(Feel free to email me for PDFs of articles below that I have co-authored.)

Latest preprints (not yet published in a peer-reviewed journal)

Nikelski, E., A.S. Rubtsov, and D. Irwin. 2023. Evidence for a chromosomal inversion maintaining divergent plumage phenotypes between extensively hybridizing yellowhammers (Emberiza citrinella) and pine buntings (E. leucocephalos). Preprint (not yet peer-reviewed) on bioRxiv:

Natola, L., and D. Irwin. 2023. Evidence for ancient selective sweeps followed by differentiation among three species of Sphyrapicus sapsuckers. Preprint (not yet peer-reviewed) on bioRxiv:

Natola, L., and F. Tousley. 2022. 3D-printed decoys are as effective as taxidermied decoys in attracting red-breasted sapsuckers for mist-netting. Preprint (not yet peer-reviewed) on bioRxiv:


McCallum, Q., K. Askelson, F.F. Fogarty, L. Natola, E. Nikelski, A. Huang, and D. Irwin. 2024. Pronounced differentiation on the Z chromosome and parts of the autosomes in crowned sparrows contrasts with mitochondrial paraphyly: implications for speciation. Journal of Evolutionary Biology, voae004,
(earlier version posted on bioRxiv: Link )


Askelson, K., G.M. Spellman, and D. Irwin. 2023. Genomic divergence and introgression between cryptic species of a widespread North American songbird. Molecular Ecology 32: 6839-6853. Link

Natola, L., S.M. Billerman, M.D. Carling, S.S. Seneviratne, and D. Irwin. 2023. Geographic variability of hybridization between red-breasted and red-naped sapsuckers. Evolution 77: 580-592. Link
(earlier version posted on bioRxiv: Link )

Nikelski, E.*, A.S. Rubtsov, and D. Irwin. 2023. High heterogeneity in genomic differentiation between phenotypically divergent songbirds: a test of mitonuclear co-introgression. Heredity 130: 1-13. Link  *For this paper, Ellen Nikelski received the Best Student Paper 2023 prize from the journal Heredity, the official journal of the Genetics Society.
(earlier version posted on bioRxiv: Link )

Ore, M.J., S. Wang, and D. Irwin. 2023. Gradual transitions in genetics and songs between coastal and inland populations of Setophaga townsendi. Ornithology 140(2:April): 1-14.


de Zwaan, D.R., J. Mackenzie, E. Mikkelsen, C. Wood, and S. Wang. 2022. Pleiotropic opposing dominance within a color gene block contributes to a nascent species boundary via its influence on hybrid male territorial behavior. PNAS Nexus 1: 1-6. Link

Irwin, D., and D. Schluter. 2022. Hybridization and the coexistence of species. American Naturalist 200(3): E93-E109. Link
(earlier version posted on bioRxiv: Link )

Natola, L., S.S. Seneviratne, and D. Irwin. 2022. Population genomics of an emergent tri-species hybrid zone. Molecular Ecology 31: 5356-5367. Link
(earlier version posted on bioRxiv: Link )


Wang, S., M.J. Ore, E.K. Mikkelsen, J. Lee-Yaw, D.P.L. Toews, S. Rohwer, and D. Irwin. 2021. Signatures of mitonuclear coevolution in a warbler species complex. Nature Communications 12: 4279. Link
(earlier version posted on bioRxivLink )

Mikkelsen, E.K., and D. Irwin. 2021. Ongoing production of low-fitness hybrids limits range overlap between divergent cryptic species. Molecular Ecology 30: 4090-4102. Link
(earlier version posted on bioRxiv: Link )


Wang, S., S. Rohwer, D.R. de Zwaan, D.P.L. Toews, I.J. Lovette, J. Mackenzie, and D. Irwin. 2020. Selection on a small genomic region underpins differentiation in multiple color traits between two warbler species. Evolution Letters 4: 502-515Link
(earlier version posted on bioRxiv: Link )

Irwin, D.E. 2020. Assortative mating in hybrid zones is remarkably ineffective in promoting speciation. American Naturalist 195: E150-E167. Link
(earlier version posted on bioRxiv: Link )


Wang, S., S. Rohwer, K. Delmore, and D.E. Irwin. 2019. Cross-decades stability of an avian hybrid zone. Journal of Evolutionary Biology 32: 1242-1251. Link

Geraldes, A.*, K. Askelson*, E. Nikelski, F.I. Doyle, W.L. Harrower, K. Winker, and D.E. Irwin. 2019. Population genomic analyses reveal a highly differentiated and endangered genetic cluster of northern goshawks (Accipiter gentilis laingi) in Haida Gwaii. Evolutionary Applications 12: 757-772 (*Shared first authorship). Link


Delmore, K.E., J. Lugo, B.M. Van Doren, M. Lundberg, S. Bensch, D.E. Irwin, and M. Liedvogel. 2018. Comparative analysis examining patterns of genomic differentiation across multiple episodes of population divergence in birds. Evolution Letters 2: 76-87. Link

Irwin, D.E. 2018. Sex chromosomes and speciation in birds and other ZW systems. Molecular Ecology 27: 3831-3851. (Invited submission to special issue on “Sex Chromosomes and Speciation”) Link

Irwin, D.E., B. Milá, D.P.L. Toews, A. Brelsford, H.L. Kenyon, A.N. Porter, C. Grossen, K.E. Delmore, M. Alcaide, and J.H. Irwin. 2018. A comparison of genomic islands of differentiation across three young avian species pairs. Molecular Ecology 27: 4839-4855. Link
(PLEASE NOTE: Due to an error in a barcode identification file, the genomic data on the MacGillivray’s and mourning warblers (Geothlypis tolmiei and G. philadelphia) were incorrect. We have now published a correction to those data–see that correction here. This problem does not affect the other species studied in this paper.)

Toews, D.P.L., I.J. Lovette, D.E. Irwin, and A. Brelsford. 2018. Similar hybrid composition among different age and sex classes in the Myrtle-Audubon’s warbler hybrid zone. The Auk: Ornithological Advances 135: 1133-1145. Link

Uy, J.A.C., D.E. Irwin, and M.S. Webster. 2018. Behavioral isolation and incipient speciation in birds. Annual Review of Ecology, Evolution, and Systematics 49: 1-24. Link


Brelsford, A.*, D.P.L. Toews*, and D.E. Irwin. 2017. Admixture mapping in a hybrid zone reveals loci associated with avian feather coloration. Proceedings B 284: 20171106. *Shared first authorship. Link

Kenyon, H.L., M. Alcaide, D.P.L. Toews, and D.E. Irwin. 2017. Cultural isolation is greater than genetic isolation across an avian hybrid zone. Journal of Evolutionary Biology 30: 81-95. Link

Szabo, I., K. Walters, J. Rourke, and D.E. Irwin. 2017. First record of House Swift (Apus nipalensis) in the Americas. Wilson Journal of Ornithology 129: 411-416. Link

Toews, D.P.L., K.E. Delmore, M.M. Osmond, P.D. Taylor, and D.E. Irwin. 2017. Migratory orientation in a narrow avian hybrid zone. PeerJ 5: e3201. Link

Toews, D.P.L., J. Heavyside, and D.E. Irwin. 2017. Linking the wintering and breeding grounds of warblers along the Pacific Flyway. Ecology and Evolution 7: 6649-6658. Link


Delmore, K.E., D.P.L. Toews, R.R. Germain, G.L. Owens, and D.E. Irwin. 2016. The genetics of seasonal migration and plumage color. Current Biology 26: 2167-2173. Link

Fernando, S.P., D.E. Irwin, and S.S. Seneviratne. 2016. Phenotypic and genetic analysis support distinct species status of the Red-backed Woodpecker (Lesser Sri Lanka Flameback: Dinopium psarodes) of Sri Lanka. The Auk: Ornithological Advances 133: 497-511. Link

Grossen, C., S.S. Seneviratne, D. Croll, and D.E. Irwin. 2016. Strong reproductive isolation and narrow genomic tracts of differentiation among three woodpecker species in secondary contact. Molecular Ecology 25: 4247-4266. Link

Irwin, D.E. 2016. A tree of tree frogs around the Black Sea. Molecular Ecology 25: 4093-4096. (invited “Perspective”) Link

Irwin, D.E., M. Alcaide, K.E. Delmore, J.H. Irwin, and G.L. Owens. 2016. Recurrent selection explains parallel evolution of genomic regions of high relative but low absolute differentiation in a ring species. Molecular Ecology 25: 4488-4507 Link

Irwin, D.E., and D.B. Wake. 2016. Ring species. Vol. 3, Pages 467-475 in Encyclopedia of Evolutionary Biology, edited by R. M. Kliman. Oxford: Academic Press. Info

Seneviratne, S.S., P. Davidson, K. Martin, and D.E. Irwin. 2016. Low levels of hybridization across two contact zones among three species of woodpeckers (Sphyrapicus sapsuckers). Journal of Avian Biology, 47: 887-898. Link

Toews, D.P.L., A. Brelsford, B. Milá, C. Grossen, and D.E. Irwin. 2016. Genomic variation across the yellow-rumped warbler species complex. The Auk: Ornithological Advances 133: 698-717. Link

Toews, D.P.L., L. Campagna, S.A. Taylor, C.N. Balakrishnan, D.T. Baldassarre, P.E. Deane-Coe, M.G. Harvey, D.M. Hooper, D.E. Irwin, C.D. Judy, N.A. Mason, J.E. McCormack, K.G. McCracken, C.H. Oliveros, R.J. Safran, E.S.C. Scordato, K.F. Stryjewski, A. Tigano, J.A.C. Uy, and B.M. Winger. 2016. Genomic approaches to understanding population divergence and speciation in birds. The Auk: Ornithological Advances 133: 13-30. Link


Delmore, K.E., S. Hübner, N.C. Kane, R. Schuster, R.L. Andrew, F. Câmara, R. Guigo, and D.E. Irwin. 2015. Genomic analysis of a migratory divide reveals candidate genes for migration and implicates selective sweeps in generating islands of differentiation. Molecular Ecology 24: 1873-1888. Link

Delmore, K.E., H.L. Kenyon, R.R. Germain, and D.E. Irwin. 2015. Phenotypic divergence during speciation is inversely associated with differences in seasonal migration. Proceedings of the Royal Society of London B 282: 20151921. Link

Lee-Yaw, J.A., and D.E. Irwin. 2015. The importance (or lack thereof) of niche divergence to the maintenance of a northern species complex: the case of the long-toed salamander (Ambystoma macrodactylum Baird). Journal of Evolutionary Biology 28: 917-930. Link

Lee-Yaw, J.A.*, T. Sechley*, and D.E. Irwin. 2015. Conflicting effects of microhabitat on long-toed salamander (Ambystoma macrodactylum) movement: implications for landscape connectivity. Canadian Journal of Zoology 93: 1-7. *These authors contributed equally to this work and should both be considered first authorsLink


Alcaide, M., E.S.C. Scordato, T.D. Price, and D.E. Irwin. 2014. Genomic divergence in a ring species complex. Nature 511: 83-85. Link

Delmore, K.E., and D.E. Irwin. 2014. Hybrid songbirds employ intermediate routes in a migratory divide. Ecology Letters 17: 1211-1218. Link

Lee-Yaw, J.A., C.G.C. Jacobs, and D.E. Irwin. 2014. Individual performance in relation to cytonuclear discordance in a northern contact zone between long-toed salamander (Ambystoma macrodactylum) lineages. Molecular Ecology 23: 4590-4602. Link

Szabo, I., S. Cavaghan, G. Hurley, and D.E. Irwin. 2014. A call for the preservation of images, recordings, and other data in association with avian genetic samples, and the introduction of a solution: OMBIRDS. The Auk: Ornithological Advances 131: 321-326. Link

Toews, D.P.L., A. Brelsford, and D.E. Irwin. 2014. Isotopic variation across the Audubon’s–myrtle warbler hybrid zone. Journal of Evolutionary Biology 27: 1179-1191. Link

Toews, D.P.L., M. Mandic, J.G. Richards, and D.E. Irwin. 2014. Migration, mitochondria and the yellow-rumped warbler. Evolution 68: 241-255. LinkPDF


Paxton, K., M. Yau, F. Moore, and D.E. Irwin. 2013. Differential migratory timing of western populations of Wilson’s Warbler (Cardellina pusilla) revealed by mitochondrial DNA and stable isotopes. Auk 130: 689-698. LinkPDF


Delmore, K.E., J.W. Fox, and D.E. Irwin. 2012. Dramatic intraspecific differences in migratory routes, stopover sites and wintering areas revealed using light-level geolocators. Proceedings of the Royal Society of London B 279: 4582-4589. LinkPDF

Irwin, D.E. 2012. Local adaptation along smooth ecological gradients causes phylogeographic breaks and phenotypic clustering. American Naturalist 180: 35-49. LinkPDF

Irwin, D.E. 2012. Culture in songbirds and its contribution to the evolution of new species. Pages 163-178 in: Creating Consilience: Integrating the Sciences and the Humanities, edited by E. Slingerland and M. Collard. Oxford University Press, Oxford. (Note that this paper includes some interesting details on song variation in the greenish warbler ring species; see the book for the definitive version, or download a preprint here)

Irwin, D.E. 2012. A novel approach for finding ring species: look for barriers rather than rings. BMC Biology 10: 21. (invited Commentary) LinkPDF

Irwin, D.E. 2012. Look northward to the boreal, the home of many migrating birds. Frontiers of Biogeography 4: 99-101. (book review) Link

Lee-Yaw, J.A., and D.E. Irwin. 2012. Large geographic range size reflects a patch-work of divergent lineages in the long-toed salamander (Ambystoma macrodactylum). Journal of Evolutionary Biology 25: 2276-2287. LinkPDF

Safran, R., S. Flaxman, M. Kopp, D.E. Irwin, D. Briggs, M.R. Evans, W.C. Funk, D.A. Gray, E.A. Hebets, N. Seddon, E. Scordato, L.B. Symes, J.A. Tobias, D.P.L. Toews, and J.A.C. Uy. 2012. A robust new metric of phenotypic distance to estimate and compare multiple trait differences among populations. Current Zoology 58: 426-439. Link

Seneviratne, S.S., D.P.L. Toews, A. Brelsford, and D.E. Irwin. 2012. Concordance of genetic and phenotypic characters across a sapsucker hybrid zone. Journal of Avian Biology 43: 119-130. LinkPDF

Toews, D.P.L., and A. Brelsford. 2012. The biogeography of mitochondrial and nuclear discordance in animals. Molecular Ecology 21: 3907-3930. Link

Toews, D.P.L., D.E. Irwin, S.J. Hejl, J.A. Holmes, and D.E. Kroodsma. 2012. Pacific Wren (Troglodytes pacificus). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.


Brelsford, A., B. Milá, and D.E. Irwin. 2011. Hybrid origin of Audubon’s warbler. Molecular Ecology 20: 2380-2389. LinkPDF

(This paper is the subject of a “News and Views”: Jacobsen & Omland. 2011. Increasing evidence of the role of gene flow in animal evolution: hybrid speciation in the yellow-rumped warbler complex. Molecular Ecology 20: 2236-2239. Link)

Irwin, D.E., J.H. Irwin, and T.B. Smith. 2011. Genetic variation and seasonal migratory connectivity in Wilson’s Warblers (Wilsonia pusilla): species-level differences in nuclear DNA between western and eastern populations. Molecular Ecology 20: 3102-3115. LinkPDF

Kenyon, H.L., D.P.L. Toews, and D.E. Irwin. 2011. Can song discriminate between MacGillivray’s and Mourning warblers in a narrow hybrid zone? Condor 113: 655-663. LinkPDF

Rohwer, S., and D.E. Irwin. 2011. Molt, orientation, and avian speciation. Auk 128: 419-425. LinkPDF

Toews, D.P.L., A. Brelsford, and D.E. Irwin. 2011. Hybridization between Townsend’s and black-throated green warblers in an avian suture zone. Journal of Avian Biology 42: 434-446. LinkPDF


Kuker, K., and L. Barrett-Lennard. 2010. A re-evaluation of the role of killer whales Orcinus orca in a population decline of sea otters Enhydra lutris in the Aleutian Islands and a review of alternative hypotheses. Mammal Review 40: 103-124.


Brelsford, A., and D.E. Irwin. 2009. Incipient speciation despite little assortative mating: the yellow-rumped warbler hybrid zone. Evolution 63: 3050-3060. LinkPDF

Irwin, D.E. 2009. Speciation: New migratory direction provides route toward divergence. Current Biology 19: R1111-R1113. (invited “Dispatch”) LinkPDF

Irwin, D.E. 2009. Incipient ring speciation revealed by a migratory divide. Molecular Ecology 18: 2923-2925. (invited “Perspective”) LinkPDF

Irwin, D.E., A. Brelsford, D.P.L. Toews, C. MacDonald, and M. Phinney. 2009. Extensive hybridization in a contact zone between MacGillivray’s and mourning warblers (Oporornis tolmiei and O. philadelphia) detected using molecular and morphometric analyses. Journal of Avian Biology 40: 539-552. LinkPDF

Irwin, D.E., A.S. Rubtsov, and E.N. Panov. 2009. Mitochondrial introgression and replacement between yellowhammers (Emberiza citrinella) and pine buntings (E. leucocephalos; Aves, Passeriformes). Biological Journal of the Linnean Society 98: 422-438. LinkPDF

Rush, A., R.C. Cannings, and D.E. Irwin. 2009. Analysis of multilocus DNA reveals hybridization in a contact zone between Empidonax flycatchers. Journal of Avian Biology 40: 614-624. LinkPDF


Irwin, D.E., M.P. Thimgan, and J.H. Irwin. 2008. Call divergence is correlated with geographic and genetic distance in greenish warblers (Phylloscopus trochiloides): a strong role for stochasticity in signal evolution? Journal of Evolutionary Biology 21: 435-448. LinkPDF

Toews, D.P.L., and D.E. Irwin. 2008. Cryptic speciation in a Holarctic passerine revealed by genetic and bioacoustic analyses. Molecular Ecology 17: 2691-2705. LinkPDF


Irwin, D.E., and M. Hellström. 2007. Green Warbler Phylloscopus (trochiloides) nitidus recorded at Ottenby, Öland: a first record for Scandinavia. Ornis Svecica 17: 75-80. PDF


Bensch, S., D.E. Irwin, J.H. Irwin, L. Kvist, and S. Åkesson. 2006. Conflicting patterns of mitochondrial and nuclear DNA diversity in Phylloscopus warblers. Molecular Ecology 15: 161-171. PDF


Irwin, D.E., S. Bensch, J.H. Irwin, and T.D. Price. 2005. Speciation by distance in a ring species. Science 307: 414-416. PDF

Irwin, D.E., and J.H. Irwin. 2005. Siberian migratory divides: the role of seasonal migration in speciation. Pages 27-40 in Birds of Two Worlds: The Ecology and Evolution of Migration, edited by R. Greenberg and P. P. Marra. Johns Hopkins University Press. PDF (large file: 3.7 MB)


Irwin, D.E., and J.H. Irwin. 2004. Speciation in a ring: the role of song. Page 204 in Nature’s Music: the Science of Birdsong, edited by P. Marler and H. Slabbekoorn. Academic Press.


Price, T.D., A. Qvarnström, and D.E. Irwin. 2003. The role of phenotypic plasticity in driving genetic evolution. Proceedings of the Royal Society of London B 270: 1433-1440. PDF


Bensch, S., S. Åkesson, and D.E. Irwin. 2002. The use of AFLP to find an informative SNP: genetic differences across a migratory divide in willow warblers. Molecular Ecology 11: 2359-2366. PDF

Irwin, D.E. 2002. Phylogeographic breaks without geographic barriers to gene flow. Evolution 56: 2383-2394. PDF

Irwin, D.E. 2002. Ring species: unusual demonstrations of speciation. Electronic publication on the ActionBioscience web site:

Irwin, D.E., and J.H. Irwin. 2002. Circular overlaps: rare demonstrations of speciation. Auk 119: 596-602. (invited “Overview”) PDF

Åkesson, S., S. Bensch, A. Hedenström, and D.E. Irwin. 2002. Blowfly Trypocalliphora braueri (Diptera: Calliphoridae) larvae infestation in Willow Warblers Phylloscopus trochilus breeding in a hybrid zone. Ornis Svecica 12: 83-88.


Irwin, D.E., P. Alström, U. Olsson, and Z.M. Benowitz-Fredericks. 2001. Cryptic species in the genus Phylloscopus (Old World leaf warblers). Ibis 143: 233-247. PDF (large file: 12.4 MB)

Irwin, D.E., S. Bensch, and T.D. Price. 2001. Speciation in a ring. Nature 409: 333-337. PDF

Irwin, D.E., J.H. Irwin, and T.D. Price. 2001. Ring species as bridges between microevolution and speciation. Genetica 112-113: 223-243. (Also as part of a book: Pages 223-243 in Microevolution: Rate, Pattern, Process, edited by A.P. Hendry and M.T. Kinnison. Kluwer Academic Publishers, Dordrecht, The Netherlands) PDF


Irwin, D.E. 2000. Song variation in an avian ring species. Evolution 54: 998-1010. PDF


Irwin, D.E., and T. Price. 1999. Sexual imprinting, learning and speciation. Heredity 82: 347-354. PDF