I posted a similar query on the South African Bird Network in May 2005 after observing Dark-capped coupling with Cape in Addo Elephant NP. I got many replies which I have kept on file and paste below. I also was sent 2 scientific articles in pdf which if you PM me your address I can mail to you.
The correspondence on bulbul hybridization is as follows:
In the same vein as the recent discussion on prinias, on a recent trip to Addo Elephant National Park last week, I was intrigued to see a pair of bulbuls with one bird Cape and the other Dark-capped outside of my chalet. Both birds were adults and at first seemed agitated in each other's presence (making the typical bulbul social bubbling calls), but later perched on the same branch next to each other like a genuine pair. The next morning I saw another "mixed marriage" in the game viewing part of the park (several km from original sighting and unlikely to be same birds).
The red-eyed, Cape and dark-capped bulbuls are undoubtedly from a common ancestor, and can surely interbreed with only habitat preference separating them. Have any of the other SABN-netters come across interaction between these 2 species or their red-eyed relative. If previously observed, does anyone know what the dark-capped Cape offspring look like (or one of the other combinations)? What I am wondering is whether the white or red eye wattles are dominant or recessive genes?
there is a well-known hybrid zone of the bulbuls. As
far as I remember all 3 spp hybridise with each other.
Folks at Rhodes U have spent some time studying it.
Contact Adrian Craig in the Zoo Dept there - he should
be able to help you.
Raurie Bowie of the U of Stellenbosch said at a recent
talk that he's struggling to distinguish Cape from
Blackeyed genetically - they're basically the same.
Many years ago we used to get "Brown-eyed Bulbuls" at Abe Bailey Nature Reserve near Carltonville in what is now Gauteng. I remember reading something in the early 1980s about someone doing a study on the sibling bulbul species in the Eastern Cape I think. Richard Liversidge's name comes to mind, but I'm far from sure about that.
While staying at Betty's Bay last year I was very excited when I THOUGHT I had found a Cape/Red-eyed cross -- a bird in all other respects Cape Bulbul, but with bright orange eye-ring! Of course, I was soon disabused when I saw several other birds that had been feeding on the same aloe flower.
Thanks for the interesting news of Addo, which is a park I still look forward to visiting.
There is an excellent paper on the hybridisation between the bulbuls in the Eastern Cape by Penn Lloyd:
Lloyd, P., Craig, A.J.F.K., Hulley, P.E., Essop, M.F., Bloomer, P. & Crowe, T.M. 1998. Ecology and genetics of hyrid zones in the southern African Pycnonotus bulbul species complex. Ostrich 68: 90-96.
All the best,
Just a few more comments on species hybrids...
A few years ago I saw a pair of Bulbuls feeding fledged young in our garden (Lightenburg - Mafikeng area), one parent was Red-eyed and the other was Black-eyed, the offspring had reddish-brown eyes. This pair was observed breeding in our garden over a period of approx. two years.
Both bulbul species occur in this area, with Black-eyed more dominant in bushveld in the east towards Zeerust and Red-eyed, further west and south towards the Kalahari. On our farm there are however many "reddish-brown-eyed Bulbuls".
Cape White-eye and the recently split Orange-river White-eye also overlap on our farm and there are many intermediate birds (dark green with brownish flanks), but I have not seen evidence of hybridizing between these two species here. We also have a pair of Fiscal Shrikes, one with a white eye-brow ("Latakoo Fiscal"?), defending a territory together. In this area, the white eye-browed form is dominant in thornveld, while the normal form is dominant in the broad-leaved savanna and grassland.
We farm just outside Somerset East (3225DA) where some years back we recorded a blackeyed (as it was then) and a redeyed bulbul hybridising. The nest was about 3m above the ground in a large old oak tree in the garden.
I wrote a short article on this for the Bea-Eater, as at the time I recall the having been one or two other articles on the matter.
I often struggle with the bulbuls on the farm as what would seem to be a Black-eyed will suddenly become a wannabe red-eyed as it turns its head and catches some direct sunlight on the ring around its eye.
Incidentally Neil Turner who lives on a farm near Middleton (Somerset East district) has recorded all three bulbuls in a shrub in his garden. They also have all three bustards on their farm.
I hope you enjoyed my two cents worth,
Addo is a well known place for Cape / Blackeyed occurring together & inter-breeding (as is Sundays River Mouth). The main camp tends to have Blackeyed (presumably due to the trees) whereas the game area tends to have Cape. At Somerset East all three bulbul species occur togehter and inter-breed. Adrian Craig at Rhodes Univ has done work on them.
My limited observation of hybrids (Black - Cape and Black - Redeyed) is that the wattle is much smaller on the hybrids.
Dr Paul Martin
On my son's farm, just south of Heidelberg, situated on the Suikerbosrand River, both the Red-eyed and Black-eyed Bulbuls are present. The Black-eyed seem to be dominant, but there has definitely been hybridisation as one sees birds with reddish brown eyes. Here, in the NE Free State (Harrismith) we get only the Black-eyed, while the Red-eyed are found towards Bethlehem and Warden in the west and Golden Gate in the south. By the time one gets to Ficksburg they are all Red-eyed. I don't know if any one has noticed hybridisation towards those areas.