Rook Corvus frugilegus

About this Pest

KEY CLUES

Distinctive features: Large glossy black crow-like bird with feathered thighs. Adults have pale bare skin around the base of the grey-black beak. Juvenile rooks lack the bare patch and have a narrower bill. Black legs and feet with sharp claws.

Size: Males up to 450 mm in length and 425 g. Females somewhat smaller.

Droppings: TBC

Footprints: Large passerine (perching bird) footprint, one long toe pointing backwards, three toes pointing forwards.

Kill signs: Holes pecked in eggs.

Vegetation damage: Pasture and newly sown seeds dug up; sprouted seeds pulled out.

Eye shine: Not applicable because diurnal (daytime) species.

Distribution: Largest populations on the east coast of the North Island from Hawke’s Bay south, with scattered sightings elsewhere. Nearly eradicated from the South Island.

WHY ARE ROOK PESTS?

Unwanted Organism

The rook is classified as an Unwanted Organism in New Zealand due to the potential adverse ecological and agricultural impacts this species can cause and are the focus of eradication campaigns by several regional councils. If you think you have seen a rook, phone the Ministry for Primary Industries Pests and Diseases Hotline 0800 80 99 66.

Ecological impacts

The ecological impacts of rooks in New Zealand have not been well-studied but they can be very territorial, driving other bird species away from their large communal groups (rookeries). They prey on introduced and native species, including small and ground nesting birds, lizards and invertebrates and eat birds’ eggs.

Other impacts

Rooks are an agricultural pest for several reasons. They feed on newly sown crops, particularly cereals, peas, maize and squash, often pulling recently germinated plants from the ground to get the seeds. They can also damage pasture by tearing it up when searching for grubs, which could result in paddocks having to be completely re-sown when large flocks of rooks are present. Rooks have also been known to damage silage by tearing holes in the plastic wrapping and to peck out and eat the eyes of living sheep and lambs that are immobile as a result of disease or restraint. Overseas rooks can also be a nuisance and risk to human health. They scavenge for food scraps in public places and at landfills, where they can become a hazard when present in large numbers. They will fly at and sometimes attack humans during breeding season and can carry and spread diseases such as listeria. Because rooks are persecuted/controlled in New Zealand they avoid humans and do not feed or associate near humans so this last impact is theoretical only.

Read more about rooks.

 


Droppings

Separate

We have been unable to find any specific information about rook droppings. We would be pleased to receive informatio.

Can be confused with:

Can be confused with the droppings of other bird species

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Footprints and Tracks

Paws and feet

Rooks feet are typical of perching birds, with one long toe pointing backwards and three toes pointing forwards. The toes all have sharp claws. Adult foot size is estimated in the range of 95 to 100 mm long, although there is little information available on this. If you can help with this clue, we would be pleased to hear from you > contact.

You are most likely to find footprints where rooks have been searching for seeds or grubs on pastures with damp bare soil.

Can be confused with:

Rook footprints can be confused with the footprints of other perching bird species of similar size. Magpies are the most similar in size and most likely to forage in similar places.

Dens and nests

Rooks can form large breeding colonies of several hundred birds, called rookeries, where (in New Zealand) they live from approximately August to mid-December. They generally build their rookeries in large isolated tall trees such as pine or eucalyptus. Both the rookeries and the nests are an easily recognised sign that rooks are present. The nest is typically a large untidy platform of twigs, lined internally with smaller twigs.

Can be confused with:

Rook nests could potentially be confused with nests of some shag species since they also nest communally in large trees. However, the fishy smell of a shag colony will distinguish it from that of a rookery and shags are more likely to nest close to waterbodies and the sea. Lone rook nests could be confused with those built by magpies which make nests in a similar way.

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Vegetation Damage

Understorey (less than 3m)

Rooks can pull up large clots of dirt when digging in grassland looking for grubs or seeds. Large bare patches in grassland with holes poked in to the ground may be caused by rooks (if these occur in your locality).

Can be confused with:

Other species that cause similar field damage include pūkeko pulling up seedlings; pigs furrowing; birds such as blackbirds, thrushes, magpies, seabirds and wading birds also sometime dig for invertebrates in fields. Weka can cause extensive ‘grubbing’ in pasture and kiwi also use their beaks to search for invertebrates and leave round holes. Unless sighted in the act, it is difficult to determine the particular species.

Fruits and Flowers

Rooks eat small amounts of fruit and have also been observed caching walnuts. If you find some nuts or seeds in a hole in the ground covered with grasses then you may have found a rook cache.

Can be confused with:

Rook damage to fruits and flowers can be confused with damage caused by other fruit and flower eaters, such as birds, possums and rats.

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Kill Sign

Fur, feathers or scales (vertebrate)

Birds

Rooks may eat nestlings of other bird species, especially small birds and ground-nesting birds. No information could be found to describe what rook predation looks like or how it differs from other predators.

Mammal

Rooks may also eat small mammals, such as mice and may feed on already dead larger mammals. No information could be found to describe what rook predation or mammal feeding sign looks like or how it differs from other predators. Small mammals, such as mice, are probably swallowed whole, so it is unlikely that evidence is left behind. 

Lizards and frogs

Rooks can eat lizards and frogs. Not much field sign will be found because these species would be swallowed whole.

Note: some regurgitated bones may be present in rook crop castings.

Can be confused with:

Predation of other predatory and omnivorous birds, including pellets that other bird species regurgitate. Beak pecking marks on animal remains killed by larger prey or carrion could be hard to attribute to a specific bird species. Mammal predation is usually different to that caused by birds. Remember, too, that animal remains might have been scavenged.

Insects or snails (invertebrate)

The most obvious sign of rooks feeding on invertebrates is the damage they can inflict on pasture when digging for grubs. See more on this under rook damage to vegetation understorey. Little information could be found on the remnants left behind after a rook has eaten invertebrates or snails. It is possible that, like other birds, rooks peck holes in snail shells to extract the snail. Other invertebrates are likely to be swallowed whole, so no field sign will be found.

Can be confused with:

Pasture damage caused by other bird species or pigs. Sign left by other birds is likely to be similar.

Eggs

Rooks will eat the eggs of other bird species, especially of small birds and ground-nesting birds, although little is documented about characteristic signs of the egg predation. Rooks probably peck a hole in the egg.

Can be confused with:

A number of bird species prey on eggs by pecking holes in the shell and eating the contents. Mammals such as rats, stoats and possums tend to push their snouts into an egg, so the broken fragments point inwards but these often remain partially attached to the shell (or shell membrane). Remember, too, that egg remains might have been scavenged.

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Other Clues

Sound

Rooks make a characteristic “caw’ or ‘kaah’ call, or occasionally a higher pitched ‘kiow’. These are given both in flight and while perched.

Can be confused with:

Rook calls could possibly be confused with those of sulphur-crested cockatoos where their distribution overlaps (sulphur-crested cockatoos occur in New Zealand on the west coast of the North Island, Banks Peninsula and the Catlins in the South Island) but will be distinctive elsewhere.

Body covering

Rooks have glossy black feathers with a purple or green sheen.

Can be confused with:

Tūī also have glossy black feathers with a purple or green sheen.  Rook feathers will mostly be larger than tūī feathers. A black feather found on pasture could belong to a variety of bird species. Reportedly people can confuse variable oystercatcher and flying black shags for a rook.

Distribution

In New Zealand, rooks are common on the east coast of the North Island from Hawke’s Bay south. They were common on Banks Peninsula but pest control has severely reduced their numbers there, and they may be completely eliminated from there.  There are reports of scattered colonies or single birds throughout New Zealand and juvenile and adult birds can disperse widely.

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MORE ABOUT ROOK

Origin

The rook was introduced to New Zealand from Europe several times during1862–74. Many introductions failed but liberations in Hawke’s Bay and Canterbury were successful.

Description

Rooks are a large glossy black crow-like bird with feathered thighs. They are the only crow-like bird in New Zealand (other than perhaps the kokako which was also known as the blue-wattled crow). The adult birds have pale bare skin around the base of a grey-black beak. Juvenile rooks lack the bare patch and have a narrower bill. The eyes are brown. The legs are black and the feet have sharp claws.

Size and weight

Length of up to 450 mm; the male can weight 425 g and the female 375 g.

Behaviour

Rooks are rarely solitary and mostly occur in large groups. Collective nouns for rooks include ‘building’, ‘parliament’, ‘clamour’ and ‘storytelling’. They can form large breeding colonies of several hundred birds, called rookeries, during the breeding season, which is generally August to November / mid-December in New Zealand. At other times adults and juveniles can congregate in large flocks of 10 to more than 100 birds.

Rooks usually lay three to four greenish-blue, brown-mottled eggs. The female incubates the eggs and broods the nestlings and the male feeds both the female and chicks. The fledgling period is about 33 to 38 days. Most rooks don’t start breeding until they are two or three years old. Rooks can live at least 11 years and a European bird has been reported as reaching 19 years of age.

Diet

Food is a mix of invertebrates and vegetation. The bird probes the ground with its strong bill for earthworms and insect larvae, and also digs up and eats recently sown cereal grains and legumes. Rooks eat small amounts of fruit, including nuts, small mammals, small birds and their eggs and young, and carrion.

Habitat

Rooks are usually found in rural/farmland areas but not in dense forest. Rooks use large trees, such as pine, macrocarpa and eucalyptus, to roost and nest but do most of their food foraging on the ground.

Can be confused with

Rooks can be confused with magpies and blackbirds but rooks are much larger than both. Magpies are somewhat similar in form but their patches of white or grey plumage distinguishes them the pure black rooks. Blackbirds are much smaller and, during breeding season, males have a yellow bill. Compare identifying features of rook, magpie and blackbird here.

In flight, rooks could be confused with black shags.

How to get rid of it

Regional Councils use helicopters to access rook nests and to lay poison. If you think you have rooks or know of a colony of rooks then contact your local Regional Council.


FIND MORE INFORMATION IN:

Porter, R.E.R. 2013 (updated 2016). Rook. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Waikato Regional Council. Retrieved (2017) from http://www.waikatoregion.govt.nz/Services/Regional-services/Plant-and-animal-pests/Animal-pests/rooks/
Heather B.D., and Robertson H.A. (1996). The field guide to the birds of New Zealand. Auckland, New Zealand, Viking, Penguin books Ltd.

Greater Wellington Regional Council. Have a Look for rooks. Retrieved (2017) from http://www.gw.govt.nz/have-a-look-for-rooks/