Land of op­por­tu­nity

The much-loved Barn Owl is a skilled hunter when it comes to search­ing for food in the coun­try­side – but its suc­cess in se­cur­ing a meal de­pends on how land is farmed

Bird Watching (UK) - - Contents - WORDS: MAT BING­HAM

How the farm­ing of our coun­try­side can have a huge im­pact on Barn Owl sur­vival

ONE OF MY ear­li­est mem­o­ries was of my Dad and I driv­ing home in the win­ter. We rounded a bend on a lonely fen­land road in Dad’s old van and were greeted by an ap­pari­tion, a white ghost, a Barn Owl hov­er­ing above the grass verge. I was eight years old and can still re­mem­ber it clearly. White feath­ers with mot­tled fawn up­per edges and those haunt­ing eyes. Of the five species of owl in the UK, the Barn Owl is prob­a­bly the eas­i­est to see – the best time be­ing on a warm sum­mer evening dur­ing still con­di­tions.

In my ex­pe­ri­ence, Barn Owls nor­mally fol­low the same hunt­ing pat­tern each night, mov­ing fur­ther away from their roost or nest site un­til they make a suc­cess­ful kill. They tend to take the prey to a favoured perch to de­vour it whole or, if they have young, back to the nest. In the breed­ing sea­son, most of the hunt­ing is car­ried out by the male. He will bring food for the chicks and his mate while she is at the nest. I’m for­tu­nate in that, for sev­eral years, I’ve been able to watch two pairs of Barn Owls. One pair live near my home in the Mid­lands, which I call the Ash Tree Pair, and the sec­ond pair live in East Anglia where I grew up – I call them the Fen­land Pair. The Ash Tree Pair roost in one of four Ash trees, the rem­nants of an old hedge line. They select one of these trees to nest in each year. All four trees are suit­able for Barn Owl nest­ing but they have com­pe­ti­tion from Tawny Owls and Kestrels, who also use the trees. The Fen­land Pair nest in the eaves of an old barn that is used to store farm ma­chin­ery. Out­side of the breed­ing sea­son the male roosts in the barn on his own. I am not sure where the fe­male goes as there are very few trees in the area. She prob­a­bly roosts in an old agri­cul­tural build­ing some­where close by. The Ash Tree Pair’s hunt­ing ter­ri­tory is smaller than that of the Fen­land Pair’s, be­cause food is much more abun­dant, so they don’t need such a large ter­ri­tory. The Ash trees are sur­rounded by hay meadow, which the farmer cuts in late Au­gust to give the Barn Owls ev­ery op­por­tu­nity to find food for their young. Large ar­eas of scrub, a buf­fer zone, are left at the edges of the fields to en­cour­age wildlife and pro­vide cover for Brown Hares. In con­trast, the Fen­land Pair have a much larger ter­ri­tory, cov­er­ing sev­eral square miles. In the fens, hedges have been pulled out to

cre­ate large fields to max­imise agri­cul­tural pro­duc­tion. Less cover means fewer Field Voles, their main prey item. As a con­se­quence, the Fen­land Pair spend con­sid­er­ably longer hunt­ing, each night. There is, how­ever, a small area of scrub, per­haps an acre in size, next to the barn, and the Fen­land Pair al­ways start their hunt­ing trips by quar­ter­ing this field. I sus­pect this small area of scrub is why the barn was cho­sen by these owls. I have only ever seen the Ash Tree Pair hunt­ing in good weather and on clear, still nights. Con­versely, I have seen the Fen­land Pair hunt­ing in gales and driv­ing rain at mid­day. Hunger will drive Barn Owls to hunt at any time of day and in any weather. The Ash Tree Pair gen­er­ally fo­cus their hunt­ing in the sum­mer months in the hay mead­ows. Nor­mally, it only takes a few min­utes to catch a vole. The Fen­land Pair, though, can be away from the nest for long pe­ri­ods of time try­ing to find enough food to raise their fam­ily.

Us­ing senses to the full

Barn Owls hunt us­ing sight and sound and are per­fectly adapted to make best use of these senses. Their vi­sion is much more acute than ours; they can spot tiny voles in long grass and can prob­a­bly see urine trails made by the ro­dents. Barn Owls’ eyes are ac­tu­ally tubu­lar in shape, which pro­vides a greater dis­tance be­tween the front lens and the rear of the eye. This has the same ef­fect as a tele­photo lens, mak­ing it eas­ier to spot small ro­dents by mag­ni­fy­ing the im­age from fur­ther away. Their eyes are so large they can­not move them in their eye sock­ets, so they have to move their heads if they want to look some­where, other than im­me­di­ately in front of them. Owls com­pen­sate for this lack of eye move­ment by hav­ing a greater num­ber of neck bones,

al­low­ing the head to swivel as much as 280°. I have car­ried out ex­per­i­ments with the Ash Tree Pair by leav­ing dead mice in the hay meadow for them to feed on, but they com­pletely ig­nore them. This is be­cause their vi­sion is based on move­ment – voles are safe if they stay still. Barn Owls, like other owls, bob their heads, to help to gauge dis­tance when look­ing for prey. This be­hav­iour can also be ob­served in two other birds that hunt or find food un­der­wa­ter, the King­fisher and the Dip­per. The Barn Owl’s heart-shaped head is a func­tion of how evo­lu­tion has adapted its hear­ing. The shape of the face acts like a radar dish cap­tur­ing sounds and fun­nelling it to the ears, which are hid­den un­der the fa­cial disk feath­ers. One of their ears is set fur­ther back in the head than the other. It is thought that the pur­pose of this is to en­able the owl to bet­ter gauge dis­tance to prey by dif­fer­en­ti­at­ing how quickly the sound reaches each ear. Un­like most other birds, Barn Owls fly silently. This en­sures that their prey is not alerted to their pres­ence. Fly­ing silently also en­ables Barn Owls to hear move­ment from be­low with­out the sounds be­ing masked by the owl’s own wing­beats. Silent flight is achieved by hav­ing wing feath­ers that are frayed at the edges, which cre­ate less fric­tion with the air, and also the downy plumage helps to dampen noise. The feath­ers are more flex­i­ble than those found on other birds, but the dis­ad­van­tage is that they are not wa­ter­proof. Their leisurely, slow flight is ide­ally suited for scan­ning the ground be­low. Once a vole is spot­ted, the owl spills the air from its wings and drops onto it from above. The talons make sure the prey is im­mo­bilised be­fore the owl dis­patches it with a bite to the neck. Like other birds of prey, adult Barn Owls swal­low their prey whole and later re­gur­gi­tate a pellet con­tain­ing the in­di­gestible parts (fur and bones). From ex­am­in­ing the pel­lets of both the Ash Tree Pair and the Fen­land Pair, both pairs eat pre­dom­i­nantly Field Voles. The pel­lets are easy to spot un­der pre­ferred perches. The Ash Tree Pair tend to sit in one of the ash trees to di­gest their meal. The Fen­land Pair pre­fer to perch on the top of the barn. It can take be­tween six and 12 hours af­ter eat­ing be­fore a pellet is re­gur­gi­tated. Nor­mally a pellet can con­tain the re­mains of more than one prey item.

Barn Owls have up to five chicks in a brood and can have more than one brood in a year if the weather is good. The fe­male lays her eggs over sev­eral weeks and they hatch in the or­der they were laid. The re­sult is that the chicks vary in size. If the adult birds strug­gle to find enough food, it can be­come a fight for sur­vival and the chicks may be­come can­ni­bal­is­tic. The life ex­pectancy for a Barn Owl in the wild is about four years, al­though the mor­tal­ity rate is high. Col­li­sions with cars have a sig­nif­i­cant im­pact on owl num­bers, es­pe­cially in the breed­ing sea­son, and the loss of ei­ther bird if they have young, can re­sult in the chicks starv­ing. Dur­ing 2016, the Ash Tree Pair had a suc­cess­ful breed­ing sea­son rear­ing their young. How­ever, the Fen­land Pair were less for­tu­nate, as the barn they use was un­in­ten­tion­ally dis­turbed dur­ing the sum­mer months by farm work­ers, caus­ing the pair to aban­don the nest site. I am not sure if they had ac­tu­ally started nest­ing be­fore­hand. Maybe the pair will try to nest in the barn this year. The suc­cess of breed­ing is di­rectly re­lated to the abun­dance of prey and lack of dis­tur­bance, and farm­ers can have a sig­nif­i­cant in­flu­ence on both of these.

The Barn Owl’s feath­ers are mod­i­fied for silent fly­ing

A clas­sic Barn Owl barn

Barn Owls are not above perch­ing in trees, even among the cover of Ivy

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