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1928 Views 6 Replies Last post: May 17, 2011 4:45 PM by Drosophila RSS
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Apr 7, 2011 7:27 PM

Swans, question about migration

The local hospital grounds have their own resident swans.  Last year they hatched six eggs and reared four young.  I was surprised to see the adults and at least two of the cygnets (now as big as their parents) still around in the depth of winter (January I think); apparently not having migrated.  I expect this was because they got well fed by hospital staff and visitors - so why bother?

 

Is this common among swans and other migrants in a similar situation?

  • Currently Being Moderated
    Apr 7, 2011 8:45 PM (in response to Drosophila)
    Re: Swans, question about migration

    Hello,

    You've got it right. Birds won't migrate if they don't need to. If the conditions are bad, they go South, but only as far as they need. But if they find unfrozen lakes with sufficient food and safe places to rest, they will stop there. In the age of feeding wild birds, many migratory species have populations that become resident, at least in towns, and also expand their range North.

    Mute Swans and other birds have northern populations that are summer visitors to their breeding grounds, but southern populations are resident. Even birds that we think of as strictly migratory, such as the Barn Swallow, have resident populations in areas that can sustain them year round, as seen on this map.

    In Britain, as you can see on this RSPB fact file, Mute Swans are resident birds, even though individual birds or families may wander away from the nesting sites.

    Regards,

    Florin

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      • Currently Being Moderated
        Apr 8, 2011 11:49 AM (in response to Drosophila)
        Re: Swans, question about migration

        Hello again,

         

        Starlings are not strictly insectivorous. They can eat berries, soft fruits, seeds, or bread in towns. That’s how they survive long, harsh winters in towns like Montreal. So these species that can switch diets with seasons, are able to live as residents. Tits do the same thing, you know they eat sunflower seeds at bird tables. But they also search the trees for hibernating insects, usually eggs and nymphs hidden on branches and trunks. We humans are able to count the eggs and make an estimate of next summer’s level of infestation with some insects seen as forest pests. But so do the tits! The ones that feed on many insects during winter will lay more eggs in spring, so many chicks will be fed on an abundance of larvae, as predicted by the abundance of eggs.

         

        Swallows are resident in warm, wet areas, where insects are abundant all year round. Why would they leave then?

         

        Adult Swans and other resident birds will chase away their progeny when ready to live independently. They will not tolerate competition for resources, and the young are going elsewhere. That’s not migration, but dispersal.

         

        Regards,

        Florin

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          • Currently Being Moderated
            May 17, 2011 2:45 PM (in response to Drosophila)
            Re: Swans, question about migration

            Hello,

            Sorry about getting back so late.

            I meant to say  that Barn Swallows (Hirundo rustica) are summer visitors on most of  their breeding grounds in the temperate region, including Montreal and  London. But the populations breeding in warm areas such as Egypt are  resident birds there; they don't need to fly away in winter, because  they can find food all year round. The same thing with the Red-rumped  Swallow (Cecropis daurica), who visits Southern Europe during the  summer, but is a resident bird in India and Africa. In those places, in  winter, you will find both the local birds and the northern populations,  living together for a few months.

            There are also many species of  swallows that never migrate, such as the Congo Martin (Riparia congica)  and the White-bibbed Swallow (Hirundo nigrita), both from insect-rich  areas of Africa. I had these species and those Egyptian populations of  the Barn Swallow in my mind when I was asking "why would they migrate?"

            It's  the same in North America. I lived in Montreal for almost four years.  The Barn Swallows there have a red belly instead of white, but they are  the same species.

            In general, the areas where the birds nest is  considered their home land. Of course, penguins and other sea birds are  at home in the high sea, and go on land only briefly, to nest. But Honey  Buzzards come here in Britain every summer for a few years until they  mature, before even establishing a territory and nesting. So I would say  that they are truly at home in Britain and are migrating to Africa to  spend their winter, and not at home in Africa and rushing to Britain  only to breed.

            All the best,

            Florin

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