Curiouser and curiouser: Brown-backed Honeybird displays

ABOVE: The Brown-backed Honeybird probably ranks among the most B of LBJs. Despite their nondescript appearance, these mysterious little parasites guard many intriguing secrets. Shown here is the adult (left) and juvenile (right). Illustration by Faansie Peacock.

As a young birder growing up in the suburbs of Pretoria, South Africa, I usually spent September school holidays exploring my local patch – a 90 hectare piece of unfenced bush in a pleasant valley below my house. Today the area is designated as Moreleta Kloof Nature Reserve, and is a well maintained suburban protected area, with neatly laid out footpaths, a bird hide, toilets, introduced antelope, and a permanent gate guard. Back in the ninenties this was wild country – or as wild as you can get in a suburb. No fences, no facilities, no rules. Just meander down the slope after school, and start scratching around in the rocks, climb a tree or even cool down in the little stream. I even occasionally visited at night – and found some good stuff including two Buff-spotted Flufftails, European Nightjar and African Grass Owl, as well as mammals such as SA Hedgehog and Lesser Galago.

During windy August days and more balmy September weather, I became acquainted with a extremely nondescript little brown job known then as a Sharp-billed Honeyguide. Today you will know it as a Brown-backed Honeybird. International readers may know it as Wahlberg’s Honeybird. All these names refer to Prodotiscus regulus – probably one of our most easily overlooked bird species. Initially I thought that I had discovered a population of a very rare species, but as my exploration circle widened, I learned that honeybirds can actually be remarkably common in suitable habitat. What exactly constitutes suitable habitat is a good question, as this species occurs in a wide variety of wooded vegetation types. They seem to like hilly areas, and are often common in valleys or along ridges with medium-sized trees (but will also forage quite low down in scrubby bushes). I’ve often found them at particularly high densities in wooded kloofs and ravines, or on hillsides with broken woodland within areas otherwise dominated by grasslands. They seem to like broad-leaved woodlands more than thornbush, and I don’t really associate them with pure acacia-type woodlands.

They may also be encountered along forest edges, or in association with alien trees, such as wattles that provide the birds with tiny, waxy scale insects on which they feed. This requires some explanation. Honeyguides and honeybirds are among the only birds that can digest wax, with the aid of enzymes secreted by bacteria in their digestive tracts. In the larger honeyguides this is where the association with bees come in. In the smaller honeybirds, wax is obtained from scale insects and woolly aphids. The birds can sometimes be seen delicately picking these small bugs from leaves and twigs. Honeybirds lack the raised nostrils of the larger honeyguides, and smell probably plays a less important role in finding their food.

Their ability to adapt to alien trees, such as wattles, has allowed them to increase their range in the last few decades. Previously the species occurred only as far south as Port Elizabeth, and it was only recorded in the Western Cape for the first time as recently as 1986. Judging from the map below, they are clearly expanding their range considerably in in this province.

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ABOVE: This map from SABAP2 (South African Bird Atlas Project; website here) shows the strangely fragmented distribution of the Brown-backed Honeybird in South Africa, at 5′ x 5′ pentad scale. The blue and purple squares indicate high reporting rates; the green and yellow show where the species is uncommon. Brown-backed Honeys are widespread throughout the old ‘Transvaal’ province in the north of the country, but the species is clearly more common on the central high-lying areas (which are predominantly in the grassland biome) than in the subtropical woodlands of the lowveld and Limpopo River Valley. The species avoids dry, sandy, Kalahari woodlands. In KwaZulu-Natal, it also avoids the wet subtropics of Maputaland and Zululand, but occurs up to high altitudes in the Drakensberg foothills. The map shows curiously isolated centres of abundances: 1) in Gauteng (which is partly explained by the many birders living there); 2) the escarpment region of Mpumalanga; 3) around Vryheid in KwaZulu-Natal; and 4) in the midlands of KwaZulu-Natal. The two isolated records in the central part of the country are from the cities of Kimberley and Bloemfontein respectively, where irrigated gardens and stands of alien trees may explain its presence. The extension along the coast west of about Port Elizabeth is a recent phenomenon.

Although honeybirds are year-round residents, I become especially aware of their presence in August and September each year, when they perform their remarkable display flights with particular gusto. In fact, to me they have become a harbinger of spring. Listening for birds displaying overhead is undoubtedly the best way to locate honeybirds. During their high speed aerial chases, they utter a unique, piercing and quite far-carrying sound that is hard to describe. It is a single, sharp insect-like tzick! note that is repeated every 1.5 seconds. During the display one bird chases another, keeping right on its quarry’s tail, and expertly mirroring its evasive maneuvers at breakneck speeds, all the while executing deep dips or undulations. Once you train your ears to listen for their distinctive calls, one soon realizes that Brown-backed Honeybirds can be locally abundant. In the Wilge River Valley north of Bronkhorstspruit, I once counted 12 birds in a morning, for example.

Why are they so easily overlooked? Certainly not because they are shy, as they almost always perch on dead twigs right at the very top of trees where they are quite conspicuous. They are also quite tame and approachable. Nevertheless, they are small (see images below), reserved, generally quiet and exceptionally dull in appearance. Really the only plumage feature that is worth mentioning, is that, like other honeyguides, they have white panels on most of their tail feathers. These white areas are visible when the tail is seen from below, or when it is partly spread. A good structural feature to look for is the uniquely shaped bill: a thin black spike that is noticeably curved downwards.

ABOVE: Conveniently, I happen to have a Brown-backed Honeybird in my freezer that was found dead in a Johannesburg garden. These images show how small the species really is (compare R1 coin). The white tail panels are visible – otherwise the bird is extremely nondescript (perhaps for a reason!). Note that this is definitely not the normal natural posture of the species, but rather a result of my cramped freezer.

This morning I visited Roodeplaat Dam Nature Reserve, just north-east of Pretoria to take advantage of the unseasonably warm weather. I stopped at a little bridge in an area of broken woodland, and became aware of a strange sound that I couldn’t place. The culprit? You guessed it – a Brown-backed Honeybird. Perched on some dead twigs at the top of a nearby 5 m high tree (i.e. in the usual spot), I spotted two honeybirds about 1 m apart. The birds were giving a hoarse chew call every few seconds. Both birds were also incessantly flicking (both) their wings open very briefly, and at the same time slightly depressing (ticking) their tails. They flicked their wings on average every 5 seconds or so, but at times as fast as once every second. Often the wing flicking seemed to be synchronized between the two birds. I assumed that this may be a form of courtship display between a male and female, but they were soon joined by a third bird, which was promptly chased around the treetops in the typical dipping fashion, accompanied by similar but more excited calls i.e. w’chew, w’chew, w’chew... They also uttered short chattering trilled calls, prrrt, prrrt, like a crombec or firefinch. The interaction continued for at least five minutes before the birds moved off. Several other pairs were seen elsewhere in the reserve during the course of the morning.

As far as I can tell, this wing-flicking display and the hoarse chew calls have not been described in the literature. There is mention of a female making a canary-like tseeeu tseeeu, and also of rasping zeet-zeet calls, but I’m not sure if these descriptions pertain to the same type of sound that I heard. I should also mention that the ‘song’ of Brown-backed Honeybirds is a rather harsh, dry trill lasting 3-4 seconds, somewhat like a cross between a cicada and Crested Barbet. This is usually given by single birds while perched.

The similarity of honeybirds and small brown flycatchers has been pointed out many times in field guides. Indeed, the specimen in my freezer was originally identified as a flycatcher by the person who found it. At a glance, the Brown-backed Honeybird is remarkably similar in size, shape and colour to the Spotted Flycatcher, a very common non-breeding migrant from the Palearctic with which it shares its habitat in the summer. This similarity was enhanced by the quick wing flicking – a characteristic behavioural quirk of Spotted Flys.

Perhaps the resemblance between honeybirds and flycatchers is incidental, but perhaps not… Being brood parasites (of cisticolas and prinias and probably other cisticolids with spherical nests), it may be beneficial for the parasitic honeybird to resemble a harmless flycatcher, in effect, allowing it to hide in plain sight, and avoid persecution or suspicion of its hosts. This is pure speculation, but perhaps this is another instance of aggressive mimicry, as with parasitic cuckoo finches mimicking red bishops (see blog post here). Let me know what you think!

ABOVE: Having a scratch. Whether birds scratch their heads over or under their wings has been used as a classification criterion. In this image you can make out the zygodactyl toe arrangement of honeybirds, with two toes pointing forwards, and two backwards. Photo by Phil Penlington.