Residing on Gibraltar, I’m, at 36oN, simply north of the Sahara Desert. I usually surprise what the hen distribution can be like right here if there wasn’t a desert. I’d anticipate a gradient from these heat temperate latitudes all the way down to the tropics. It should as soon as have been like that. The desert creates an actual barrier, one which splits hen distributions fairly severely.
However the distinction of trans-Saharan to pre-Saharan migrants is just not that clear-cut. Many species have wintering populations on each side of the desert: Blackcaps (Sylvia atricapilla) and Chiffchaffs (Phylloscopus collybita) amongst others. However there are but others which we think about strict trans-Saharan migrants however which do retain wintering components north of the desert.
The Hoopoe (Upupa epops) is the prime instance for me. These birds attain us in giant numbers from tropical Africa within the early spring however others by no means depart. The numbers of Hoopoes wintering in Morocco and southern Iberia are substantial and I even see them recurrently in winter within the central tablelands of Spain, round Toledo for instance. There may be clearly loads of meals for these birds to not go away for the winter. One other instance is the Wryneck (Jynx torquilla).
I’ve been in a position to doc the altering sample of birds remaining north of the desert over the previous many years. The perfect instance was offered by White Storks (Ciconia ciconia). I can exit any day now and I’ll see White Storks. The change occurred within the late seventies and eighties as many birds remained and survived by dwelling from meals present in open refuse ideas. That was not a climate-driven change however, as a substitute, by human actions.
A variety of different species are common in winter nevertheless it isn’t at all times clear if they’re wintering or returning as quickly as circumstances enhance. See my first submit, of 14th July. These birds could be wintering in small numbers and, if they’re able to survive, may have the benefit of being near the breeding grounds and of not having needed to cross the desert. Amongst these species are Booted Eagle (Hieraaetus pennatus), Swallow (Hirundo rustica), Crimson-rumped Swallow (Cecropis daurica) and Home Martin (Delichon urbicum).
Others are a bit extra excessive. There are occasional sightings of Quick-toed Snake Eagles (Circaetus gallicus) within the winter however, within the absence of energetic snakes, we’ve got to surprise what number of of those survive in any respect. Maybe essentially the most uncommon of all is the Pallid Swift (Apus pallidus). This hen is a summer time customer however a couple of years in the past a big winter roost was reported in a constructing within the metropolis of Seville. If daytime temperatures have been excessive sufficient, there isn’t any purpose why these birds couldn’t have survived within the decrease Guadalquivir Valley. It goes to indicate simply how versatile birds are and the way fast populations are in a position to answer adjustments in environmental circumstances. In edge areas like mine, I can’t however assist feeling that I’m dwelling a pure experiment that’s occurring in entrance of my eyes.
