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Thread subject: More Migration thoughts.
||09/06/05 08:53 pm
||It says in my Birder's Handbook that preparation for MIGRATION involves both physiological and behavioral changes. Physiological preparation includes putting on FAT to provide FUEL for their long and arduous migration. Smaller birds can lose up to half their body weight when flying over water for long periods of time. those birds that fly at night, passerines( song birds) tend to change their behaviour by altering their activity rhythms during darkness and begin to orient themselves in the direction they will be flying. Swallows and swifts apparently fly non stop and feed on the wing as they fly. Small birds nearly all fly at night using the stars as a compass.
In many bird species, males winter further north than females or juveniles, however where the female is LARGER than the male as in raptors and owls, the female may winter farther north than the males. Three arguments have been put forth for these findings.
!) The body size of females make them better at tolerating inclement weather farther North so that is why they may stay closer to their breeding places. So smaller birds and inexperienced fledglings may tend to migrate to areas farther south.
2) Dominance within a pair relationship may dictate that the more subordinate individual fly farther south.
3) The swift arrival time back at the breeding grounds may influence who winters farther north especially when fierce competition is a factor for securing a nest site, between members of the same sex. If these birds have less distance to travel by staying north of their partners chosen territory then this arrangement may provide the best possible breeding success following migration back north.
Keep tuned.............more to come each day on migration.
||09/07/05 05:23 am
||Looking forward to Migration 101!
||09/07/05 08:20 am
||Thank you for this wonderful information. The more we know about migrating birds, the more we enjoy and appreciate them.
||09/07/05 12:23 pm
||Migration is a subject that absolutely fascinates me. Apart from the physical effort, how on earth do the birds know where to go, and how do they manage to come back to the same neighbourhood in the Spring?
Does your book say anything about metabolism of extra fat? I have heard somewhere that a by-product of all the fat burned on migration is water and that is why the birds can cross deserts without a drink. If the bird hasent got enough fat to complete its journey it starts burning up other tissue and then often dies on arrival.
There is a group of islands off the SW coast of England called The Scillies, and twitchers flock there in October to add all the American birds that have got blown across the Atlantic to their year lists. I will not go because I believe most of the poor birds are in a terrible state, some cant walk because their leg muscles have gone, or they cant eat. Most of them die soon after arriving. I would find that very upsetting.
On the other hand I have been to the Straights of Gibralter in September to see all the birds migrating across the straits to Africa. The small birds just go but the raptors wait for the thermals, climb up on them and then virtually glide the 20 miles across. They have to be careful that the wind is not blowing from the east because they could get blown out into the Atlantic. And sometimes they turn back if they are not happy. But on a good day you can see 1000 raptors going across as far as the eye can see. And flocks of up to 3000 storks. A spectacle you never forget.
||09/07/05 12:35 pm
||smile............Anne I will check for you later. Off to physio now.......