Tuesday, 14 February 2012
Willow Tit
Scientific Name:
Poecile montanus
Length:
12 cm
Wingspan (mm):
17-18 cm
Weight:
9-11 g
Lifespan:
Up to 10 years, commonly 1-5. Description
The Willow Tit and Marsh tit are very difficult to tell apart, and were not separated in Britain until 1897.
Most field guides mention cap glossiness, scruffiness, 'bull-neck', bib shape and a pale wing panel as methods of separating Willow from Marsh Tits, but a review of identification criteria in 2009 found only the latter to be in any way useful. Instead, the most reliable features recommended for use were the bill (if seen or photographed well) and cheek pattern. Marsh Tit shows a pale mark at the base of the bill, while Willow has an all-dark black bill - this is 98% reliable, see this paper for illustration and explanation: http://blx1.bto.org/pdf/ringmigration/24_2/broughton1.pdf
Marsh Tits show a contrasting two-tone appearacne to the cheek patch, with a white ear covert and cold-rey brown neck sides. Willow Tits, meanwhile, show a uniformly whitish or pale cream cheek patch, but often with a warm golden buff tinge on the neck forming a subtle collar. Marsh never shows warm buff on the cheek/neck.
A pane panel on the secondaries of the wing is only moderately reliable, as some Marsh can show this and some Willow wont. Underpart colour is not useful, and both species can appear bull-necked or small-headed due to posture or fluffing-up.
Distribution
Formerly widespread, now extinct or rare in many areas while remaining locally frequent in several strongholds.
Largely absent south of a line from Lincoln to the Severn, although isolated populations remain in e.g. West Berks. Extinct in Cambs, Beds, Herts, south Lincs and Kent at least. Virtually extinct in Scotland and does not occur in Ireland. Main strongholds are the West Midlands, Notts, South and West Yorks and Northumbs.
Habitat
Scrub and woodlands. Now rare on farmland, and prefers wet scrub and young woodland (less than 50 years old) where other tit species are scarce - they are submissive to all but the Coal Tit. Like brownfield sites such as abandoned overgrown quarries and industrial sites.
Diet
As Marsh Tit: insects and seeds. Caches food in summer-winter.
Behaviour
Similar to Marsh Tit. Has large territories, up to 10 ha, meaning a low population density. Remains in/around territory throughout the year, and dispersal distances are short. Will visit gardens and bird feeders where they are near a territory, and is fond of sunflower seeds.
Reproduction
Breeds in April-May, having one brood per year. Excavates a nest hole in rotten wood, such as dead birch, willow or elder trunks/branches as little as 10 cm wide. Nets hole is neat and round, approx 27 mm in diameter, located from gruond level to 6 m high. Young fledge in June and disperse quickly, as per Marsh Tit.
Population
Catastrophic decline over the past 40 years, down by c.85%. Reasons for the decline are not known, but potential factors are habitat maturity (they prefer the young stages of woodland and scrub, and lose out to other tits as it matures into woodland), habitat fragmentation, compounded by competition from Blue Tits, predation by Sparrowhawks and Great Spotted Woodpeckers.
Status
Catastrophic decline, extinct or nearly so across large areas. Frequent only in regional strongholds, but still declining nationally.
Did You Know?
While Willow Tits are common across Eurasia, especially in the boreal forest zone, the British Willow Tit is a unique island race that occurs nowhere else in the World.