Grey Crows, Black swifts' Nests Raiders

Foraging behaviour

Type of animal

Corvus cornix (Hooded Crow)

The head, throat, wings, tail and thigh feathers are black and glossy, the plumage is ash-grey.

Habitat and foraging area

The overflown land along the River Desna, Bryansk Region, Central Russia, Eastern Europe

Diet

a constant scavenger – insects, molluscs, low-water small fish, eggs and small chicks

Who it is foraging with

other conspecifics

As observed, usually the crows are wandering along the river bank in low water in the group of 2 – 5 species, 1 starts its foraging tactics while the rest continue wandering about

Time of the year, season

Late spring (May) – summer (July, August)

Mornings and evenings

No human disturbance

Observation time

10-30 min daily

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During our regular daily walks with my dog Rey while staying on the sandy river bank I observed in one particular place a group of several crows, from 2 – 5 species, wandering in the low water foraging for water insects and small fish.

The other side of the river is cliffy, about 3 meter high, on the whole length of it there are black swifts’ nests (burrows). A couple of meters away from the cliffy bank’s edge there is a high-voltage network, to which the crows fly from time to time to sit on the wires.

I was curious if their behaviour – the repetition of actions: foraging in low waters, then flying to the high position – has something to do with the black swifts.

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It is known that crows can feed on eggs and chicks of black swifts ruining their nests in the cliffs.

My observation made me guess if their actions - foraging in low waters opposite the black swifts’ nests location then flying to high posts from which the black swifts’ nests can be well observed  - are a foraging strategy: observation and waiting tactics, side-tracking attention.

If the crows attack the nests all of a sudden without the side-tracking attention tactics the black swifts are quick in starting harassing them by mobbing.

As I observed especially during their nesting time a couple of black swifts were always on the alert acting like guards to inform others about the possible danger and also to warm the animals and people who appear close to their nests that they see them and trying to drive them away.

I saw this tactics on myself and my dog – as soon as we appeared on the bank opposite the cliff a couple of black swifts  started flying over my head and over my dog chirping and they flew away only when we starting moving off the bank.

Thus, the crows should use some strategy which can allow them to side-track the attention of the black swifts or they should always observe the nests waiting for grown-up black swifts to fly away for some time – for example, for food foraging, for them to ruin their nests.

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I have been doing regular observation on a daily basis, in the same place, in the evening and morning time.

I use the watch to see if the crows repeat their strategy regularly.

Possible confounds can be: weather conditions (rain, heat), human disturbance.

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Thus,

1. In foraging for black swifts’ eggs and chicks the crows use the following strategy:

-          Observation from different places and angles

-          Side-tracking attention: walking in low waters,climbing the cliff as if pecking insects in the grass , not in a straightforward manner but in circles until they reach the nests as if they didn’t intend to do it – “I was walking and suddenly I saw it”.

-          One works, the rest make a crowd diverting attention: usually 1 crow moves to the nests while the rest of the group stay below continuing doing their things as if nothing is happening.

2. As soon as the crow is near the nest it acts quickly in checking the nest. In case black swifts are quick to notice it and start mobbing the crow flies away, then returns to the group. One foraging act takes about 10 min, so they can repeat these raids regularly every 10 min.
3. There is a difference in how quickly the crows can come to the nests on which the success of their foraging can depend: if the crow flows to the nest straightforward it is sooner to be harassed away by mobbing black swifts than if it moves to the nest stealthily.
4. The crow can use the time when black swifts fly away from the nests for food foraging.
5. There is a difference in how successful the crows can be depending on the season: during the nesting time the black swifts seem to be more on alert and do mobbing in large numbers than at the time of fledgelings when the young birds are away from the nests practicing flying and there is nothing in the nests for the crows and fewer black swifts take part in mobbing.