Monday, February 21, 2011

3360 Caterpillars

You can do this search yourself.  Go to Google Books and type in "3360 Caterpillars." You will get close to two hundred results. What exactly is going on? The answer leads us one of the first and most important pieces ever written in respect to the protection of birds and one which would eventually help to change the North American bird landscape forever (not necessarily for the better).

 The key text is a 1723 letter to Richard Bradley published in his General Treatise on Husbandry & Gardening--perhaps the first true agricultural periodical. I've embedded the Google Books version below.

The letter, from an un-named correspondent, "S.C.," begins:
Reading lately Mr. Mortimer's Treatise of Husbandry, I took notice of his remarkable prejudice against the winged species, insomuch as to wish for a law for extirpating several tribes of them.
We begin in the middle of a conversation. Mr. Mortimer has stated his opinion--kill off the destructive birds, in fact make it a law requiring farmers to do so.  I've been unable to find the exact text referenced here [see bottom of page] but Mortimer elsewhere displays a matter-of-fact attitude toward the destruction of putatively harmful birds. In his 1707 book, The Whole Art of Husbandry, he lists "work to be done in the orchard and kitchen garden" for January:
Prune vines and forward fruit trees: if the weather be open and mild, dig and trench Gardens...Set Traps to destroy Vermin where you sow and have such plants or seeds as they will injure. Take fowls; destroy sparrows in barns, and near them kill bullfinches, etc. [my emphasis]
Indeed, Mortimer's position might be considered the leading position, and an ancient one at that. As early as 1533 we can see an act of Parliament promoting the destruction of "choughs [jackdaws], crows, and rooks." By the 1700s, agricultural communities would establish "sparrow clubs" aimed at eliminating this particular threat to their crops.

S.C., however, wants to inject a different perspective into the conversation.  In doing so he will introduce a number of arguments and rhetorical figures used one hundred, even two hundred years later in service of bird protection.

I shall in this beg leave to be an advocate for these innocents who cannot speak for themselves; and endeavour to show, that the services they do us, abundantly balance the inconveniences, and that instead of being nuisances they are blessings, and that without them, we should be like the Land of Egypt under the Curse, that the grasshoppers would come, and caterpillars innumerable, and would eat up all the grass in our Land, and devour the fruit of our ground, and multiply so exceedingly, as to creep into our Kings' palaces; and flies would so abound, as to be extremely incommodious to us.

>Without much elaboration it is useful to notice the following:

  1. That birds--indeed animals of all kinds--are "dumb innocents" who need humans to speak for them--a key figure in early anti-cruelty movements. (Their "slaughter" also has biblical overtones).
  2. That we should approach the issue like an accountant, balancing costs and benefits.
  3. That the complete loss of bird-life would cause a plague of insects (this may be called the apocalyptic argument--with explicit biblical references).

 S.C. follows with this observation:

In order to make some estimate of their services, I lately observed a couple of sparrows who had young ones, and made twenty turns each per hour; and reckoning but twelve hours per day, let us compute what a number of those vermin were destroyed by that nest alone,
40 caterpillars per hour.
12 hours of feeding per day.
480 caterpillars destroyed per day.
7 Days supposed between hatching and flight.
3360 caterpillars destroyed by one nest alone in one week.

Here it is, the single most important calculation in the history of bird protection--the model of what would be called "economic ornithology," and a number that would be cited for the next 200 years. S.C. watches a single pair of sparrows for a single hour and then extrapolates, using figures that are admitted to be crude estimates, to get to the magic number: 3360 caterpillars destroyed by one nest in one week. By sparrows.

I don't have space here to cite every subsequent use of this number (while I was researching, I imagined an entire blog obsessively devoted to this project). Suffice it to say that "Bradley says a pair of house sparrows destroys 3360 caterpillars a week" became a common fact cited again and again in bird books and agricultural journals, and that this number directly contributed to the notion that house sparrows were the ideal solution to the problem of cut-worm infestation in the cities of the United States. [Buffon, in his influential natural histories, apparently cited the number, rounded up to 4000 (I've yet to solidify this link but it is very likely), Buffon was in turn cited in Bewick's very authoritative bird books, and the rest is history.]

This is not necessarily what S.C. intended. Rather, he was using a rhetorical gesture that would become the key approach used by economic ornithologists in spreading their wisdom, namely the assertion of the counter-intuitive scientifically-grounded fact. You may THINK that house sparrows are the most useless of useless birds, but IN FACT, if you OBSERVE CAREFULLY, you will find that EVEN SPARROWS have their uses when it comes to controlling insects. S.C. goes on to say that other birds (tom-tits, wrens, et al) are almost certainly MORE useful than sparrows in controlling caterpillars, but it was the sparrow number that stuck.

This is not to make light of the overall importance of S.C.'s letter (and Bradley's use of it). Bradley's correspondent goes on to detail several more cases of unfair prejudice against birds (tom-tits, bullfinches, and rooks in particular) and (anecdotal) evidence supporting the idea that bird extirpation (even of sparrows) leads to insect infestation. Most remarkably, S.C. proposes a law for bird preservation, protecting parent birds, nests, eggs, and young ones. Taking into account the possible objections of sportsmen, he proposes the closed season only during the breeding period (March to September).

Finally, it should be noted that Bradley includes an additional piece of business. He had shown S.C.'s letter to Charles Dubois, treasurer of the East India Company (and famous sponsor of Mark Catesby's expeditions).  Dubois approved and added that the destruction of moths by birds (or lighted candle) should be figured into the total number of caterpillars destroyed (at least 300 per each moth). 

[UPDATE: March 28, 2017]

I've found the Mortimer text referenced above. In Chapter III of his Treatise on Husbandry, he writes:
Bullfinches are most pernicious birds to young fruit trees, by feeding on the young pregnant buds in spring time which contain the blossoms and are the only hope of the succeeding year.  
If January prove very cold, that the blackthorns are backward in February, the bullfinches will be very busy in the garden. The trees there growing being forwarder than in the field in a cold winter. I have known so many of them in a garden, that in a little time they have almost totally unbudded the plum trees, currant trees, etc. of a whole town. They are easily taken off with a fowling piece, only you must be cautious that your shot spoil not your young layers or branches of your trees.This bird is so bold that no scarecrow or other thing will frighten him from the trees he delights to feed on; but on the Morocco plum or the Damson, he will settle and feed, notwithstanding all you can do: so that the best way to preserve these bugs is to birdlime the twigs.
Goldfinches are very injurious to the gooseberry buds, coming flights, and cleansing of a whole garden of them immediately, as the bullfinches will the bud of the currant trees: the remedies against them are the same with the other. 
The chaffinch, greenfinch, titmouse, and other small birds are injurious to some fruits, but not like those before-mentioned, who will prey upon the buds of all sorts of fruit trees, under the very nets that cover the trees and near unto the dead bodies that hang on them. 
Sparrows, although they are but small, yet are they a numerous generation of corn eaters: It is unknown how much they devour and what a great damage they are to the husbandman, especially in scarce and dear years. Many ways are made use to destroy them but none more effectual than the large folding sparrow net, which will take many dozens at a draught: they beings so easily induced to come to a shrap or place baited for them especially in hard weather in the winter, and in the summer before the corn is ready for them: at both times meat is scarce abroad, and then they flock to barns. To prevent birds eating of new sown corn, sow lime or soot upon it. 

Next: Richard Bradley and Claudius Aelianus

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