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I've talked to a couple of researchers today and read recent articles on the subject of hybridization of Darwin's finches. I'm confused about the consensus in the scientific community.

First, I was reading about hybridization in systems where adaptive radiation occurred. I came across this Honeycreepers paper: Knowlton, J. L., D. J. Flaspohler, N. C. R. Mcinerney, and R. C. Fleischer. 2014. First Record of Hybridization in the Hawaiian Honeycreepers: 'I‘iwi ( Vestiaria coccinea) × ’Apapane ( Himatione sanguinea). The Wilson Journal of Ornithology 126:562–568.

In this paper they are saying:

The Galápagos finches, for instance, hybridize frequently both within and across genera (Grant et al. 2004, Grant and Grant 2008).

But in the resources they cite, here is what I found:

Rare hybridization between the species, occurring partly as a result of misimprinting on song (Grant and Grant 1998)

From Grant, P. R., B. R. Grant, J. A. Markert, L. F. Keller, and K. Petren. 2004. Convergent evolution of Darwin's finches caused by introgressive hybridization and selection. Evolution 58:1588–1599.

Hybridization was rare at the level of individuals: only a few percent of all offspring are hybrids

From Bell, G. 2015. Every inch a finch: a commentary on Grant (1993) 'Hybridization of Darwin‘s finches on Isla Daphne Major, Galapagos’. Philosophical Transactions of the Royal Society B: Biological Sciences 370:20140287–20140287.

Hybridization was always rare.

From Grant, P. R. 1993. Hybridization of Darwin's Finches on Isla Daphne Major, Galapagos. Philosophical Transactions of the Royal Society B: Biological Sciences 340:127–139.

Hybridization occurs rarely (less than 2% of breeding pairs) but persistently across years, usually as a result of imprinting on the song of another species.

In Grant, B. R., and P. R. Grant. 2008. Fission and fusion of Darwin's finches populations. Philosophical Transactions of the Royal Society B: Biological Sciences 363:2821–2829.

Did I miss something, or is hybridization rare and not frequent? Maybe frequently is so vague that it includes, rare?

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I actually just had to read a Grant & Grant paper, so hopefully, I can get this right. My understanding is that hybridization events have repeatedly seen to occur, but the events themselves usually do not repeat within a lineage, i.e. once a lineage becomes partially hybridized, it is unlikley to continue to breed with adjacent populations.

Due to the reproductive barriers that come from song patters of hybridized individuals (Grant & Grant, 2009), Repeated hybridations are unlikely to occur within a lineage, even when in the presence of a species with which hybridization can occur.

Grant, P.R. and B.R. Grant. 2009. The secondary contact phase of allopatric speciation in Darwin's finches. PNAS 106 20141-20148

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    $\begingroup$ Please cite the Grant & Grant paper. We strongly encourage the addition of sources here at Biology. $\endgroup$
    – AliceD ♦
    Apr 5, 2017 at 22:06
  • $\begingroup$ That's what I was thinking: "Galápagos finches have very low, but persistent, levels of hybridization events, compared to other system where speciation is near completion or completed or where there is high reproductive isolation" For the actual numbers and percentages of hybrids see: Grant, P. R. 1993. Hybridization of Darwin's Finches on Isla Daphne Major, Galápagos. Philosophical Transactions: Biological Sciences 340:127–139. $\endgroup$
    – M. Beausoleil
    Apr 5, 2017 at 22:11

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