do swallows over winter? - the reply

As promised (albeit a day late), the reply the question I posed back on 26 December - do swallows over-winter in southern Spain? As this question was also put in the Spanish avesforum and in my Spanish blog, there are two replies in particular that I translate here. The first is from my good friend Dr. Ernest García who first proposed this to me several years since and which I was going to quote in any case as I like it and it is feasible. The second is Javier Ortega Pinilla of Madrid which gives his own theory, as does Alfons in a comment in my Spanish blog and which to some extent supports Javier's theory, and the final one from Alejandro Onrubia of the Migres Foundation and complements that of Ernest, so here goes.

Ernest wrote: I have commented reviously in this forum that the possibility of wintering hirundines (apart from the Crag Martin which is a wintering species) can be demonstrated only if birds in moult are found in the Peninsula. These species, like the majority of passerines, underatke a complete after breeding. In the case of the hirundines there are cases of partial moult in Europe which is then suspended until the birds arrive at their wintering areas in Africa. The normal pattern is that the birds fly to Africa and there, where there are highly favourable feeding conditions, moult the plumage. I believe that it is most probable that the swallows and martins which are seen in the the south of Peninsula from the end of December and especially in January are birds which have returned early from Africa having moulted and return to spend some time in the more tolerable areas for them in the Peninsula. They also have the advantage of arriving at their nesting areas before those which stay in Africa until March.

In order to fully over winter in Iberia they would have to complete the moult in mid winter, something which needs much more food than is needed to just survive. The ringers in southern Spain could inform us if they find swallows in active moult in mid winter, or if the birds seen then have fully completed their moult. I would like to know their data if it exists.

Javier wrote (and I quote only the relevant part) : I believe that as autumn extends more and more and some species are able to find food until the winter is on its way, it is easier fpr them to stay and delay the time of departure for Africa. It is clear, or it seems so to me, that the climate change and global warming is affecting the species.

Alfons wrote : .... some swallows have been frequenting, feeding on flies and roosting in a pig farm during all November and until mid December. The swallows slept on the beams where they had their nests and towards mid December they left the farm. Are they retarded migrants? Opportunist semi wintering birds? What have these swallowsdone and where have they gone? Have they moved south or have they stayed in some coastal area where the climate is more benign or have they been trapped by the cold? Perhaos some of these migrants which we see in autumn and early winter are birds which are unable to migrate for some reason such as weakness, illness, lack of adequate nutrition.They move as and when they are able.

And finally from Alex Onrubia:
This is a very interesting theme. As Ernest rightly indicates, it is not easy to distinguish 'wintering' birds from those which have returned early and the moult status is a possible indicator of prioving their status.

Here in the south of the Peninsula we caught (for ringing) some swallows in the Januaries of 2009 and 2010 and not ne was in moult. Nevertheless, we have caught some swallows in northern Morocco in January which were undertaking complete moult.

Wit respect to the moult of swallows, we have caught birds in Sepember in Cádiz in complete active moult, these constituting up to 20% of the birds on some dates, and on at least four occasions birds were moulting the last (outer) primary in September in southern Spain!

I believe that more information is needed from ringing recoveries and other techniques (perhaps isotopes?) in order to ascertain the origin of these 'wintering' birds.

So there you are! Interesting this birding, isn't it?

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