Identification of Confusion Species #1: Marsh Tit and Willow Tit

Marsh Tit (Poecile palustris) and Willow Tit (Poecile montana), have for many years provided ornithologists and birdwatchers alike with a considerable identification headache. Indeed it was not until 1897 that Willow Tit was first recognised as a distinct species (Holloway, 1996). As was the typical practice of the day, the type specimen was ‘collected.’

Even today, many black-capped tits prove difficult to identify in the field and even for ringers, some individuals showing  intermediate characteristics cannot be safely attributable to species level. The BTO Garden Birdwatch survey still combines the two species due to the constant risk of misidentification and one major field guide even carries a photograph purporting to be one but which is actually of the other.

In the ground-breaking paper Separation of Willow Tit and Marsh Tit in Britain: a review (Broughton, 2009), the author considers that the most reliable separation feature for birds observed in the field is voice.

Here, I will briefly attempt to summarise Broughton’s work.

Voice

Marsh Tit: An explosive ‘pitchou! Willow Tit never gives this call, but beware mimicking Great Tits. Also parts and variations on this call, such as ‘pit-it!’ or ‘chou!’ May also give a ‘dee!’ call, but always preceded by ‘pitchou!’   

Willow Tit: More nasal and buzzing than Marsh Tit, a ‘szi-szi-dzee-dzee!’ or ‘’zi-zi-tah-tah-tah!’ May also give a ‘dee’ call, but never preceded by ‘pitchou!’ 

Bill 

Marsh Tit: Broughton found that 97% of Marsh Tits showed a pale mark on the upper mandible on the bill side by the nostril. Also a pale mark on lower mandible. This is considered the safest physical identification feature, but may be difficult to see in the field.   

Willow Tit: Shows a pale mark on lower mandible, but Broughton found that a pale mark on the upper mandible was lacking in 96% of individuals. 

Cheek pattern

Marsh Tit: Ear coverts are clean and whitish and contrast with grey-brown neck. The colour transition between ear coverts and neck is distinct and abrupt.  

Willow Tit: Cheek is whitish or buff but with no abrupt colour transition behind the ear coverts, instead being subtle gradation. Often appears larger-faced than Marsh Tit.

Wing panel

Marsh Tit: Broughton found that a high percentage (59%) can show a wing panel. Glare can also create the impression of a wing panel.   

Willow Tit: Presence of broad pale fringes to  tertials and secondaries are supportive features of Willow Tit, but are of limited value in isolation.

Cap (extent)

Marsh Tit: Cap extending no further than nape is now considered unreliable with Broughton finding 46% of specimens having cap extending onto mantle.   

Willow Tit: Cap extending onto mantle now considered unrelaiable, with 20% of specimens having cap restricted to nape only.  

Cap (gloss)

Marsh Tit: Glossy black cap now considered an unreliable feature in isolation, with some females having dull caps with brown tones.

Willow Tit: Matt black cap now considered unreliable, with . 28% of Willow Tits showing some cap gloss.  

In summary, some of the features considered diagnostic can no longer be treated as such in isolation. Voice remains the key identification feature, although noting a combination of ‘classic’ bill, cheek pattern, wing panel and cap features for either species would almost certainly lead to reliable identification.

The full paper can be read here

Next week: Slavonian and Black-necked Grebe.

ATB,

DOM

Leave only footprints, kill only time.