Sunday 28 January 2007

A plague of crows - dead or alive

Crows get rid of rotting food; they are good for the hygiene of the city, right? Well, read on:

One day in 2001 I stood in Brighton Road, Highgate Hill, Brisbane, and looked across the patch of land which is bounded by Appel Street, Vulture Street, Franklin Street, and back to Brighton. I counted 20 crows. As anyone can confirm standing in the same place this must be on the low side because of so many blind spots. Anyway, using a street directory it turns out that the patch measures 0.15 by 0.25km, or 0.0375sqkm; in other words, there were 20 crows per 0.0375sqkm.

If we look at the map of entire Brisbane and take an area which is defined in the southeastern corner by Shailer Park, in the southwest by Redbank, and in the northwest by Bray Park, we get a rectangle which has its northeastern tip over the water somewhere off Mud Island. But that's fine since we left out large sections in the east towards Redland Bay and in the north towards Redcliffe; therefore the resultant 1000sqkm would be on the conservative side. Dividing those 1000 by 0.0375 (the Highgate Hill patch) gives us 26,667, and multiplying this figure by 20 (the number of crows counted) results in 533,333 crows for the Brisbane area.

Now we know that crows can live to the age of 35, but assuming a median value of 25 years seems reasonable since we are dealing with animals in the wild. Therefore we can say that it takes approximately 25 years for over 500,000 birds to die off. Divide 533,333 by 25 and we get 21,333, which is the number of crows dying every year; this means 1778 crows per month. If the average crow weighs 0.55kg, the above amount translates to 978kg.

It is believed that in Brisbane the crow population has reached its plateau, although the last ten years saw a dramatic increase in their numbers. Let's say this happened five years ago, in which case every single month from about 2025 onwards the people of Brisbane will endure a mass of dead crow flesh to the tune of almost one ton spread across their city.

There you have it. The above assumes the birth and death rates are steady, but they are not if the population is still rising. This may well be the case because the human population is increasing and the main food source for the birds is the rubbish we generate. Then these figures are just the start and a larger fallout from their corpses is yet to come. And by the way, there are many areas where the pro rata crow numbers would be much greater. For example, there once was a colony of about 50 crows in one (!) of the trees at the University of Queensland.

Feel free to check the figures for accuracy.

By the way, so far there has been no response from the Lord Mayor or from Professor Jones.

And here's something else:

As it happens, on Friday 26th the Brisbane metropolitan daily, The Courier Mail, ran an article about sounds painful to humans, "Vomiting tops the sound of pain list". As the title suggests, regurgitating is the most repulsive of them all. Professor Trevor Cox from the University of Salford in the UK did not include crows in his survey, otherwise the birds' ability to simulate the gagging sound immediately preceeding the actual vomiting would have featured as well. It's part of their repertoire.

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