SW Spain & Portugal & Separating adult Pallid Swift from Common Swift

I've just returned from a short trip based in El Rompido, near Huelva in South-West Spain. I had no particular target birds but was quite keen to see White-rumped Swift which would be a new bird for me and is not that easy to see in a typical early Spring trip due to its late arrival date.
Rather than do a full write up of the trip I've just focused on some of the more interesting observations starting with Pallid Swift.
Separating adult Pallid Swift from Common Swift
The comments below relate to adults in Spring and compare nominate apus Common Swift with the European brehmorum race of Pallid. I find that the separation of Pallid from Common Swift is not easy unless you have good light and viewing conditions. I have watched groups of swifts at distance against a pale sky when they all tend to look dark and have struggled to decide if they are Pallid and Common Swift. Whilst Common Swifts always look dark Pallid's can too unless they are seen in decent light. 

Pallid (left) with Common Swift

In the coastal villages in SW Spain, in Huelva, El Portil and El Rompido all the swifts seen were Pallid but a little inland at Cartaya there were both Pallid and Common and whilst they appeared to be in separate groups most of the time they were also seen together which allowed direct comparisons to be made.

Pallid Swift (left) and Common Swift

Although the wing length is similar in both species Pallid looks larger with its broader body, outer wing and head giving it a bulkier appearance. On measurements the two out tail feather (T4 & T5) are a similar length in Pallid whereas the outermost tail feather tends to be longest in Common but I've not found this of any use in the field as the relative lengths vary with the extent the tail is spread.

Common Swift (left) and Pallid Swift

Pallid Swift in good light is a pale sandy brown whereas the body of Common Swift in similar light always looks blackish. The underwing of Common Swift can look pale, sometimes silvery, particularly if it is not in shadow there is then significant contrast between the underwing and body which is not seen in Pallid which looks rather uniform from below. From above, and less obviously from below, Pallid shows a darker leading edge to the wing and darker outer primaries which contrast with the paler inner wing where Common looks much more uniform.

Pallid Swifts, the right hand bird has a feather in its bill

How apparent this is depends on the viewing angle and the light.
Pallid has a more extensive pale throat which extends more on to the forehead giving it a very pale faced appearance, particularly when seen head on.

Pallid Swift

The feathers of the body are pale fringed when fresh in both species but this is much more apparent in Pallid giving a much scalier appearance to the breast.
In summary, given decent views in good light, the separation of Pallid from Common Swift should be fairly straight forward but faced with a lone bird in less than ideal viewing conditions detailed notes should be taken to confirm the identification.
White-Rumped and Little Swift
I have been to both Spain and Portugal several times in the early Spring but have generally been too early for White-rumped Swift which tends to arrive in Europe in late May. Visiting SW Spain in mid-June was therefore an ideal time to look for it.

Mertola

I visited both Mertola and Minas de Sao Domingo in Portugal. The former town, around the castle at least, didn't look like particularly good habitat for White-rumped Swift to me although there were plenty of Pallid Swifts. There may be suitable cliff faces along the river or the bridge leading to the town but I didn't explore these but instead moved on to Minas de Sao Domingo which is only about a 20 minute drive back towards the Spanish border.

the old open cast copper mine of Minas de Sao Domingo

The old open cast copper mine has left rock faces that provide nesting habitat for large numbers of House Martins and Red-rumped Swallows whilst the Pallid Swifts appear to prefer the nesting habitat in the nearby town.
Both White-rumped and Little Swifts associate with the House Martin flock in the old mine. There is a boardwalk on two sides of the lake and I was able to get excellent views of both species from here without disturbing the birds. I counted at least 6 White-rumped Swift but only saw 1 Little although there may well have been more. The Little appeared to have a House Martin in close attendance and they came together as if mating on one occasion which was unusual. It took time to get reasonable photos as the light was very harsh, it was also over 35 centigrade in the quarry 

White-Rumped Swift

Little Swift