Some observations on adult Mediterranean Flycatchers on Corsica

Following DNA and morphological studies of Spotted Flycatchers on Corsica, Sardinia and the Balearic Islands published in 2015 (see footnotes for references) the International Ornithological Congress (IOC) split the species into Spotted Flycatcher and Mediterranean Flycatcher with the latter including the nominate Muscicapa tyrrhenica tyrrhenica and the Balearic Island subspecies M t balearica. In January 2018 the BOU adopted the IOC World List for taxonomic purposes and therefore the Mediterranean Flycatcher is a potential addition to the British list. 

This has not been universally accepted and some authorities still treat tyrrhenica and balearica as a race of striata, including the just published Handbook of Western Palearctic Birds by Shirihai & Svensson.

Whatever the ins and outs I'm interested in geographical variation and so a trip to Corsica in July was an opportunity to have a look at the flycatcher for myself. 
The Mediterranean Flycatcher is common on the island and I saw them in the mountain villages to at least 1000m and down to sea level. On the coast the breeding density was particularly high and I had 3 pairs in a 400m strip of pines close to where I was staying.

Generally Mediterranean Flycatcher appears a warmer brown without the grey tones of striata and the breast has less distinct dark streaks and appears more blotchy. In some lights the upper breast can appear almost unstreaked. The effect of the light was very significant, birds looking much browner and less streaked in the strong Mediterranean sun and greyer and more streaked in shadow.

Photo 1 Mediterranean Flycatcher - left in sun, right in shade

Both the above photos are of the same bird taken straight from the camera without any adjustment, other than a little sharpening. Post processing adjustment particularly to the highlights have a big impact on how distinct the streaking appears and on the plumage tones.

Photo 2 Mediterranean Flycatcher as above with post processing adjustments

So the lighting conditions are important when assessing colour and the extent of breast streaking, as is the photo post processing when looking at images.

Photo 3 Mediterranean Flycatcher (left) v Spotted Flycatcher (right)

Photo 3 shows the extent and strength of the breast streaking on the two species. Note how brown the Spotted looks in the sunlight compared to Mediterranean in the shade. The bill looks slightly thicker on Spotted, having a slightly more swollen appearance?
There may be slight differences in the streaking of the crown and nape but I couldn't see anything consistent.

Perhaps the most significant quoted difference between the two species is primary length with Spotted generally having the primary extension greater than the exposed tertials whilst in Mediterranean the primary extension is less than the exposed tertials. This is very difficult to assess in the field and is best done from photographs but they are very dependent on the angle and stance of the bird and also on the condition of the feathers.

Photos 4 & 5; Mediterranean Flycatcher estimation of primary extension (Note lower bird has very worn longest tertial)

Photo 6; Spotted Flycatcher estimation of primary extension (© Ken Smith)

The paper by Michele Vigano & Andrea Corso gives a range of wing measurements and demonstrates that Mediterranean Flycatcher has a shorter wing length, on avarage by 4.6mm,  and more rounded wing. Differences in the primary spacing on the closed wing could therefore be apparent, in the article the most significant difference found was between the longest primary p3 and p2 which unfortunately isn't visible on the closed wing.

Photo 7; Mediterranean (L) v Spotted Flycatcher (R) primary spacing

Apologies if I have the primary numbering incorrect. On the Spotted Flycatcher p3 is longest but this is variable and it doesn't look to me as if there is any obvious difference which would help in the field.

Photo 8; Mediterranean Flycatcher in a typical view, length of the primaries compared to the undertail coverts doesn't appear to help in separating the species presumably due to posture factors

Both Corso & Vigano have stated on BirdForum that an article on the identification of Mediterranean Flycatcher, or Tyrrhenian Flycatcher as they prefer, is in preparation for Dutch Birding. I no longer subscribe but don't think this has been published yet? Andrea Corso also stated that the 'call is clinching too' on BirdForum but didn't elaborate. The Mediterranean Flycatchers were generally vocal and the call was consistently a high pitched seeep usually ending with a tchak. In the UK I most commonly here the seeep alone but have also heard the seeep - tchak. The birds in Corsica were feeding young which may have influenced their calls. I haven't analysed the calls to see if there is any quantifiable difference in frequency. I made a recording which is available below.

In conclusion I think a Spring flycatcher with warm brown tones to the upper parts and subdued breast markings, comprised of brownish blotches rather than distinct dark streaks would be worthy of closer inspection and a primary projection of less than the exposed tertials would be a strong indication of Mediterranean Flycatcher. 
M t balearica is paler and has a slightly shorter wing length (BWP) than nominate tyrrhenica so the features described above should be slightly more obvious in that race of Mediterranean Flycatcher.
If there is a vocal difference that would be an additional factor and possibly a clincher to quote Andrea Corso. 
All the flycatchers are interesting and worth a close look in any case.

Michele Viganò & Andrea Corso; Morphological differences between two subspecies of Spotted Flycatcher Muscicapa striata (Pallas, 1764) (Passeriformes Muscicapidae). 

Biodiversity Journal, 2015, 6 (1): 271–284

Pons et al ; The role of western Mediterranean islands in the evolutionary diversification of the Spotted Flycatcher (Muscicapa striata), a long-distance migratory passerine species. 
Journal of Avian Biology 47(3) · November 2015