Products of Kinky Inter-species Sex

Um, maybe I don't want to know what sort of Google search will hit that post title, or who's doing the searching. I can assure you, the following post is both PG and work-safe.

I came across this post today on identifying a hybrid passerine bird. The bird in question is an entirely different individual from the one discussed here, which was also revealed not too long ago. (Offhand, the site linked to via the latter, Don Roberson's Creagrus, is well worth a look for anybody interested in birds.)

Both of these birds belong to the family Parulidae, the so-called American 'warblers' - an entirely distinct and unrelated family from the various 'warblers' of the Old World (previously Sylviidae, but see here - Don Roberson again - for a good summary of the collapse of that family) and from the Australasian 'warblers' of the family Acanthizidae. Interestingly, Parulidae seems to have produced a large number of recorded hybrids over the years (enough that many have been awarded their own common names), and attention has been drawn to the fact that a greater number of recorded hybrids have been between members of different genera than members of the same genus (those that are members of the same genus have invariably been very closely-related species). The same pattern has been recorded in South American manakins (Pipridae) (Stotz, 1993). Even if we admit the point that a 'genus' is simply a grouping defined by the author and has no objective reality, it still remains arguable that hybrids are always between very closely or distantly related species, never between fairly closely related species.*

*My apologies for the revoltingly turgid sentence.

Parkes (1978) commented on this phenomenon, and suggested that barriers to hybridisation may be more heavily selected for between closely-related and sympatric species for which hybridisation may be more of a risk. This theory has also been supported by work on courtship songs in insects where sympatric species of lacewing have very different songs, while different species from Asia and North America have very similar songs, and members of one species will actually respond if they hear songs from the other 'wrong' species (Henry et al., 1999).

Perhaps the best comment on all this, though, comes from my partner - when I told him that I was posting on an interspecific hybrid, he seemed rather incredulous that a bird had mated with a member of a different species, and when considering why commented, "that must be one ugly bird".

REFERENCES

Henry, C. S., M. L. Martínez Wells & C. M. Simon. 1999. Convergent evolution of courtship songs among cryptic species of the carnea group of green lacewings (Neuroptera: Chrysopidae: Chrysoperla). Evolution 53 (4): 1165-1179.

Parkes, K. C. 1978. Still another parulid intergeneric hybrid (Mniotilta × Dendroica) and its taxonomic and evolutionary implications. The Auk 95: 682-690. Pdf here.

Stotz, D. F. 1993. A hybrid manakin (Pipra) from Roraima, Brazil, and a phylogenetic perspective on hybridization in the Pipridae. Wilson Bulletin 105 (2): 348-351. Pdf here.