Dwelling on Gibraltar, I’m, at 36oN, simply north of the Sahara Desert. I typically marvel what the hen distribution can be like right here if there wasn’t a desert. I might count on 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 just isn’t 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 take into account 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 massive 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 frequently in winter within the central tablelands of Spain, round Toledo for instance. There’s 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 a long time. 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 all the time clear if they’re wintering or returning as quickly as situations enhance. See my first submit, of 14th July. These birds could be wintering in small numbers and, if they can survive, can 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), Pink-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 now have to marvel 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 season customer however a number 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 is no such thing as a motive 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 modifications in environmental situations. In edge places like mine, I can’t however assist feeling that I’m dwelling a pure experiment that’s taking place in entrance of my eyes.
