Monday, 24 October 2011

Sugarbirds are SWEET!

When I first moved to Blue Hill Escape and was exploring options for opening hiking trails, I was amazed by how many Cape Sugarbirds there were. The males would give their trilling display calls down the valleys, tails streaming like banners behind them. The trail I opened up I called Sugarbird Valley as a result. That was in April 2010, it was a drought year. By November, walking that trail, one was lucky to see any Sugarbirds at all. The proteas had stopped flowering, and the sugarbirds had moved on. I was not aware of any other patches of flowering Proteas around Baviaanskloof, or even seen any in the Prince Alfred's Pass through the Outeniqua mountains on the way to Knysna. So where had all the Sugarbirds gone to? None of the bird experts I asked could give me a satisfactory answer as to the extent of the bird movements.

Apart from Roberts Birds of Southern African VIIth edition, the other place to seek out information on birds is the The Atlas of Southern African Birds and the SABAP2 website. According to the Atlas, the longest movement record for a ringed sugarbird is 160km, but no average is given. It is noted that sugarbirds, like most nectarivores, are resource trackers – so they move in response to food availability. Sugarbirds specialize in feeding on a variety of protea species and these mostly flower during the winter months. What they do during the summer months, when few or no proteas are flowering, is poorly understood.

Protea eximia pollen results in the purple coloration around the forehead of this Cape Sugarbird
SABAP2 is particularly interesting as it allows one to compare the atlas conducted largely in the 90s with the atlas being conducted at the moment. Most of the Fynbos occurs in the W. Cape, which allowed me to easily count up the quarter degree grid squares where sugarbirds had been recorded during the two atlases. I was alarmed to find that the number of quarter degree grid cells where sugarbirds are found has decreased by 18%. By way of comparison, Malachite Sunbirds, which also feed on proteas in Fynbos but are generalist nectarivores and so not tied to proteas in the same way, have only shown a 10% percent decrease in reported range. Still, this decrease is not as bad as for two Fynbos endemics: the Protea Seedeater (down 48%) or Cape Rockjumper (also down 48%), where the decrease in range and the increase in fragmentation is cause for serious concern. In fact, in my opinion these species should no longer be classified as Least Concern as they approach IUCN Vulnerable status under both range criteria (<20 000km2 coupled with fragmentation) and decrease in relative abundance of >30% in a period of 10 years.

Cape Sugarbird distribution at the Quarter Degree Grid Cell level - grey  cells are the reported range from the previous Atlas and far outnumber red, which represents expansion in reported range.
As such, with most of Blue Hill Escape consisting of mountain fynbos (with lots of proteas), and since I have recorded all the Fynbos endemic bird species here, this is now the area I am focusing my research attention. Luckily, my cause has been recognised by Phoebe Barnard at the South African Biodiversity Institute (SANBI), who has signed me on as a postdoctoral researcher. Phoebe's research focuses on the impacts of climate change on the Fynbos avifauna.

So, what have I learnt about Cape Sugarbirds so far?

While training to be a ringer, Mike Ford showed me that the most reliable way to tell male from female adult Cape Sugarbirds is actually not in the tail – which can be short in males after a moult, but actually in what is known in the 'paddle' of the 6th primary feather in the wing. This apparently makes the rattling whistle noise during the male display flight.

The 'paddle' of the sixth primary of a male Cape Sugarbird wing
Primary feathers of a female Cape Sugarbird
Second, the tongue of the sugarbird is an amazingly delicate bottle-brush. This must act as a kind of sponge to help get the nectar from the protea flower nectaries, which are buried deep within a mass of styles and stigmas.

Sugarbird tongue
Thirdly, sugarbirds have extremely sharp and powerful claws, given their size. I've been told this is so that they can hold onto swaying protea flowers in strong winds – but other nectarivores like the sunbirds seem to do fine with a 'normal' claws. From experience, the claws are stronger and more capable of piercing flesh in the male sugarbirds, and I suspect that these are weapons with which male sugarbirds defend their patch when their display flights don't have the desired affect on rivals. However, I am not aware of any lethal battles being recorded for this species by other researchers, so we'll have to see if I can prove that theory.

Ouch! wounds on my finger after a good haul of sugarbirds
We have 5 Protea species on the property. The most abundant, Protea repens, started the flowering season this year at the end of January and ended around April. Then Protea lorifolia came into flower (small numbers) and then Protea punctata and abundant Protea neriifolia from May or so, peaking in August. During this period I had the massive sugarbird captures (60 in one day!). Now Protea eximia is flowering and this protea is found only high up in the mountains in small stands – about 5 hectare patches as opposed to the 50 hectare or larger slopes for the P. repens and P.neriifolia. Where will they go after the P. eximia has stopped flowering is the big question. How far are they travelling? How vulnerable are populations now in our human modified landscape? How many sugarbirds are left in the fynbos? These and many other questions I hope to answer in the course of the next few years, with lots of ringing and point count surveys.

This study will take me across the range of mountain fynbos, from the Cedarberg to the Cockscomb. I can't wait to get started.

off to the office
Perils of the job. Nervous moments as this is NOT A SAFE POSITION TO BE IN!
Nets are up. Luckily they had been up before the wind and sun.
Cape Grassbird - although not a Cape Endemic, it is a southern African endemic. Their musical calls liven the hillsides.

1 comment:

  1. A fascinating and informative posting Alan. People on the ground, often ringers, spot changes that are tasking place long before the experts get to write it up. But also changes are taking place so rapidly that you are right to draw attention to anything you see. Good luck with the project. Love that little Grassbird!


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