Science: How falcons stomach the chase - New research into birds of prey separates the fast movers from the browsers. It's a question of guts. Malcolm Smith reports

If it's live entertainment you are after in the scorching midday of a Majorcan summer, it is hard to beat Eleonora's falcons. These small Mediterranean birds of prey - cousins of the peregrine - dive and twist in the air, accelerating after swifts and swallows, tumbling on to more sluggish moths, in a display of enormous agility. All to catch a lunchtime meal.

Falcons are high-speed chase and attack merchants. Not for them the easy gorging on a roadside rabbit corpse which can content a buzzard for hours. Or the lazy loafing on refuse tips, searching for meat scraps, which can keep a black kite's body and soul together day after day.

In order to feed themselves, birds of prey have evolved in a variety of ways. It is not all down to characteristics such as wing design and body shape. The efficiency of their digestion also, it seems, plays a major role, differing substantially between attackers, such as the falcons and sparrowhawk, and searchers, such as buzzards and kites.

New research, by Nigel Barton and David Houston of Glasgow University's Applied Ornithology Unit, has overturned the view that all birds of prey - because almost all of them are meat eaters - have roughly similar digestive efficiencies.

Drs Barton and Houston used feeding trials to compare the digestive efficiency of a peregrine, a specialist, attacking hunter, with that of a buzzard, a generalist, searching hunter. Both were fed two diets: pigeon, which is fat-rich and therefore provides a lot of energy, and rabbit, which has little fat (but more protein) and provides less energy.

The buzzards blossomed on both diets, maintaining their body weight. But the peregrines thrived only on the pigeon diet. With less energy-rich rabbit, peregrines lost more than 5 per cent of their body weight during the eight-day trial. Eventually, they might not have survived.

Their relative digestive efficiency (calculated by weighing food in and faeces out) proved different. Of 10 species of birds of prey examined, peregrines, at around 75 per cent, had the lowest digestive efficiency while buzzards, at up to 82 per cent, had the highest.

Other searching hunters, such as red kite and tawny owl, had a digestive efficiency as high as the buzzards. Tawny owls feed on a range of prey including small mammals, birds, reptiles and invertebrates. Like buzzards, they tend to stand around, perched on a post or branch, then drop on to their prey from above. Stealth and opportunism are their hallmarks.

More akin to the speedy peregrine, the woodland and garden-flying sparrowhawk catches much of its prey - small birds - in fast chases. The barn owl, though slower, also hunts on the wing rather than from a perch. The digestive efficiency of both sparrowhawk and barn owl is at the low end of the range.

These differences in bowel function are the result of varying lengths of small intestine. Drs Barton and Houston found that the small intestine of a typical searcher such as the red kite (never known for its agility and speed) was around 130cm long. The small intestine of the female peregrine, on the other hand, is some 95cm, while in the smaller males it could be as short as 72cm.

Assuming that, length for length, small intestines in different birds of prey are equally efficient at absorbing nutrients from food, then digestive efficiency is greater in those species with the most guts, at least anatomically if not behaviourally.

But why do the faster fliers have the shortest guts and therefore the least ability to extract goodness from their food?

It is all down to specialisation, say Drs Barton and Houston. Active chasers such as peregrines and sparrowhawks feed on birds. The success of an attack depends partly on surprise, but mainly on speed and agility. Although prey is abundant, several small birds need to be caught each day to fuel this energy-sapping behaviour. They need to consume up to a quarter of their body weight each day in food.

Presumably, such speed merchants have a small gut and a rapid throughput of digested food so that they can return quickly to their optimal flying weight after a meal. An overweight peregrine, merlin or sparrowhawk would never succeed in the chase. It is a question of trade-offs. For fast fliers, ability to capture prey is more important than squeezing every bit of goodness out of it after it is eaten.

The more easy-come, easy-go birds of prey such as buzzards and kites need to eat less than one-tenth of their bodyweight in prey each day. And they don't even catch all of this. Carrion eating is a speciality.

Such birds of prey have no weight problems to worry about. They digest more of their food more slowly, allowing them to make the most of a wide range of prey of much more variable nutritional quality.

Falconers seem to know all this already. The comparative food value of meat from birds and mammals and the benefits of feeding different falconry birds different prey is something determined by trial and error - and falconers have had plenty of time to work it out.

As a sport falconry probably originated in the Far East, perhaps as many as 4,000 years ago, but the first indisputable written evidence of falconry is from Japan in AD244. Widely practised in Britain before the Norman Conquest (the Bayeux tapestry depicts soldiers carrying hawks), falconry flourished in the Middle Ages.

Falconers may long have known what to feed a peregrine to optimise its breathtaking displays of speed. But little did they realise that those gut-wrenching dives are the result of especially speedy digestion.

(Photographs omitted)

Suggested Topics
PROMOTED VIDEO
News
ebooksAn evocation of the conflict through the eyes of those who lived through it
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

AIFMD Business Analyst / Consultant - Investment Management

£450 - £600 per day: Harrington Starr: AIFMD Business Analyst / Consultant - I...

Business Analyst Solvency II SME (Pillar 1, 2 & 3) Insurance

£450 - £600 per day: Harrington Starr: Business Analyst Solvency II SME (Pilla...

Manager - SAS - Data Warehouse - Banking

£350 - £365 per day: Orgtel: Manager, SAS, Data Warehouse, Banking, Bristol - ...

Web Analyst – Permanent – West Sussex – Up to £43k

£35000 - £43000 Per Annum plus excellent benefits: Clearwater People Solutions...

Day In a Page

Ferguson: In the heartlands of America, a descent into madness

A descent into madness in America's heartlands

David Usborne arrived in Ferguson, Missouri to be greeted by a scene more redolent of Gaza and Afghanistan
BBC’s filming of raid at Sir Cliff’s home ‘may be result of corruption’

BBC faces corruption allegation over its Sir Cliff police raid coverage

Reporter’s relationship with police under scrutiny as DG is summoned by MPs to explain extensive live broadcast of swoop on singer’s home
Lauded therapist Harley Mille still in limbo as battle to stay in Britain drags on

Lauded therapist still in limbo as battle to stay in Britain drags on

Australian Harley Miller is as frustrated by court delays as she is with the idiosyncrasies of immigration law
Lewis Fry Richardson's weather forecasts changed the world. But could his predictions of war do the same?

Lewis Fry Richardson's weather forecasts changed the world...

But could his predictions of war do the same?
Kate Bush asks fans not to take photos at her London gigs: 'I want to have contact with the audience, not iPhones'

'I want to have contact with the audience, not iPhones'

Kate Bush asks fans not to take photos at her London gigs
Under-35s have rated gardening in their top five favourite leisure activities, but why?

Young at hort

Under-35s have rated gardening in their top five favourite leisure activities. But why are so many people are swapping sweaty clubs for leafy shrubs?
Tim Vine, winner of the Funniest Joke of the Fringe award: 'making a quip as funny as possible is an art'

Beyond a joke

Tim Vine, winner of the Funniest Joke of the Fringe award, has nigh-on 200 in his act. So how are they conceived?
The late Peter O'Toole shines in 'Katherine of Alexandria' despite illness

The late Peter O'Toole shines in 'Katherine of Alexandria' despite illness

Sadly though, the Lawrence of Arabia star is not around to lend his own critique
Wicken Fen in Cambridgeshire: The joy of camping in a wetland nature reserve and sleeping under the stars

A wild night out

Wicken Fen in Cambridgeshire offers a rare chance to camp in a wetland nature reserve
Comic Sans for Cancer exhibition: It’s the font that’s openly ridiculed for its jaunty style, but figures of fun have their fans

Comic Sans for Cancer exhibition

It’s the font that’s openly ridiculed for its jaunty style, but figures of fun have their fans
Besiktas vs Arsenal: Five things we learnt from the Champions League first-leg tie

Besiktas vs Arsenal

Five things we learnt from the Champions League first-leg tie
Rory McIlroy a smash hit on the US talk show circuit

Rory McIlroy a smash hit on the US talk show circuit

As the Northern Irishman prepares for the Barclays, he finds time to appear on TV in the States, where he’s now such a global superstar that he needs no introduction
Boy racer Max Verstappen stays relaxed over step up to Formula One

Boy racer Max Verstappen stays relaxed over step up to F1

The 16-year-old will become the sport’s youngest-ever driver when he makes his debut for Toro Rosso next season
Fear brings the enemies of Isis together at last

Fear brings the enemies of Isis together at last

But belated attempts to unite will be to no avail if the Sunni caliphate remains strong in Syria, says Patrick Cockburn
Charlie Gilmour: 'I wondered if I would end up killing myself in jail'

Charlie Gilmour: 'I wondered if I'd end up killing myself in jail'

Following last week's report on prison suicides, the former inmate asks how much progress we have made in the 50 years since the abolition of capital punishment