museum collected a specimen at Panda, southern Mozambique, in 1960. Phillip Clancey and Walter Lawson were also part of the Durban Museum's ornithological expedition and in 1961 Clancey described the Olive-headed Weaver as a species new to southern Africa. He returned to Panda in 1966 and bagged a further 23 specimens, reporting that they were easily collected and that he could have gathered more, which leads one to assume that the birds were plentiful. The birds were also seen at Muanza in the Sofala province of Mozambique (Clancey 1968).
The civil war in Mozambique thwarted any meaningful follow-up expeditions until the early 1990s. In a paper in Ostrich, March 2001, researchers Daniel B. Nuttall and Vincent Parker stated that the Panda population was the only one known to them and estimated it to be 100-200 birds strong. According to them, the species has not been located elsewhere in Mozambique for nearly 30 years. (See also Africa - Birds & Birding, vol. 3, no. 1.)
Several groups of birders have passed through Muanza in recent years but the weavers have yet to be recorded there. Peter Ryan reported heavy logging in this area in 1995 (African Wildlife, 49 (6): 18-19) and the birds may by now have disappeared from the area as a result of habitat loss.
Deforestation does appear to be the major threat facing this species. When we first visited the Panda area in October 1998 the destruction was obvious, with many of the tall, nest-bearing trees having been ring-barked. On a return visit to the same location in July 1999, slash-and-burn practices were rife and almost all the tall miombo in the vicinity had been destroyed. We did, however, manage to locate one pair of Olive-headed Weavers in this area.
On our visit in September 2002, we were shocked to find the miombo where the birds had previously been located replaced with subsistence slash-and-burn agriculture, and that cashew trees were growing instead of the miombo vegetation. A new road was under construction and we had to travel 13 kilometres west before we encountered suitable habitat. But this stretched for only six kilometres before it too gave way to a more open area with a great deal of farming activity.
In 1999 Vincent Parker estimated the remaining miombo at Panda to be 1 000 square kilometres in extent; of this area, only approximately 100 square kilometres was considered to be suitable for the Olive-headed Weaver. The destruction of its woodland habitat was reported to be ongoing.
The Olive-headed Weaver is found only in tall Brachystegia woodland that has a canopy of around 15 metres and taller. There is a strong relationship between the birds and the old man's beard lichen (Usnea species) which grows in these trees. Unfortunately it appears that it is these taller trees which are specifically targeted and felled by the local people, so although many patches of miombo remain, they lack the taller trees and the weavers have deserted them.
Olive-headed Weavers are monogamous and we found them in pairs during our week of observation during the breeding season. The pair-bond was strong, with the male often feeding the female. Our previous visit during July had also yielded a pair that foraged together and we surmise that the pair probably remain together throughout the year. They are active birds but fairly unobtrusive, feeding from mid-level upwards in the tall miombo. The birds move along the branches in a circular fashion, gleaning insects from the bark and concentrating in particular on the Usnea lichen. They often hang upside-down when feeding, a behaviour they share with both Dark-backed and Spectacled weavers. Interestingly, their foraging movement is not always upwards and they were sometimes seen working their way down a tree before they moved off to the next one. Once in a suitable area, the birds spend much time gleaning in each tree before flying off some distance to a new feeding ground. They are slender-billed and insectivorous and were never seen to come down from the trees to feed.
The male we saw could be easily distinguished by his yellow crown and olive-green face and chin. Although Clancey described the Panda race, P.o. vicarius, as being distinctive, with the yellow crown extending down the nape on to the mantle as a yellow 'V', the bird we photographed did not show this feature clearly. The female is more aptly named, as her whole head and mantle are olive-green. Both sexes show the orange-brown patch on the lower throat and upper breast, but this feature is more prominent in the male. The underparts are bright yellow, the wings greyish black. The tail is relatively short - shorter than is depicted in most of the popular field guides.
We found the best way to locate them was by their high-pitched 'tseeeee-weet-weet' call. The first syllable is at a high frequency, similar to that of the White-breasted Cuckooshrike, followed by two shorter and lower notes. A soft chattering was occasionally given but this was infrequent, even at the nest; unfortunately most field guides describe the call only as a loud chattering, which gives the impression that the birds can easily be located by this.
Its breeding in southern Africa was first recorded as recently as 1996. The nest is woven exclusively from Usnea lichen and situated in a mid-branch position; in this the Olive-headed differs from most other weavers (including Dark-backed and Spectacled), which construct their nests at the end of a thin twig. The general size and shape of the Olive-headed Weaver's nest is similar to that of Spectacled and Dark-backed weavers. The latter also use Usnea for their nests, but only for lining. The nest we photographed was situated on the south-western side of the tree, 12 metres up, approximately three metres from the canopy. We positioned our photographic hide some distance from the nest and the birds appeared unperturbed by its presence. The male even made a close approach to inspect the building of the tower. Trees with sparse foliage and heavy lichen are preferred, as the nests blend well with the surrounding lichen. Because the lichen remains green it is difficult to tell active nests from those used in previous seasons. Patient observation is the key to success.
The female did most of the incubation but our observations were hampered by the fact that the birds flew directly into the nest from a nearby tree, making it difficult to distinguish between the sexes. They wasted very little time in the vicinity of the nest and during the 20 cumulative hours we spent in the photographic hide, they presented us with less than 60 seconds in total of photographic opportunity. Once (during continuous four-day observations) the male was thought to have entered the nest for an incubation session that lasted approximately one and a half hours. The female would typically incubate for 30-50 minutes, after which the male would arrive and give the contact call. Often he would perch in the canopy some distance away, and occasionally he would then fly to the nest to feed her. Mostly, however, he would call repeatedly until she left the nest to go foraging with him, returning some 10-20 minutes later. After the chicks hatched, both parents fed them, although the female carried most of the workload.
In the recently published Threatened Birds of the World, BirdLife International has upgraded the classification of the Olive-headed Weaver to that of Near-threatened. Although there are fragmented populations in Malawi, Zambia and Tanzania, all of them seem to face the same difficulty as the birds at Panda, namely, habitat loss. In 1998 the total population was estimated to be about 20 000 pairs (Parker). They are nowhere common and as the majority of the populations of this species fall outside legally protected areas, there is a risk that the species may suffer a rapid decline in the future.
Persuading subsistence-level farmers who have no other means of support to change their way of living, without offering them a viable alternative, seems most unlikely. But until this can be done, the future of these birds in southern Africa seems bleak indeed.

The author would like to thank Theodore and Elize Theron for their unselfish support in helping to transport and erect the photographic hide. This included four near-arrests by the local police for alleged traffic violations. Without the Therons and my wife Lizet, these photographs would not have been possible.
To see the Olive-headed Weaver in southern Africa you need to travel to Panda, Mozambique. There is a reasonable gravel road leading there from both Inharrime and Maxixe and in the dry season a 4x4 vehicle is not essential. Once you've reached Panda, continue west along the main road - this is still under construction but it will eventually lead all the way to Xai-Xai, according to the locals.
At present, the patches of tall miombo start 13 kilometres from Panda on both sides of the road, but you may need to travel further in future…