Thursday, 14 March 2013

Session 8 - 14th March 2013

We began the session with a recap on the birds seen during our full day fieldtrip to Fairburn Ings RSPB last week, and a total of 57 species were agreed by the class as a whole.  Then Peter asked us to consider which places we would like to go to on our seven half day fieldtrips which make up next term.  A sheet was also given out for us to complete regarding topics we would like to cover in the next academic year.

The main focus of this session was on the second part of Bird Migration - the amazing statistics.  Migration is one of the most astonishing feats of the natural world with millions of birds migrating over long distances in order to benefit from seasonal resource surpluses and to avoid predators and competitors.

The scale of bird migration is difficult to comprehend - here is a rough estimate of the European population of common migratory species returning to Africa with their newly fledged juveniles each Autumn:

 Migrating Bird  Number (in millions) 
 Willow Warbler
 Sand Martin
 Tree Pipit
 Spotted Flycatcher
 Garden Warbler
 Lesser Whitethroat 
 Ortolan Bunting
 House Martin
 Yellow Wagtail
Pied Flycatcher

The above 16 species alone account for 3,300 million migrants going into Africa. On top of this another 50 species of songbirds go into Africa in varying numbers as well as about 40 million birds of prey, which are mainly falcons but with up to 1 million being Steppe Buzzards (Eastern Race). About 700,000 White Storks also leave Europe for Africa and small passerines including a huge number of Swifts also account for another 200 million birds.  In total therefore, around 500 million birds migrate to Africa each year and this excludes waders, sea birds and water birds.  This means that on average one bird from every five acres of Europe migrates there - phew!

The birds migrate on a broad front across 2,500 miles from Portugal to Eastern Turkey. 500 million migrants means 2 million birds per mile of coastline each autumn.  The main migration event lasts six weeks and that mean 50,000 birds cross each mile of coastline each night.

We finished off this topic by looking at the migratory habits of some individual species including Robin, Chaffinch, Blackbird as well as what triggers migration and which time of day each species migrates.  We also briefly considered the migration routes for different types of birds, with large birds such a Cranes and some birds of prey not being able to sustain flapping flight choosing the path with the shortest area of water to cross, such as at Gibraltar or the east end of the Mediterranean Sea.

With spring nearly upon us, we next looked at the Raptors which are summer visitors (March to October) to Britain. In addition to the twelve winter Raptors discussed in a previous session, a further four are summer only visitors, with only the Marsh Harrier being either resident or migratory.  The four 'extra' birds are:
The best way to identify these summer Raptors is to familiarise ourselves with our common residents, so that differences can be identified.  The way a Buzzard or Harrier flies should be known as well as how the three resident falcons behave. It is only when the common birds can be confidently identified that the scarcer birds which are not seen all year round can be spotted.

The ability to differentiate between flying Buzzards and Harriers is vital and once this is learnt, we need to know which features separate our Common Buzzard from the Honey-buzzard in flight, and know how they hold their wings when soaring or gliding. The Honey Buzzard holds its wings very flat and it has a longer tail whereas the Common Buzzard's wings are held in a much deeper V shape and its tail length doesn't exceed its wing width.  The Honey Buzzard generally has three unevenly spaced dark bands underneath with a broad terminal band.

The Peregrine and Merlin are two falcons which chase birds and so they have broad based wings for power and fast flapping flight. The Kestrel however is a falcon which doesn't chase birds, preferring to eats voles and small rodents and so it drops on its prey from a height.  Its narrower pointed wings are built for hovering and its tail length is much longer as it is used for stability in the air.  The Hobby which eats both dragonflies and sometimes small birds also has narrow pointed wings.

We went on to look at Wykeham Forest which is a site in Yorkshire 10 miles east of Pickering on the road to Scarborough which is famed for its views of Goshawks and, from May to August, Honey Buzzards.  A map was given out as well as directions to the Forestry Commission's Raptor Viewpoint overlooking the keepered woods to the north of the viewpoint.  Goshawks can be seen all year round above the breeding wood but are best seen on calm sunny days from February to late April when they engage in their 'skydancing' breeding behaviour.

Summarise Yorkshire Post article on Goshawks and Honey Buzzards here ...

Our Bird in Focus this week was the Yellowhammer which was once a very common bird in Britain but which sadly is now in decline. We read through another article from Yorkshire Post ....

Male Kingfisher at Moore Nature Reserve - (c) Martyn Jones

Martyn then did his usual 'show and tell', with closeup photos of a male Kingfisher as well as female Reed Bunting that he just wanted confirming.  He also had some record shots of the hard to find female Lesser Spotted Woodpecker from Moore Nature Reserve in Warrington.

Finally some map and direction sheets were given out for Dunsop Bridge and Pendle Hill in Lancashire for those members of the class who wanted to go to look for Goshawks and Dotterel in these two places respectively.

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