ABOVE: The humble but characterful Yellow-throated Petronia, Gymnoris superciliaris. One could be forgiven for momentarily mistaking this for a semi-arboreal pipit. Petronias differ from typical sparrows in being more slender, long-winged and elegantly built, with thinner, more pointed bills and longer tails that are often wagged or flicked in true pipit-style. Petronias are equally at home in trees and on the ground, where they progress by a smooth walk or with short hops. This one appears to be moulting its outer tail feathers. Photo by Dylan Vasapolli / Birding Ecotours.
Since 2004, Bushwillow Estate on the shores of Vaalkop Dam, in North West Province, has been my home away from home. I pride myself on my 300+ bird list for the area, and I have had countless fun days exploring, studying birds, searching for nests, recording bird calls, sketching, climbing trees, herping and just generally whiling time away in the bush. What a privilege to have a little getaway in this corner of Africa!
However, even after all these years I still feel like I’m a visitor – while we might get out there once or twice a month at most, there is a myriad other residents in and around the house, who are there permanently. Moreau’s Tropical House Geckos stake their territories on the walls, a White-throated Monitor hangs around the garbage bins, and a Western Stripe-bellied Sand Snake has claimed his favourite tree. Under the deck is prime real estate – shared by a python, a family of warthogs, a rowdy crowd of Dwarf Mongooses and sometimes porcupines (which have a particular craving for plastic pipes). Bird-wise, any hollow or crevice in the house structure is sought after by White-throated Robin-Chats, which always choose some crafty little hideaway for their nests. Cape Wagtails nest in a potted plant, and we occasionally arrive to find a Barn Owl or Spotted Eagle Owl peering down at us from the roof beams. And that’s not even mentioning an endless variety of insects and arachnids.
We have a large outside umbrella over the splash pool. When we’re around we keep the fabric part slotted into the metal stand – when you open it in the mornings, a cascade of Cape Serotine Bats often tumbles out. When we leave, we remove and store the fabric part, leaving a nice hollow pipe. This spring, a pair of Yellow-throated Petronias decided that this metal pipe would be the perfect location to raise a family. We noticed the birds entering the pipe, usually carrying a feather, for several days. After some time we decided to have a closer look – while you couldn’t see much in the pipe, you certainly could smell something! A “rotten egg” smell of note wafted from the mouth of the metal pipe, and we came to the conclusion that something was definitely not right. Around that time the birds also seemed to abandon their nest site.
While it’s great to have a pair of petronias raising a family next to your swimming pool, it also means that we couldn’t use the umbrella at all. We had a similar problem when a pair of African Pied Wagtails that decided to build their nest inside our barge’s engine. So, with the help of a long piece of wire, I managed to extract some of the petronias’ nesting material. I say some because I couldn’t reach nearly all the way down, and I would guess at least half of the nesting material still remains. It appears that these birds have a particular passion for feathers. They had packed the pipe so densely with feathers that they effectively plugged it completely. The (definitely rotten) eggs were situated about 40-50 cm from the mouth of the pipe.
…these birds have a particular passion for feathers.
Pipes are not typical nest sites for petronias – though there are records of them breeding in metal fence posts and the like. Instead, they typically use an old woodpecker or barbet hole, or some natural crevice in a tree. In fact, they spend much time prospecting for such sites, and can often be seen thoroughly investigating cavities in dead wood or exposed snags. Furthermore, nest sites are typically less than 20 cm deep – this nest extended for at least 1.2 m into the pipe. Their preference for feathers as nest-lining is well known, but they may also use thread-like lichens, hair or wool. Interestingly, petronias as protective of their nest sites when other hole-nesters are near, though they pretty much ignore species that breed in open nests. Indeed, many studies have shown that the presence of suitable nesting cavities is often a more critical limiting factor to bird abundance than food or other resources. So think twice before chopping down a dead tree for firewood – these are arguably more important to avian communities than living trees! Ditto for a wide variety of other biodiversity.
ABOVE: This metal umbrella stand was chosen as a nest site by the pair of petronias. They filled the entire horizontal section with tightly packed feathers. By knocking on the pipe it sounded like the top third of the vertical piece was also filled; below this it was hollow except right at the bottom where presumably some debris had gathered.
ABOVE: The two rotten eggs that emerged from the tangles of feathers and other nesting material. Typical clutch size is 3-4 (range 2-5) in this species. These are incubated by the female only, but around 2-3 weeks. The eggs vary in colour and markings – these are towards the dark side of the spectrum.
ABOVE: The pipe was square-shaped and approximately 100mm x 100mm in size. The pipe was very hot to the touch and the temperature inside must have been unbearably hot. I suspect the temperature is what cooked the eggs as well. You can see Vaalkop Dam in the background (plus a knocked over ladder).
ABOVE: In addition to a multitude of feathers, this length of shed snake skin was also appropriated by the birds as nesting material. My herpetological knowledge is not quite up to scratch to identify the species, but I would guess perhaps one of the Psammophis snakes that live around the house.
These peculiar but charming little passerines are classified as sparrows (hence the old name Yellow-throated Sparrow), but they do remind me a lot of pipits. In fact, sparrows (Passeridae) and pipits (Motacillidae) are quite closely related. Petronias exhibit many pipitish characters: they spend a lot of time walking confidently on the ground, with a brisk pipit-like gait. When they flush, they fly up into the safety of a tree with a pipit-like call and a somewhat dipping flight. They look equally comfortable in trees and on the ground, and confidently walk along branches or glean insects among the foliage in a tit-like fashion. Petronias also have longish tails quite like pipits, which they dip or wag incessantly when concerned or excited. A major difference of course, is that petronias nest in trees whereas all pipits nest on the ground.
With experience the shape, movements and flight style of petronias render them a distinctive bird, but how would a beginner go about identifying this nondescript LBJ? Firstly, the yellow throat is NOT the way to go. This small yellow area is often invisible in the field and is best seen when the bird is singing. It also appears that juveniles lack this altogether. Instead look for the very bold white supercilium (eyebrow_ which extends all the way to the nape. There are few similar-sized brown woodland birds with a similar look in Southern Africa – but Streaky-headed Seedeater does spring to mind.
The taxonomy of petronias has been shuffled around a bit in the last few years. Firstly, the petronias are not in the genus Petronia. That honour is reserved for the Rock Sparrow Petronia petronia of Eurasia. I really enjoyed meeting these exquisitely marked, though not colourful, birds in the arid hills and gorges of southern Spain a few years ago. Anyways, the word Petronia is actually a Latin reference to rocks (as in the Apostle Peter – “the “rock” on which Christ built his church”). Petronius refers to the rocky mountainside habitat of the Rock Sparrow. Currently, four species of “petronias” are recognized; the alternative name bush-sparrow may be more appropriate for them. They are in the genus Gymnoris, which translates to “naked nose”. These are:
- Gymnoris superciliaris – our very own Yellow-throated Petronia, which used to be called Yellow-throated Sparrow (sometimes Southern Yellow-throated Sparrow). This species occurs widely across SC Africa, S of the equator.
- Gymnoris pyrgita – Yellow-spotted Petronia. The northern counterpart of our petronia, occurring in a narrow band across the Sahel region and more widely in NE Africa. It differs in being much plainer, lacking the pronounced super cilium and wing-bars of the Yellow-throated Petronia. In fact, it is more likely to be confused with another relative of the sparrows, the Pale Rock Sparrow Carpospiza brachydactyla.
- Gymnoris dentata – Bush Petronia. A bird of dry sparsely vegetated slopes of the Sahel. Looks a bit like a Grey-headed Sparrow, Great Sparrow and Petronia hybrid. Also notable for showing fairly pronounced sexual dimorphism, unlike other petronias.
- Gymnoris xanthocollis – Yellow-throated Sparrow (confusing) or Chestnut-shouldered (better). The only species to occur outside Africa; from Turkey to India.