Wednesday, 4 July 2012

The great Swift debate!

I have just returned from a trip to western China, where I saw several hundred Common Swifts of the eastern pekinensis race. This was the first time I have knowingly observed this race of Common Swift and I managed to obtain quite a few photographs.

Common Swift Apus apus taken in the UK.

Common Swift Apus pekenensis
taken in western China.
Not that much difference between the races shown here! But there are small differences, which I will discuss later. Much of the literature on identification, seems to follow a set pattern, which may not be borne out by reality.
I am particularly interested in Common/Pallid Swift identification, as I live in the UAE, where Pallid Swift is common and Common Swift is an irregular spring & autumn migrant (but see my later note). To add to my interest, I have also spent a considerable period of time birding in Southern Africa, in particular in Zimbabwe and South Africa. Swift identification is not easy under any circumstances and my recent experience of pekinensis in China has lead me to revise some of my opinions. But let us step back a little and discuss the known distributions and migrations/movements of these two species:

Common Swift

Common Swift has two recognised races:
Apus apus apus & Apus apus pekinensis

A. a. apus has a breeding range extending from the western Palearctic, east to Lake Baikal. This is much further east than what is normally realised!
If this statement is correct, then the nominate race breeding in eastern Russia, must migrate SSW over the borders of Mongolia/Kazakhstan, through Afghanistan, the Middle East & south into Africa. This race winters from central Africa, eastwards & southwards down to Mozambique & eastern South Africa.
The nominate race is common throughout its known range. In many countries it is expanding its range & numbers greatly, by utilising human habitations. Therefore, huge numbers must overfly the UAE & other Middle Eastern States on both spring & autumn migrations.

A. a. pekinensis has a breeding range from Iran, east to Mongolia and northern China. Jesper Hornslov (pers comm) is a long time resident in China, he states that he has never seen the nominate race in China. Certainly, he believes that all the Common Swifts I photographed in China were pekinensis. I agree with his opinion.
This race also migrates south west into Africa. The center of its winter distribution being south west south Africa, Namibia & Botswana. To get there, considerble numbers must fly over the Middle East on their migrations.

Pallid Swift

Pallid Swift currently has three recognised races (which has not always been the case):

Apus pallidus brehmorum; A. p. illyricus and A. p. pallidus.

A. p. brehmorum is found from Portugal east to Turkey & along the North African coast. The known wintering range encompasses the Sahel.

A. p. illyricus breeding range is in countries bordering the Adriatic Sea. It winters in the Sahel.

A. p. pallidus has a more southerly breeding range, from the western Sahara, through the Middle East to coastal Pakistan. There is localised wintering in the Middle East and coastal western Pakistan. However, it is thought that most birds, winter in the Sahel.

The Swift situation in the UAE.

The UAE is a small country, and what I have to say here, may come as a surprise to many readers. There appears to be two distinct populations of Pallid Swift here:
 In the northern Emirates, including Dubai, Pallid Swift is a resident breeding bird. They breed in colonies, (which are sometimes large) on cliff faces in the mountains, which is their natural home. However, it is also a common breeding bird on tall buildings within cities, such as Dubai & Sharjah. The number of breeding pairs must be in the order of 5-10,000, although I know of no actual census that has been undertaken.
In Abu Dhabi Emirate, which is approximately 60% of the entire country, this species is a winter breeding bird. Arriving in October/November and departing in early June. This appears to be true in both the Hajar Mountains around Al Ain and much further west in breeding colonies such as the one on Jebel Dhanna. There are reasonable numbers breeding on tall buildings in Abu Dhabi City, such as the ADNOC complex of buildings along the corniche. This species also breeds on offshore islands, which have cliffs and interior mountains and smaller numbers also breed on low-lying cliffs along the western coastline. Sometimes these cliffs are only 15-20 m high, but provide enough cracks & crannies for a colony to survive here. All of these colonies are seasonal breeders and completely absent in the hot summer months.
It would appear that we have two distinct populations here. I find this to be rather surprising, as the areas concerned are only around 160 kms apart at their closest points. This is a very small distance to have two distinct populations, but records show, this appears to be the case.

The Common Swift is a spring and autumn passage migrant in varying numbers, although these numbers are usually small. If one looks at a map of Africa, Europe and Asia one sees that this species should be a much commoner migrant than it actually is. The scarcity of records could be because of the great height at which this species migrates, often only coming lower, (where it may be seen), under certain weather conditions, like thunderstorms, which are rare here in the UAE. Intriguingly, I have also a handful of winter records of this species. Now this is crazy! This species should be nowhere near the UAE in winter. The readers first conclusion would be that I am mistaken in my identification and that the birds in question, are actually Pallid Swifts which just look dark, in certain changing lights. However, I am absolutely convinced that I am correct in my identification.
The Swift situation in the Middle East
Pallid Swift is a common winter breeder to the mountains of northern Oman; most records being from December to April. Slightly further north, it appears to be a summer breeding migrant in places like coastal & mountainous Iran. With a small number being resident.
Common Swift is a fairly common passage migrant in Oman, with records in every month! The peak is spring passage, from February to April. I find the records in every month to be unbelievable! It is a passage migrant through Iran.
I have no doubt at all, that confusion between these two species exists in the Middle East, which clouds the true pattern of occurrence.
How to identify Common and Pallid Swifts?
Basically, in some circumstances it is very difficult and maybe even impossible, without obtaining specimens. However, in most circumstances, providing care is taken, it is quite possible.
Common Swift is a large, rakish swift. The wings are long & scythe-shaped. Wing tips quite pointed. Body is somewhat less torpedo-like, than Pallid Swift, with a narrow vent/rump area, a longish tail with a deep fork.
Common Swift taken in the UK.

Pallid Swift is generally fatter & more barrel chested, than the above species. The wing tips are slightly less pointed than in Common Swift, which makes them appear to be less rakish. The vent/rumps area is thicker and the tail fork slightly shallower.
Pallid Swift taken in Spain.
Common Swift of the nominate race, is blackish. The upperparts often appear to be uniform, being just a touch lighter, on the inner wing. The head appears very dark, with a small, restricted (can be difficult to see) white throat. The underparts in perfect light, are very slightly scaled, but in many situations, look uniform sooty black. The vent is very dark, only in certain lights, can you see any form of scaling. However, as the season progresses, from spring to autumn, birds exhibit a more worn, brownish appearance.
The problems really arise with the plumage pattern of the more eastern race, pekinensis.

I believe all of the above photographs taken at Koko Nor, China are of the pekinensis race of Common Swift. When you look at the photos collectively, the first thing you notice, is how black the general plumage is. This appears to somewhat contradict, the conventional wisdom & the literature on this subject.
A closer inspection, reveals the large pale forehead and matching white throat patch. The area around the eye looks like a black, isolated socket. Even the black bill can be clearly seen contrasting with the surrounding paleness. The white/pale throat patch is extensive and very distinctive. When was the last time you noticed the colour of the bill of a Common Swift of the nominate race?
The structure of these birds is pure Common Swift ie narrow vent/rump, long deeply forked tail; long rakish pointed wings etc. However, the general plumage is somewhat reminiscent of the African Black Swift ( a species I know very well). There is a very marked contrast on the upperwing between the blacker primaries and the much paler secondaries. You don't see this to this extent on the nominate race (in fact this is one of the features used to identify Common Swift from the African Black Swift). The underwing pattern is very striking indeed! The contrast between the black underwing coverts and the more silvery rest of the underwing is quite extraordinary! Look how extensive the silver/pale area is, right up to the tips of the primaries. Also note, the slightly more greyer tones to the vent area, with distinct pale scaling visible on most photos.

These Swifts photographed, were just a few of several hundred, which appeared to be migrating, even further north than Xingang Province. They were feeding low down , then moving on quickly, being replaced by another wave of birds, minutes later. You could actually see the birds departing north, after feeding around the lake & marshes.
Now, why do I think these birds are of the pekinensis race? Well the first thing is they are very distinct looking from the nominate race and totally different from what I was lead to be believe by reading the literarure. They are much blacker & yet at the same time much more contrasting! They are also much less-like Pallid Swift than I was lead to believe.
These individuals match very closely with my winter records of Common Swift in the UAE. I put in my field notes, how black the birds were, and yet noticeably scaled on the underparts and slightly scaled on the upperparts. I also noted the very contrasting underwing pattern. Having seen these birds in China, I now believe my winter records of Common Swift were infact, pekinensis race. I believe that all of my spring & autumn records of Common Swift were of the nominate race. All of them look exactly like the birds I am familiar with in western Europe and the wintering birds on the highveld in Zimbabwe & South Africa.

1 comment:

  1. Hi Steve. Very interesting post. I have just been photographing pekinensis Common Swifts in Beijing (around Tiananmen Square) this week and will be posting some images and comments on shortly. This post has therefore been very topical. Some of my birds look like your pekinensis from Qinghai but one of the first things I learned is that they are variable! Cheers, Terry