The Canadian Peregrine Foundation

Peregrine falcon adapting to urban lifestyle
Wednesday February 6th 2008

By Brian Unwin Last Updated: 1:01pm GMT 06/02/2008

The peregrine falcon is becoming a night hawk. The swiftest and deadliest of all avian predators is increasingly being seen soaring across city centre skylines and nesting in high rise blocks.

A peregrine falcon leaves its nest in New York And it has developed a different killing technique to go with its new urban lifestyle.

The falcon, famed for its 100mph stoop, is becoming nocturnal - using the glare from illuminated buildings to spot its prey - and the shadows they throw up as cover for its deadly ambush.

With tall buildings offering ideal nest sites and feral pigeon populations ensuring an ample food supply, there were clear advantages in the peregrine moving from the countryside to the city.

Floodlit buildings have provided new opportunities with night-flying birds and even bats now very much in the peregrine's sights.

"Evidence of nocturnal hunting behaviour illustrates just how well adapted peregrines are to the urban environment", says a report in the new edition of the journal British Birds.

Studies in France, Germany and Holland tell how they "use artificial light directed on to buildings at night to their advantage, attacking prey at short distances and using the shadows to avoid being dazzled while looking for a potential kill."

Investigations in Berlin and New York found that during the peak migration period of potential quarry species, peregrines were not seen to be hunting until after sunset.

In Taiwan, peregrines are known to use a tall bridge tower that is lit up at night. Filming of their nest site revealed that almost 80 per cent of 44 prey item recorded were brought in after dark.

A peregrine food cache on an industrial chimney in Holland consisted of hundreds of birds - mainly moorhens, water rails, teal (Europe's smallest duck) and snipe - stored for later feeding, the report adds.

"The site, illuminated at night, is on a main migration route for these species and it is thought that they were probably taken at night while on passage."

Direct observations from New York's 1,250ft high Empire State Building found peregrines "regularly hunting nocturnal migrants such as yellow-billed cuckoo and Baltimore oriole.

"The presence of at least three peregrines at any one time was significantly more likely on evenings when more than 50 migrants were counted passing over during the night."

Artificial lighting can cancel out the natural camouflage of prey species' plumage, explains the report by Edward Drewitt of Bristol's City Museum and Art Gallery, and Nick Dixon.

For instance waterbirds with dark upperparts and pale undersides are camouflaged from aerial predators while swimming - but not if flying at night in artificially illuminated areas.

"Under such conditions, pale underparts are strikingly obvious from below, while peregrines perched on high vantage points will see low-flying migrants as dark silhouettes against the illumination."

However, modern lighting in towns may have simply helped them develop night-hunting abilities they already had as the report also gives examples of prey being taken after dark in unlit wild locations.

For instance, off American north Pacific coasts, peregrines are known take seabirds such as fork-tailed storm-petrels, ancient murrelets and Cassin's auklets at night or during twilight.

They have also been recorded trying to catch bats at cliff sites in Northern Ireland. Radio-tracking of birds fitted with tiny transmitters has indicated flying and possibly hunting at night in Somerset.

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