Cormorants, and the evolution of birds

I thought the bird I saw on Coogee beach was somewhat duck-like in size and shape - except that it held its chest high, and had a sharp beak and rather large webbed feet.  Obviously a fisher.  It was entirely black (including feet), save yellow markings around the eyes.

It was actually a Great Cormorant (Phalacrocorax carbo), a widespread native to Australia.

Birds are most closely related to crocodilians, in the dinosaur clade archosauromorpha.  (Reptiles, thus, are paraphyletic - not really a true, complete evolutionary grouping, and rather just a description).

But let's take it from the top.  Or, at least, the beginning of the mesozoic (the "middle", or dinosaur era of 250 - 65 million years ago).  Archeosaurs (the precursor group to archosauromorphs) arguably became more successful at the time than synapsids (mammal ancestors) because they were better suited to the dryness of the Triassic period (250 - 200mya).  They included dinosaurs, crocodilians, and the ancestors of birds.  Crocodilians first appeared about 84mya (late Cretaceous).  Modern birds (neornithes: feathers, no teeth, hard eggs, several flight adaptions) evolved into a variety of forms in the Cretaceous (145-65mya).  The two bird groupings, palaognathae (comprising ratites - most of the flightless birds - plus the barely-flying tinamous) and neognathae (the rest) probably arose before the KT meteor event of 65mya, but radiated into the numerous different species mostly afterwards.

Now, the reason that cormorant looked a bit duck-like to me was its webbed feet and the shape and size of its body.  But they are not related at all.  Cormorants have been grouped together as pelecaniformes (which includes the pelican's family pelicanidae), while ducks are in the anseriforme order.

Although Colin Tudge (in The Variety Of Life) is happy enough with the cormorant's above classification, Wikipedia casts doubt on pelecaniformes being a true clade (that is, a single complete evolutionary grouping), and suggests phalacrocoraciformes as a more properly monophyletic clade.  The issue here is that the pelecaniforme was used to encompass all birds with fully four webbed toes.  But as we know, classification based on such a stark physical trait is dangerous, since the various species could easily have evolved separately but convergently.  If the purpose (webbed feet for paddling) is so clearly useful, that evolutionary change could have happened several times, several locations.

The names cormorant and shag are sometimes used interchangeably, but even when each is called by its proper name, there is no consistency between them.  Their collected family name is Phalacrocoracidae - but the discussion there concludes that this is not one consistent evolutionary grouping.

The cormorant I encountered was not well, if it was so near humans.  It was wandering around, not flying, and unlike the one above had most of its tail feathers missing - and appeared far too tame for its own good.  It and kids were a danger to each other.  I contacted the wildlife rescue organisation WIRES, who recommended taking it to a vet that was on the Wires register; so I took it to Struggletown in Randwick.  Unfortunately, it died within the next two days - as a result of lead poisoning.  How?  Unknown, and this was not the first bird specimen to be sent off for analysis for this issue.  Also not known what the missing tailfeathers had to do with its plight.  I was told the apparent tameness was due to lack of interaction with humans.  Still, it was the indirect effect of human activity that got it in the end.

A mynah with a tail feather

Yes, the common mynah does normally have tail feathers. We see a lot of them in our back yard. But this morning I saw one with an extra tail feather.




It's a large white feather, attached to the mynah's tail. I figured the feather came from a cockatoo - they're they only white birds abundant in this area.

And the feather was firmly stuck - I saw the mynah fly up to a tree a couple of times, and the feather stayed with it, more or less straight in alignment. I daresay the extra baggage must have either helped or hindered the mynah's flight, but I didn't see any evidence either way.

So, the question is: was it an accident, self-decoration, or did someone put it there? I would guess the former, although it seemed so firmly attached as to suggest the latter. Then again, has any ornithologist heard of a mynah decorating their own tail?

Birds, ratites, moas, kiwis, predators

This is a story about native New Zealand birds and animals, one that gets more interesting as it goes.

First, I'll start by drilling down through the origin of birds.

Birds are members of the taxonomical class Aves, and are the only living descendants of dinosaurs.  The earliest recognised Ave is the archaeopteryx, dates from the Jurassic period, about 250 million years ago (mya). As a result of the dinosaur-killing KT meteor 65 mya, most near relatives are gone: apart from birds (as descendants), the closest remaining relatives to dinosaurs are the crocodilians. In fact, what we now know as birds are the Avian sub-class Neornithes, and are not direct descendants of the archaeopteryx.

The earliest division of modern birds is between the two superorders Palaeognathae - nearly all are ratites - and Neognathae - the rest. Ratites (properly, the order Struthioniformes) are effectively one of the oldest surviving avian lineages - and they're all flightless, descending from a flying ancestor but at some point no longer needing to fly.

Not all flightless birds are ratites. Many different bird families have evolved flightlessness on islands, where they have found themselves with no predators. Richard Dawkins notes that rails in particular "lend themselves to island-hopping followed by flightlessness".

Why lose flight? Colin Tudge: "flight ... exacts an enormous price. It requires commitment from the entire anatomy, and a huge input of energy".

Ratites are the most well-known of the flightless birds, encompassing the ostrich, emu, cassowary, rhea, kiwi, moa, and extinct elephant bird. Between them, they represent pretty well all the current pieces of the old southern land mass Gondwana. That suggests survivability of this grouping, even when exposed to predators. Some were pretty large, though, but perhaps ironically the largest ones, Madagascar's elephant bird and New Zealand's moa, survived only until the last millenium - finally a victim of the greatest predators, humans. The elephant bird was the heaviest bird ever, at up to 500kg and three metres tall.

cassowary

The ostrich is hard to place, but Dawkins reckons it was with the elephant bird when India and Madagascar became isolated from the rest of Gondwana then, like other species, took the fast "Indian ferry to Asia", later to take a slow way back to Africa.

Moas diverged from the rest only about 80 mya - when New Zealand split from Gondwana. A couple of notes about their traditional representation in New Zealand: first, they did not tend to hold their heads fully erect, as you see in the museums. Rather, the head was closely level with the body, for browsing. Second, one of their predators was something called Haast's Eagle, the largest eagle that ever lived. This extinct giant eagle is something I certainly never heard about growing up in New Zealand. Intriguing.

Anyway, given the robust ratite's story, you'd expect the kiwi to be closely related to the moa. Well, it's not. It's closer to the emu and cassowary, both from Australia and New Guinea. Dawkins suggests the kiwi arrived in New Zealand via New Caledonia.

kiwi

It's worth considering the effects of predation over time.  For the elephant bird and moa, size was a boon, but ultimately the source of their demise as they became relatively fearless. For the kiwi, nocturnalism may have been a recent survival mechanism; yet Wikipedia notes that in predator-free sanctuaries, the notoriously nocturnal kiwi is often seen in the daytime. For others, speed has been on their side.

I mention all this to help give context to the unusual 19myo mouse-size SB mammal fossil (discussed here and here) recently found in NZ. Predation has to be a significant issue in the story. How did it survive 60 million years in NZ? What size changes might have happened to avoid predation in a land of bird seeking small morsels? Why did they ultimately disappear? This species doesn't seem to have had any impact on the NZ story as it is known so far...



Reference
Dawkins, Richard (2004): An Ancestor's Tale. Phoenix, London.
Tudge, Colin (2000): The Variety of Life. Oxford University Press, Oxford.