RICHARD WILLIAMSON Nature Trails...Peregrines plunder a very rich larder...

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So what is the cost of keeping our cathedral killers alive in Chichester each year? Not in money, but in birds they eat and which we might otherwise enjoy?

Research at three other urban sites in the UK (Bath, Bristol and Exeter) over a ten-year period show a surprising range of prey totalling 97 different species of birds and four different mammals.

The commonest birds taken in all three locations were feral pigeons. More than 1,000 at both Exeter and Bath which works out at one every three days at each place. I would say, having listened to what RSPB staff tell me, this would be par for Chichester. These are mainly town birds that breed in buildings, and foul the area, so are not missed much.

Second commonest with a quarter of those numbers are starlings. Again, the Chichester peregrines are seen to bring in lots of those from their breeding places to the southeast of the city, mainly the juveniles which are easily caught.

Next are redwings. These Scandinavian thrushes migrate here in great number some years. Forty thousand were seen passing Brighton in one day several years ago during a snowstorm. So most are taken during migration.

We then have a surprise for fourth favourite food item which are greenfinches. This would have been before the recent severe decline of these once common garden finches due to bacterial disease which wiped out half their number. I have not heard of any being brought to our cathedral.

Wood pigeons and collared doves are commonly killed and there are plenty of those to go around. Blackbirds are common prey, but with each pair able to have three broods each season that is not a serious threat to our favourite songster.

But I begin to feel like grumbling when snipe and woodcock come into the food chain. Until you find this is only three of each species per annum per pair. Nothing.

Neither does it matter when the odd rarity is claimed. A little auk would have been blown in and lost off the ocean. Wagtails, wrens, robins, dunnocks, skylarks and kingfishers were all taken in the southwest. But 28 magpies were eaten and 49 jackdaws.

Surprising prey included black-necked grebes and 18 little grebes. These migrate at night and it is well-known that peregrines hunt in the dark. That accounts for the noctule bat.

Another surprise was the grey squirrel and the four rats which the peregrines killed.

Released caged birds fuelled the mighty predators too, with canary, cockatiel, parakeet and 12 budgerigars giving extra strength to the urban raptors.

A total of 5,275 was catalogued at the three city sites and held not many surprises. For the Chichester peregrines the numbers and species seem compatible and are easily sustainable in the very rich larder this family control for themselves from their pinnacle above the woods and harbours.