Ilkley North West Trail #3: Blackcap - t'Nurfern Nightingale
This is the 3rd of a 13-cache series which takes you on a 4.3km trail around some of the lovely countryside between Middleton and Austby immediately to the northwest of Ilkley above the north bank of the Wharfe. Allowing for an easy pace, stopping for caches | to admire the view | spot birds the trail should take you about 3 hours or so.
See GC8Q381 Ilkley NorthWest Trail #1: Intro & Start for background info on the trail and parking waypoints. See Gallery for a map of the trail showing parking spots and approximate cache locations.
The cache, a small camo-taped tablet pot, is hidden on the trail in the middle of this lovely small patch of broad-leafed woodland. This warbler could be heard singing strongly from high up in one of the nearby mature tree and - once spotted amongst the foliage - quickly identified. This was confirmed by quickly checking on my phone app for UK Birds.
The (Eurasian) blackcap (warbler) (Sylvia atricapilla atricapilla), one of 5 sub-species, is a common and widespread typical warbler. It has mainly olive-grey upperparts and pale grey underparts and both sexes have a distinctive neat coloured cap to the head - black (male) and chestnut (female). They are a similar size to robins - around 13cm long and weighing about 21g.
The male's typical song - a rich musical warbling, often including many bird imitations and ending in a loud high-pitched crescendo given in bursts of up to 30 seconds - has earned it the name 'northern nightingale' (listen here and see/listen here for song & calls with video/photos).
Its closest relative is the garden warbler - similar song but looks quite different. See here for a great compilation video of all the different warblers occurring in UK with their calls which can be very helpful in distinguishing these LBJs in the field..
The species name, like the English name, refers to the male's black cap - atricapilla is from the Latin ater (black) and capillus (hair -of the head).
Although still mostly a summer visitor from Germany and NE Europe, since the 1960s it is increasingly over-wintering in the UK - mainly in England. The UK breeding population is 1,200,000 territories whereas that of winter is some 3,000 birds. Breeding birds arrive April -May and leave September - October.
Its main breeding habitat is mature deciduous woodland, with good scrub cover below the trees. Other 
habitats, such as parks, large gardens and overgrown hedges, are used as long as they meet the essential requirements of tall trees for song posts and an established understory.
Its diet is mostly insects, including flies and caterpillars. But, unlike most warblers, it enjoys berries, especially mistletoe and it is very efficient at spreading mistletoe seeds, eating the flesh of the berry and wiping the seed on a branch, allowing it to potentially germinate there.
Even in mid-winter it will readily come into gardens where it forages for insects and berries and to visit bird feeders and tables where they can be quite feisty competing for access to fruit, fat or seeds (see here).
From ringing it has been known for a while that those coming to UK for winter have mostly been hatched or breed in southern Germany.
Studies of blackcaps in 2 areas of Germany 800km show that those spending winter in Spain had more in common genetically with their Spanish counterparts in the other population than they did with their UK-wintering neighbours which bred in the same area.
This could mean that the Spanish and UK-wintering groups of blackcaps may becoming two different species. The reason for this change in behaviour is that people in the UK put out plenty of bird food making spending the winter here a viable option.
So, if you see a blackcap during winter, make a note of the sighting and report it to one of the wild bird 
organisations which is tracking sightings to learn more about changing behaviour and populations.
Threats: they are caught by Eurasian sparrowhawks in the breeding range, and by Eleonora's falcons on migration. Jays and magpies take eggs and young, as do mammals such as stoats, weasels and squirrels. However, domestic cats are the most important predator, possibly killing up to 10% of the population.
See here for more information on this attractive & melodious bird.