Archive for the ‘Birds’ Category

So, Happy New Year to everyone reading this! I hope you all have already abandoned your well meaning but futile New Year’s Resolutions; because let’s face it, none of us were going to end up ‘spending a hour at the gym every day’ whilst Youtube still exists.

Sorry I haven’t updated earlier, but this was for two reasons. Firstly, your anguish nourishes me, and secondly I had a dissertation to hand in. It’s all over now though, and it would be utterly and completely pointless to keep on thinking about what mark it would get. Worrying about it, as I spend five hours telling my flatmate the other day, is pointless and will only make it worse, and really the silliest thing I could do would be to keep on thinking about it, and wondering how it went. In fact, I’m not even worried about it at all, and I barely think about how it went, because that would be silly and pointless. I’ve also been doing an advanced statistics course, which is a bit of a slog for me, as I get confused by sums which have both letters and numbers in them. Still, it would keep me from worrying about how my dissertation went, if I was thinking about it at all, which I am not. Imagine being stupid enough to keep on thinking about something you can’t change.

Anyway, enough blather! The Horrific Animal of the World featured today is the Cowbird.

Before we go any further, yes, birds can be horrific animals too. Robins (Erithacus rubecula), those cute little critters featured on Christmas cards, are so aggressive that the males will attack pretty much anything with a streak of red in them, thinking it to be rival male (http://www.rspb.org.uk/wildlife/birdguide/name/r/robin/territory.aspx) – there have been reports of male robins even attacking their own reflections in a window. In the nest, chicks frequently ‘compete’ for food. In some cases, this competition simply takes the form of the older and stronger siblings getting all the food. In the case of many birds, however, straight-up siblicide occurs. Sometimes, this happens when there is simply not enough food to go around (Facultative siblicide), and so the weaker one is killed (in the case of the Blue-footed Booby (Sula nebouxii), for instance, the female lays ‘too many’ eggs for the average food supply; in case the year turns out to be better than average.) Rather more creepily, as is the case of many eagle species, the older chick in the nest always (or nearly always) kills the younger (Obligate siblicide), no matter how much food is available – indeed, the extra egg is really only insurance (Anderson 1990). The Black Eagle (Ictinaetus malayensis)  is especially aggressive – in one study, the younger chick was pecked more than 1500 times in three weeks before it expired; and out of two hundred studied cases, there is only one where both Black Eagle chicks reached maturity (Mock, Drummond and Stinson, Avian Siblicide).

Birds can also be pretty awesome, as well. The obvious examples are falcons, which swoop down on their prey whilst both are still in the air, and Eagles (after they’ve grown out of their ‘murdering their siblings’ phase, at least). But there are more.

Secretary birds trample their favourite prey (which should be noted are venomous snakes) to death by stamping on them. Here is a poor-quality Youtube video, probably with witless homophobic comments, proving my point. http://www.youtube.com/watch?v=QJKBPyavWlI

The Corvidae (which includes the ravens, crows and magpies) are so terrifyingly intelligent that they would probably run civilisation rather better than we do, even though they would doubtless be indifferent to our shrieked and futile pleas for mercy. They are  really quite unsettlingly clever. I would devote the entire blog to how brilliant these birds are, actually, but I would not be able to do them justice, and then my fate would be indescribable.

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The King of All Ravens (species Corvus corax) decides to let the human apes live another year after deciding our petty wars ‘amuse Him’. (Picture Credit: Wikimedia Commons)

So yes, birds can be both sinister and kind of cool as well, rather like the Mafia in the Godfather. But Cowbirds? Really? I mean, the name makes them sound rather like fat, kind-of-cute-in-a-dumb-sorta-way balls of feathers. So how on Earth do Cowbirds feature here?

Well, the thing is these Cowbirds are less “Daisy-the-Brown-and-White-Cow” and more “The [bleeping] vicious bull that lurks in the field and hungers for the blood of hikers”, except considerably more intelligent and Don Coroleone-y. In fact, they are a combination of the most sinister aspects of birds (you know, the whole killing infants thing) but a little bit of the cleverness the Crows have, coupled with the originality of the Secretary Bird. Really, they would have been better named ‘Coroleonebirds’, because they are, in fact, the avian equivalent of the Mafia.

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“What does it mean?”
“It means Luca Brasi sleeps with the fishes. Also, its lunchtime”
(Photo credit http://www.cornishseatours.com/)

This is not hyperbole on my part, either. Scientists actually use the term ‘Mafia Hypothesis’ to describe how these birds act. See, Cowbirds are rather like Cuckoos, in that they lay their eggs in other bird’s nests. The Common Cuckoo (Cuculus canorus) uses a wide variety of techniques to get other birds to do the whole ‘chick-rearing’ thing. Its eggs are adapted to resemble those of the birds it most frequently parasitizes, with different groups laying different egg designs. Female cuckoos can hold their eggs inside them for an extra 24 hours; this means that when the egg is eventually laid in a host nest, the chick hatches rapidly and can chuck out the original eggs, because if there is one thing birds apparently love, its infanticide. It’ll also do this to any already hatched chicks in the nest too. Despite the fact the chick rapidly grows to be bigger than both of its parents, the hosts continue to feed it. Its begging calls are such that it mimics the begging cries of a whole nest of host chicks; effectively getting all the food that would be going to all of the hosts’ offspring (Davies et al 1998). For this behaviour of infanticide, exploitation and deceit, it gets a faintly annoying clock named after it.

The Brown Headed Cowbird (Molothrus ater) also practises ‘Brood parasitism’, much like the cuckoo. However, it lacks some of the clever adaptations the cuckoos have to fool other birds, such as eggs which are almost identical to those of the host species. Also, it is slightly less murderous, the chicks of the cowbird not always killing the chicks of the host; this bit will become important later. Obviously, the reproductive success of the host is rather reduced if it has a bloody great parasite in its nest, eating all the food meant for its chicks. Therefore, there is a strong selective pressure to simply kill the Cowbird chick. And this is where things get interesting. If the parent cowbird sees her little bundle of joy being maltreated, she swoops in and destroys the host’s nest (and eggs) too, in retaliation. Therefore, it is thought that this makes some hosts accept the Cowbird chick, rather than running the risk of losing their whole clutch of eggs. In one study, nests that accepted the cowbird chick were destroyed only 6% of the time, but if the chick was ejected, the nest ran almost a 50:50 chance of being destroyed (Hoover et al 1997), thus proving that threats will always suffice if no other option is possible. Threats like, I don’t know, my dissertation being marked as ‘late’ for some reason…

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“Nice nest. It would be a shame if something happened to it, and those lovely eggs of yours. Capiche?”
Photo credit: Wikimedia Commons