*See postscript below for comments/feedback on this post including the uncertainties regarding the 'white-backed' Pied Wheatears of Cape Kaliakra.
Cape Kaliakra is famous for it's breeding population of Pied Wheatears. In previous years there have been regular reports of presumed hybrid Pied x Eastern Black-eared Wheatears (see ebird etc) and indeed this Spring several hybrid birds were present (at least three males).
This post looks at some of the birds present in Spring 2021 (and also some birds from a previous autumn trip in 2019) and also compares a few songs and calls between presumed Pied Wheatears and hybrid Pied x Eastern Black-eared Wheatear.
Spring Wheatears are arguably at their most striking and distinctive following the tips to the autumn/winter feathers wearing away to reveal the characteristic summer plumages. These birds provide the best basis for establishing the hybrid contingent within the local breeding population. Both presumed pure Pied and hybrids were holding territory and presumed to be breeding in the area. At least one male Pied Wheatear was ringed so the population is presumably under study (any more details would be greatly appreciated).
Adult male Pied Wheatear
Adult male Pied Wheatears in Spring are clearly striking birds with jet black mantle and scapulars, wings, face and upper breast with the black on the breast solidly (unbroken) connected to the black upperparts in line with the scapulars. The crown and underparts are a contrasting bright white. In Spring the diagnostic tail pattern (see below) and the lack of white in the primaries in flight exclude Mourning/Maghreb Wheatear and Cyprus Pied Wheatear has generally warmer pale areas and shorter primary projection. Eastern Black-eared Wheatear differ in that the face and breast patch is disconnected from the upperparts. In autumn identification is much more problematic (see below).
The distinctive tail pattern of Pied Wheatear showing the inverted 'T'- shape with black extending up the outer webs of the outer most rectrices - a pattern shared with Black-eared Wheatear
Male Pied Wheatear singing
Calls of several female Pied Wheatear and male singing
First summer-male Pied Wheatear
First-summer male Pied Wheatears show clear moult contrasts and brown worn juvenile feathers in the wings. Typically they have dark markings on the crown.
Female Pied Wheatear
A fairly typical female Pied Wheatear showing dark upperparts extending to upper breast, typical tail pattern and off-white underparts
An unusual female bird showing extensive black on the throat
At the other end of the spectrum was this rather pale looking female Pied Wheatear (perhaps a first-summer?). Considering female Pied and Eastern Black-eared Wheatears are difficult to separate on plumage presumably identifying a hybrid would be extremely challenging.
Adult male hybrid Pied x Eastern Black-eared Wheatear
Adult male Pied x Eastern Black-eared Wheatears (above and below). A striking bird, looking very much like a Finsch's Wheatear (with white mantle and white upperparts that connect with white rump), however the structure is different, the pale tones are too contrasting and critically the tail pattern is Pied-like with black extending up the outer rectrices. Separated mainly from a contrasting Eastern Black-eared Wheatear by black on throat connected to black on upperparts (clearly not connected on Eastern Black-eared).
The tail pattern and extent of white on upperparts shown above and below
A stand off between a male hybrid (left) and male Pied Wheatear (right). The hybrid appears like a first-summer bird with head markings and contrast in the wing feathers.
Songs of male hybrid Pied x Eastern Black-eared Wheatear. The songs of Pied Wheatear and Black-eared Wheatear are very similar and it appears that the song of the hybrids is consistent with the same repertoire. Both hybrids and presumed pure birds used a lot of mimicry in the song with Wood and Green Sandpiper and Yellow Wagtail calls often repeated. I did not record any Eastern Black-eared Wheatears at the Cape this Spring and the only other breeding Wheatear there was Northern Wheatear. The possibility that the hybrids might be Pied x Northern Wheatear should also be considered so I referred the sound recordings to Magnus Robb who commented that he could not hear any Northern Wheatear influence in the hybrid songs/calls and also confirmed that Pied and Eastern Black-eared Wheatear songs were extremely similar also noting that genetically they are also largely undifferentiated. An online search revealed that hybrid Pied x Black-eared Wheatears are regularly recorded in the range overlap zone.
First-summer male hybrid Pied x Black-eared Wheatear
First-summer male hybrid Pied x Eastern Black-eared Wheatears (above) showing the typical first-summer markings on the head and also dark markings on the mantle
This post is mainly focused on Spring birds from 2021 but for comparison here a few photos of autumn birds from Cape Kaliakra taken in 2019 with a few presumed/tentative identifications and comments. The possibility of pure Eastern Black-eared Wheatears on passage must also be considered in these photos (see comments on facebook post below for opinions of some of the identifications which indeed include suggestions of Eastern Black-Eared Wheatear).
Adult male Pied Wheatears, September 2019. The extensive black bases to the mantle and scapulars feathers are clearly visible. The pale tips will wear off to generate the distinctive spring male summer plumages.
A rather Eastern Black-eared Wheatear looking adult bird, September 2019.
This first-winter bird look very Eastern Black-eared Wheatear like. Considering separating first-winter Pieds and Eastern Black-eared Wheatear can be extremely challenging, presumably identifying a hybrid could enter the realms of impossibility.
First-winter male bird
A presumed female Pied Wheatear, typically cold toned with cold fringing to upperparts
Acknowledgements: Thanks to Lee Dingain, Chris Townend and Magnus Robb for feedback/comments.
Handbook of Western Palearctic Birds, Hadarom Shirihai and Lars Svennson
Advanced Bird ID Handbook, The Western Palearctic, Nils Van Duivendijk
Collins Bird Guide
*Postscript: Had some very interesting feedback on this post. Comments in facebook post below and links to research paper and photos of known hybrids from Iran. It is not certain whether the white-backed Pied Wheatears in Eastern Bulgaria/Romania are hybrids or represent a morph, research is on going and more revelations are due to be published in the near future.