This is mostly for Colibri’s response, but others can feel free to join in, in classic GQ discussion mode.
Most bird orders make at least remote sense to me, even if “common sense” rebels at things like woodpeckers, toucans, and hoopoes in the same order. But what unites the members in each of two orders is totally baffling to me. Those would be Gruiformes and Apodiformes.
Apodiformes is a group that consists entirely of the swifts and the hummingbirds. The closest thing to sense I can make of them is that both groups are specialized for aerial acrobatics in pursuit of their daily nourishment. But that’s not a valid taxonomic reason, founded in anatomy and evolutionary trends.
Gruiformes is even odder: the cranes (which look like they ought to be in with the herons, egrets, flamingos, and storks), the rails (which frankly I can make no sense of), the bustards (ditto), and miscellaneous other groups that seem to have very little in common aside from being birds.
Care to expound on them? (If you feel like doing Piciformes as well, I’d consider that gravy.)
Apodiformes is actually a very well supported group anatomically. The swifts and the hummingbirds share a unique kind of modification to the wing and shoulder girdle. Recent genetic work has confirmed this monophyly.
Look at some pictures, and you will see that both groups have an extremely shortened humerus, or upper arm, along with a very elongated distal part of the wing. This probably contributes to their ability for rapid wing beats.
Interestingly, hatchling hummingbirds have very short beaks, much like those of swifts. They seem to be descended from swift-like birds that specialized on nectar as a food source.
That one I’ll have to get back to you on after checking on the current state of play. Gruiformes has long been a kind of grab-bag order for odd things that didn’t fit very well elsewhere.
A quick check doesn’t suggest that there is a lot of consensus yet on Gruiformes. There is apparently no single diagnostic morphological feature that unites them. Genetic work suggests that not all the groups belong together, but several of the families seem to be ancient relicts, and it’s difficult to sort out which groups they actually are aligned to.
Some of the traditional gruiform families have been moved to other Orders based on genetics, while some of the core groups do actually seem to be related to one another. But to some extent the current Order is maintained due to inertia.
FWIW recordings I have heard of the twitters some hummingbirds make sound to me not dissimilar to the sounds Chimney Swifts make (the only swift I am really familiar with).
You can see a great picture of the relatively short, stubby beaks of some humminbird hatchlings here.
A couple of years ago there was a nice sequence of pictures taken at the same nest over several weeks, the change in the beaks of the nestlings over a short period of time was amazing. I can’t seem to find the pictures again just yet.
Interestingly, hummingbirds actually sing, although it’s often so high-pitched it’s hard to recognize. Hummingbirds, along with the parrots and the higher passerines (songbirds), are the only group known to learn songs, rather than having them be innate.
There are organisms whose classification is so uncertain that they have a special term: Incertae sedis—“of uncertain position (seat)”
I’ve been reading about this because I have a pair of bananaquits (Coereba flaveola) that are very hummingbird-like, but whose exact classification is uncertain.
Thanks, Colibri (and others). So essentially my “lifestyle” inference about aerial acrobatics in the Apodiformes is borne out by physical adaptations for rapid wingbeat, etc.?
I’m surprised about the Gruiformes – I thought it was pretty common practice for taxonomically inclined biologists to address these sorts of things, and propose alternate solutions, one of which ends up being accepted. (As with the former mammalian Order Insectivora, something of a grabbag and now parceled out among several orders.)
Yes. The two groups have the most extreme adaptations to powered flight in birds. Swifts can sleep on the wing, and also copulate in flight. Some may fly continuously for days on end. Hummingbirds of course are well known for their acrobatic capabilities, being not only able to hover but also fly backwards.
Yes, they do, but birds are morphologically rather homogeneous and it can be difficult to figure out relationships from skeletal characteristics alone. Research on genetics has overturned much of what we thought we knew about relationships among higher bird groups based on morphology. With ancient groups such as some “gruiform” lineages it can be very diffucult to resolve what may be shared primitive conditions (which cannot be used to define clades) and what may be derived, and used to unite groups.
Likewise, when a group has undergone a rapid radiation in the far past it may be impossible to resolve the actual order of branching of lineages from genetic data. Variation in the rates of the “molecular clock” in different lineages may make this impossible to sort out.
At the North American Ornithological Congress I attended last year, one taxonomist discussed the so called “Wall of Death” in avian taxonomy. Many of the higher groups branched off so close to each other in the past that the differences can’t be resolved by tree-building algorithms, producing a long horizontal line from which many orders branch.
The Bananaquit has been bounced around from family to family for years, having been placed in the Honeycreeper family, then with the Wood-Warbers, and finally in its own family by itself. Interestingly, recent genetic work has rather surprisingly indicated that the Bananaquit is actually related to the buntings and sparrows (Family Emberizidae), being closest to the Yellow-faced Grassquit.