Separating the wheat from the (chiff)chaff

The Chiffchaff superspecies complex is a menagerie of numerous species and subspecies. Two subspecies of the Common Chiffchaff (Phylloscopus collybita) – the ‘Siberian’ Chiffchaff (P.c. tristis) and the ‘European’ Chiffchaff (P.c. abietinus) – meet in a hybrid zone that runs alongside the Ural Mountains. Outside this hybrid zone both subspecies are clearly different, but inside the zone intermediates reign supreme.

The hybrid zone between Siberian and European Chiffchaff was already described in 1879 by Suskhin in his report about “Birds of the Ufa province” in the Proceedings of the knowledge about the flora and fauna of the Russian Empire. The zone is characterized by substantial variation in body size, plumage coloration and song types (Marova et al. 2009). This lush morphological and acoustic diversity has prompted some to propose a third subspecies in this region: P.c. fulvescens (Dean & Svensson 2005).

Now, Shipilina et al. (2017) revisit this hybrid zone, combining genetic, phenotypic and acoustic data. They show that the subspecies are clearly differentiated in allopatry (i.e. outside the hybrid zone). Where they co-occur, however, there are many intermediate phenotypic characters as well as mixed singers, interweaving notes from abietinus and tristis songs.  The genetic analyses, based on mtDNA and whole-genome sequence data, indicates high levels of gene exchange between the subspecies. All in all, your typical avian hybrid zone.

The analysis of this hybrid zone also shows that the putative third subspecies (P.c. fulvescens) does probably not exist. It is merely a mirage in a desert of hybridization.


Common Chiffchaff (left) and Siberian Chiffchaff. Picture by Vincent van der Spek (



Dean, A. R. & Svensson, L. (2005). Siberian Chiffchaff’revisited. British Birds 98, 396.

Marova, I., Fedorov, V., Shipilina, D. & Alekseev, V. (2009). Genetic and vocal differentiation in hybrid zones of passerine birds: Siberian and European chiffchaffs (Phylloscopus [collybita] tristis and Ph.[c.] abietinus) in the southern Urals. In Doklady Biological Sciences, vol. 427, pp. 384-386. Springer.

Shipilina, D., Serbyn, M., Ivanitskii, V., Marova, I. & Backström, N. (2017). Patterns of genetic, phenotypic, and acoustic variation across a chiffchaff (Phylloscopus collybita abietinus/tristis) hybrid zone. Ecology and Evolution.

Interspecific Spooning

First case of natural hybridization between two spoonbills, documented in South Korea.

Hybrids between different spoonbill species (family Threskiornithidae) have only been observed in captivity. For example, the International Zoo Yearbook of 1984 reports hybrids between a Roseate (Platalea ajaja) and a Eurasian (P. leucorodia) spoonbill and between an African (P. alba) and a Eurasian spoonbill.

In a recent paper in the journal Waterbirds, Korean researchers describe the first natural hybridization event between different spoonbill species. On a small breeding island in Incheon, a male Eurasian spoonbill paired up with two female Black-faced spoonbills (P. minor) during different breeding seasons (2012-2013 and 2014-2015). In total, eleven eggs were laid, producing nine healthy hybrids.



Male Eurasian spoonbill on the nest, visited by his female companion, a Black-faced spoonbill. Picture taken in Gaksiam, Incheon, South Korea (from: Kwon et al. 2017).



Kwon, I.-K., Lee, K.-S., Lee, J.-Y., Park, J.-H. & Yoo, J.-C. (2017). Hybridization between the Black-Faced Spoonbill (Platalea minor) and Eurasian Spoonbill (Platalea leucorodia) in South Korea. Waterbirds 40, 77-81.

It’s not a new species, it’s a hybrid!

In 1951 American ornithologist Rodolphe Meyer de Schauensee did what many dream of: he described a new bird species: the Argus Bare-eye (Phlegopsis barringeri). This new species of antbird was based on one specimen, collected on the Rio Rumiyaco in Colombia.

Later, Willis (1979) suggested that the specimen might be a hybrid between Black-spotted Bare-eye (P. nigromaculata) and Red-winged Bare-eye (P. erythroptera). These two species overlap from eastern Colombia to northern Bolivia.

This suggestion was tested by Graves (1992), who reexamined the original specimen and compared it to the two putative parental species. His conclusion: it’s a hybrid!


Black-spotted Bare-eye (from Wikimedia Commons)


Graves, G. (1992). Diagnosis of a hybrid antbird (Phlegopsis nigromaculata× Phlegopsis erythroptera) and the rarity of hybridization among suboscines. Proceedings of the Biological Society of Washington 105, 838-840.

Willis, E. O. (1979). Comportamento e ecologia da maede-taoca, Phlegopsis nigromaculata (d’Orbigny & Lafresnaye)(Aves, Formicariidae). Rev. Brasil Biol 39, 117-159.

These papers have been added to the Thamnophilidae page. A special thank you to Mort Isler for directing me to this case.

Conservation of the Mottled Duck: Multiple Populations and a Feral Threat

The Mottled duck (Anas fulvigula) is a North-American dabbling duck species. There are two main populations: one in Florida and one in Louisiana, Texas and Northern Mexico (known as the Western Gulf Coast population). In addition, a third population originated in 1976 and 1982 when about 1200 Western Gulf Coast and 26 Florida ducks were introduced in South Carolina.


A male Mottled duck (picture by Dick Daniels –

Whether the two main populations (Florida and Western Gulf Coast) can be considered discrete populations is unclear. If so, they should be recognized as separate conservation units. Although there is some genetic evidence that these populations are isolated, it remains to be determined if the genetic differences between these populations are simply a consequence of geographic distance (a pattern known as isolation-by-distance or IBD). To settle this issue, Peters et al. (2016) sequenced over 3000 genetic loci for 100 Mottled ducks from the three populations.

The multilocus data clearly separated the two main populations. In addition, kinship coefficients showed a sharp transition that coincides with the range gap between the populations. If these populations were still connected by gene flow, the transition would have been smoother. Finally, modelling of the demographic history of these populations indicated low levels of gene flow (about 1-3 individuals per generation).

These genetic results are backed up by ringing data: Mottled ducks ringed in Florida have never been recovered in Texas or Louisiana (2075 recoveries), and vice versa (8111 recoveries).

The authors conclude that ‘collectively, these results suggest that Florida and Western Gulf Coast Mottled ducks are on independent evolutionary trajectories and may be in the early stages of speciation. Therefore, they should be considered as distinct units for conservation and management.’

Apart from the 100 Mottled ducks, 17 Mallards (Anas platyrhynchos) were included in the analyses. Feral mallards are interbreeding with Mottled ducks and this genetic study confirms high levels of gene flow between these species. Hybridization with the Mallard, in combination with habitat loss, is a major conservation threat for the Mottled duck. Therefore, it is important for managers to confidently discriminate between Mottled ducks, Mallards, and their hybrids. For this purpose, Bielefeld et al. (2016) developed a genetically cross-validated phenotypic key.



Bielefeld, R. R., Engilis, A., Feddersen, J. C., Eadie, J. M., Tringali, M. D. & Benedict, R. J. (2016). Is it a mottled duck? The key is in the feathers. Wildlife Society Bulletin 40, 446-455.

Peters, J. L., Lavretsky, P., DaCosta, J. M., Bielefeld, R. R., Feddersen, J. C. & Sorenson, M. D. (2016). Population genomic data delineate conservation units in mottled ducks (Anas fulvigula). Biological Conservation 203, 272-281.

These two papers have been added to the Anseriformes page.

A New Year and some new papers

The end of 2016 has been quite hectic for me as I successfully defended my PhD thesis (read a report of that day here). So, I took some well-deserved holidays. But at the start of 2017, I felt the urge to update the Avian Hybrids Project. Here is an overview of some recent papers.


(House Sparrow x Spanish Sparrow)^2

In Northern Africa, House Sparrow and Spanish Sparrow also interbreed (Summers‐Smith & Vernon, 1972). In Algeria, House Sparrows and hybrids mainly reside in urban areas, while Spanish Sparrows live in cultivated areas. The latter also breed later and raise only two clutches (House Sparrows and hybrids raise three clutches). The mitogenome of the House Sparrow has almost completed introgressed into the Italian Sparrow (see above). In Algeria, however, a small percentage of the hybrids has a Spanish haplotype (Belkacem et al., 2016).

Belkacem, A. A., Gast, O., Stuckas, H., Canal, D., LoValvo, M., Giacalone, G. & Packert, M. (2016). North African hybrid sparrows (Passer domesticus, P. hispaniolensis) back from oblivion – ecological segregation and asymmetric mitochondrial introgression between parental species. Ecology and Evolution 6, 5190-5206.

Spanish Sparrow in Sardinia (picture by Francesco Canu)


Lord of the Rings

The Short-tailed Albatross (Phoebastria albatrus) is a vulnerable seabird that mainly breeds on Torishima and the Senkaku Islands in the Pacific Ocean. The two populations are genetically distinct and display assortative mating. However, a study based on mate choice of ringed (from Torishima) and unringed birds (from the Senkaku Islands) revealed some mixed pairings, indicating that pre-mating isolation is incomplete (Eda et al., 2016).

Eda, M., Izumi, H., Konno, S., Konno, M. & Sato, F. (2016). Assortative mating in two populations of Short‐tailed Albatross Phoebastria albatrus on Torishima. Ibis 158, 868-875.

Short-tailed Albatross (picture by James Lloyd Pace)


Mangrove Matings

The Mangrove Finch (Camarhynchus heliobates) is critically endangered and currently restricted to one small population on Isabela Island (Galapagos Islands). A genetic study found that a number of individuals have hybridized with the closely related Woodpecker Finch (C. pallidus). Possibly, there is a breakdown of reproductive isolation between these species because the Mangrove Finches cannot find a mate due to the low population size (Lawson et al., 2016).

Lawson, L. P., Fessl, B., Vargas, F. H., Farrington, H. L., Cunninghame, H. F., Mueller, J. C., Nemeth, E., Sevilla, P. C. & Petren, K. (2016). Slow motion extinction: inbreeding, introgression, and loss in the critically endangered mangrove finch (Camarhynchus heliobates). Conservation Genetics, 1-12.

Mangrove Finch (picture by Michael Dvorak)


Lonely Lineages

A genomic analysis of a contact zone between two divergence lineages of the Brown Creeper (Certhia americana) in the Madrean Archipelago sky islands (Arizona, USA) reported complete allopatry during the breeding season and no gene flow (Manthey, Robbins & Moyle, 2016).

Manthey, J. D., Robbins, M. B. & Moyle, R. G. (2016). A genomic investigation of the putative contact zone between divergent Brown Creeper (Certhia americana) lineages: chromosomal patterns of genetic differentiation. Genome 59, 115-25.

Brown Creeper


Keep an eye on the website, more updates will follow soon!

Spring Updates, including artistic Pheasants and Promiscuous Petrels

I finally found the time to update some of the pages on the Avian Hybrids Project. Here is an overview of the most recent papers on avian hybridization.


A nearly 900 year-old drawing of a hybrid Pheasant from China (Peng et al. 2016).

Lavretsky, P., Peters, J. L., Winker, K., Bahn, V., Kulikova, I., Zhuravlev, Y. N., Wilson, R. E., Barger, C., Gurney, K. & McCracken, K. G. (2016). Becoming pure: identifying generational classes of admixed individuals within lesser and greater scaup populations. Molecular Ecology.

Jiménez, R. A. & Ornelas, J. F. (2016). Historical and current introgression in a Mesoamerican hummingbird species complex: a biogeographic perspective. PeerJ 4, e1556.

Tennyson, A., Lawrence, H., Taylot, G. & Imber, M. (2013). A hybrid gadfly petrel suggests that soft-plumaged petrels (Pterodroma mollis) had colonised the Antipodes Islands by the 1920s. Notornis60, 290-295.

Peng, M. S., Wu, F., Murphy, R. W., Yang, X. J. & Zhang, Y. P. (2016). An ancient record of an avian hybrid and the potential uses of art in ecology and conservation. Ibis 158, 444-445.

Sardell, J. M. & Uy, J. A. (2016). Hybridization following recent secondary contact results in asymmetric genotypic and phenotypic introgression between island species of Myzomela honeyeaters. Evolution 70, 257-269.

Walsh, J., Rowe, R. J., Olsen, B. J., Shriver, W. G. & Kovach, A. I. (2016a). Genotype-environment associations support a mosaic hybrid zone between two tidal marsh birds. Ecol Evol 6, 279-94.

Walsh, J., Shriver, W. G., Olsen, B. J. & Kovach, A. I. (2016b). Differential introgression and the maintenance of species boundaries in an advanced generation avian hybrid zone. BMC Evol Biol16, 65.

Wood, E. M., Barker Swarthout, S. E., Hochachka, W. M., Larkin, J. L., Rohrbaugh, R. W., Rosenberg, K. V. & Rodewald, A. D. (2016). Intermediate habitat associations by hybrids may facilitate genetic introgression in a songbird. Journal of Avian Biology.

An Early Christmas Present: Pictures and Papers

Before diving into the well-deserved Christmas Holidays, I have updated several pages. The new papers can be found below. Apart from that, I received some excellent pictures from Steve Byland (be sure to check out his website:

Feel free to send me papers I have missed and pictures of possible hybrids.

Merry Christmas and Happy New Year!

Little Blue - Litte Egret HYBRID - Byland IMG_6105

Presumed hybrid between Little Blue Heron (Egretta caerulea) and Little Egret (E. garzetta)


Added Papers

Campagna, L., Gronau, I., Silveira, L. F., Siepel, A. & Lovette, I. J. (2015). Distinguishing noise from signal in patterns of genomic divergence in a highly polymorphic avian radiation. Molecular Ecology 24, 4238-4251.

Bailey, R. I., Tesaker, M. R., Trier, C. N. & Saetre, G. P. (2015). Strong selection on male plumage in a hybrid zone between a hybrid bird species and one of its parents. Journal of Evolutionary Biology28, 1257-1269.

Greig, E. I., Baldassarre, D. T. & Webster, M. S. (2015). Differential rates of phenotypic introgression are associated with male behavioral responses to multiple signals. Evolution 69, 2602-2612.

Heikkinen, M. E., Ruokonen, M., Alexander, M., Aspi, J., Pyhajarvi, T. & Searle, J. B. (2015). Relationship between wild greylag and European domestic geese based on mitochondrial DNA.Animal Genetics 46, 485-497.

Lavretsky, P., Dacosta, J. M., Hernandez-Banos, B. E., Engilis, A., Sorenson, M. D. & Peters, J. L. (2015a). Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards. Molecular Ecology 24, 5364-5378.

Fuchs, J., Ericson, P. G. P., Bonillo, C., Couloux, A. & Pasquet, E. (2015). The complex phylogeography of the Indo-Malayan Alophoixus bulbuls with the description of a putative new ring species complex. Molecular Ecology 24, 5460-5474.

Pereira, R. J. & Wake, D. B. (2015). Ring species as demonstrations of the continuum of species formation. Molecular Ecology 24, 5312-5314.

Nater, A., Burri, R., Kawakami, T., Smeds, L. & Ellegren, H. (2015). Resolving Evolutionary Relationships in Closely Related Species with Whole-Genome Sequencing Data. Systematic Biology64, 1000-1017.

van de Crommenacker, J., Bourgeois, Y. X. C., Warren, B. H., Jackson, H., Fleischer-Dogley, F., Groombridge, J. & Bunbury, N. (2015). Using molecular tools to guide management of invasive alien species: assessing the genetic impact of a recently introduced island bird population.Diversity and Distributions 21, 1414-1427

Burbidge, T., Parson, T., Caycedo-Rosales, P. C., Cadena, C. D. & Slabbekoorn, H. (2015). Playbacks revisited: asymmetry in behavioural response across an acoustic boundary between two parapatric bird species. Behaviour 152, 1933-1951

Burbidge, T., Parson, T., Caycedo-Rosales, P. C., Cadena, C. D. & Slabbekoorn, H. (2015). Playbacks revisited: asymmetry in behavioural response across an acoustic boundary between two parapatric bird species. Behaviour 152, 1933-1951

Miller, M. J., Lipshutz, S. E., Smith, N. G. & Bermingham, E. (2014b). Genetic and phenotypic characterization of a hybrid zone between polyandrous Northern and Wattled Jacanas in Western Panama. Bmc Evolutionary Biology 14.

Sanchez-Donoso, I., Rodríguez-Teijeiro, J. D., Quintanilla, I., Jiménez-Blasco, I., Sardà-Palomera, F., Nadal, J., Puigcerver, M. & Vilà, C. (2015). Influence of game restocking on the migratory behaviour of the common quail, Coturnix coturnix. Evolutionary Ecology Research 16, 493-504.

Alvarez, S., Salter, J. F., McCormack, J. E. & Milá, B. (2015). Speciation in mountain refugia: phylogeography and demographic history of the pine siskin and black‐capped siskin complex.Journal of Avian Biology.

Anich, N. M. (2012). The First Report of Sutton’s Warbler (Northern Parula × Yellow-throated Warbler) in Wisconsin. The Passenger Pigeon 74, 149-155.

Anich, N. M. (2013). An Apparent Dunlin × White-rumped Sandpiper Hybrid at Chequamegon Bay, Wisconsin. The Passenger Pigeon 75, 137-146


Amazonian Hybrids

Recently, Jason T. Weir (University of Toronto Scarborough) and colleagues published a paper on the role of rivers in the origin of Amazonian bird species. In this paper, they also present genetic evidence (based on thousands of SNPs) for hybridization between seven bird species pairs at Amazonian headwaters. The hybridizing species belong to three different passerine families: Furnariidae (Ovenbirds), Pipridae (Manakins) and Thamnophilidae (Antbirds). Consequently, these pages have been updated!

Snow-capped Manakin (Lepidothrix nattereri)


Weir, J. T., Faccio, M. S., Pulido-Santacruz, P., Barrera-Guzman, A. O. & Aleixo, A. (2015). Hybridization in headwater regions, and the role of rivers as drivers of speciation in Amazonian birds. Evolution 69, 1823-1834.

Recent Updates: Flycatchers, Birds-of-Paradise, Eagles and Malagasy Passerines

The following papers have been added to the bird order summaries for the respective orders/families. Enjoy the reading!

Muscicapidae Ficedula

Laaksonen, T., Sirkia, P. M., Calhim, S., Brommer, J. E., Leskinen, P. K., Primmer, C. R., Adamik, P., Artemyev, A. V., Belskii, E., Both, C., Bures, S., Burgess, M. D., Doligez, B., Forsman, J. T., Grinkov, V., Hoffmann, U., Ivankina, E., Kral, M., Krams, I., Lampe, H. M., Moreno, J., Magi, M., Nord, A., Potti, J., Ravussin, P. A. & Sokolov, L. (2015). Sympatric divergence and clinal variation in multiple coloration traits of Ficedula flycatchers. Journal of Evolutionary Biology 28, 779-790. DOI: 10.1111/jeb.12604

Collared Flycatcher (Ficedula albicollis) in Poland. © Frank Vassen

Bernieridae Xanthomixis

Block, N. L., Goodman, S. M., Hackett, S. J., Bates, J. M. & Raherilalao, M. J. (2015). Potential merger of ancient lineages in a passerine bird discovered based on evidence from host-specific ectoparasites. Ecology and Evolution 5, 3743-3755.

Short-billed Tetraka (Xanthomixis zosterops) on the nest


Martin, P. R. (2015). The paradox of the Birds-of-Paradise: persistent hybridization as a signature of historical reinforcement. Ideas in Ecology and Evolution 8.


Lesser Bird-of-Paradise (Paradisaea minor) © Reza Patrama

Accipitriformes – Aquila

Maciorowski, G., Mirski, P. & Vali, U. (2015). Hybridisation dynamics between the Greater Spotted Eagles Aquila clanga and Lesser Spotted Eagles Aquila pomarina in the Biebrza River Valley (NE Poland). Acta Ornithologica 50, 33-41.

Greater spotted eagle in flight.jpg

Greater Spotted Eagle (Aquila clanga) © Вых Пыхманн

Morphology Insufficient to Detect Hybrid Sparrows

Identification of hybrids based on morphological characteristics can be extremely difficult. Hybrids may express a mosaic of parental traits or display extreme phenotypes compared to parental forms (a phenomenon known as transgressive segregation). In addition, extensive backcrossing can result in a continuous gradient of phenotypes across a hybrid zone.

Jennifer Walsh (University of New Hampshire) and colleagues took a closer look at the hybrid zone between Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson’s Sparrow (A. nelsoni). Based on genetic markers, they were able to identify eight recent hybrids, 44 backcrosses to Nelson’s Sparrow and 98 backcrosses to Saltmarsh Sparrow. However, using the morphological variation across the hybrid zone they could only distinguish between Nelson’s and Saltmarsh groups; backcrosses were indistinguishable from the pure parental species. These results indicate that hybrid identification without genetic data will likely lead to a substantial overestimation of the proportion of genetically pure individuals in a population. Hybrid zone research should be a combination of genetic and morphological approaches.

More information on hybridization in the genus Ammodramus and the family Emberizidae can be found here.

A Nelson's Sparrow (or is it a backcross?)

A Nelson’s Sparrow (or is it a backcross?)


Walsh, J., Shriver, W. G., Olsen, B. J., O’Brien, K. M. & Kovach, A. I. (2015). Relationship of phenotypic variation and genetic admixture in the Saltmarsh-Nelson’s sparrow hybrid zone. The Auk 132, 704-716.