Rooks hoarding acorns

It is a mast year, with a bumper crop of acorns across the city. October is peak acorn season and last week I saw the first Rooks carrying acorns. Acorns are packed with energy, and several bird species take advantage of them. Woodpigeons, presumably swallow them whole from the trees, but Rooks and Jays collect the harvest and store it for use during the winter. Both species are scatter hoarders, and cache individual acorns on the ground, and use their extraordinary spatial memory to recover them later in the year, when other food resources are scarce. Although the Jays are best known for this behaviour, Rooks are also amazing acorn hoarders. Rooks can transport acorns - and other food items - in a pouch under their tongue, which obviously bulges as they fly over with their pouch full. The number of acorns they can carry depends on the acorn size, and varies from 2 to 7. They prefer to cache the acorns on grass, and can fly up to 4 km from oaks to suitable grassland. Once they find a good spot, they drop all the acorns they are carrying and bury each one by one, by first making a hole in the ground with their bills, and then hammering the acorn in and covering it with grass, leaves or soil. Later on, they will visit the caching sites in the winter, find their stored acorns and crack them open to feed. 

A vocal Rook on an oak canopy, surrounded by plenty of acorns.

Rooks, unlike Jays, are very social and engage in communal acorn collecting, becoming very vocal when landing on the oaks canopy. They prefer to gather acorns with other Rooks, and individuals appear to join other individuals gathering acorns by flying in the opposite direction of individuals with full bills. When it comes to caching though, Rooks prefer to be alone, to avoid cleptoparasism, when other individuals try and steal their stored acorns.

Rooks displaying, the individual on the right, with distended sublingual pouch, passed an acorn to one on the left, presumably they are a mated pair.

More information

Waite, D. R. K. Food caching and recovery by farmland corvids. Bird Study 32, 45–49 (1985)

Källander, H., 2007. Food hoarding and use of stored food by rooks Corvus frugilegus. Bird Study, 54(2), pp.192-198.

Rook picnic

People were not the only ones enjoying the sunny and warm Sunday. A Rook walked around the picnic tables, intently looking around and underneath in search of scraps. A few people threw scraps to the rook and she filled her gular pouch with the tidbits. Its fledgling, precariously perched on a nearby tree, called. The Rook went back and forth taking food to its offspring.

Fledglings galore

The resident birds seem to have synchronised their breeding to such extent that I saw/heard seven different species of fledglings or chicks in my way to work. A Blackbird (#1) fledgling gave a try to hunt for itself, its parents out of sight. It was hilarious to watch it picking up a dried berry and dropping it and listening for worms.

A lovely fluffy Robin (#2) fledgling by the university parking lot, still very naive, let me get quite close (top photo), a pair of Greenfinches landed next to it and had me confused for a while!

Then a pair of noisy rook (#3) youngsters by the university woodland area demanded to be fed, I could only get a poor shot.

The family of Wrens (#4) I pictured a couple of posts ago were still around, the young giving their calls from a bed of nettles and docks opposite the Wilberforce building.

In my way back from work, a lovely family of Long Tailed Tits (#5) 'see-see-seeing', but the young ones shun me and only gave me their tails to photograph.

In my kids school, the Blue Tit (#6) eggs have finally hatched and I watched the live footage, with one of the parents sitting on very hungry and bare chicks

Near home, the Starling (#7) adults and youngsters in the nest have starting calling to each other with their 'churrr' calls which mean that they are almost ready to leave their nests.

Beach Rooks

The last couple of times I've been at Hornsea beach I've been surprised by the gang - sounds more appropriate than the collective names of "building" or "clamor" - of rooks. They feel at ease cruising the beach up or down on the sand, gliding over the waves or over the promenade wall in search of morsels of food. They look like rooks that tried to be a seagull and they quite liked it. I love how incongruous they look with the blue backdrop of the sea, but also how the behaviour of this particular group of individuals illustrate how resourceful corvids are.

Nesting Rooks

Rooks are not common birds in the city, they suddenly appear when houses make way for the first grassy fields in the outskirts. Somewhat surprisingly there is a small rookery in the university grounds. Probably the large mature trees attract them. They are not present year round though. I heard a group in January and I hadn't heard them again until today. Suddenly, they have taken over the place having decided that it is nesting time. Their constant, excited drawn out single 'kaah' calls - quite different from the repeated, harder and sharper calls of the Carrion Crow - filled the air. There were at least five evident nests in construction - all of previous years nests all fell out with storms and high winds - , one just a little jumble of sticks. Rooks break off twigs and branches from trees instead of collecting nest materials from the ground, and they were coming and going from their nests to a nearby Alder where they broke off twigs for their nest. It has been suggested that collecting branches from living trees allow for better size and strength selection This description taken from Bayne, 1929 was very fitting today, with squabbles at some nests possibly as a neighbour tried to steal a precious stick.

"Most birds do their nest-building quietly and as secretly as possible. But the rooks cannot hide theirs, so they talk about them freely. Every time they come back with a twig they shout the news to the whole rookery and to any one else who may be able to understand them. But it is dangerous for them to boast too much about a stick, for it may be stolen by a neighbour when they are gone to fetch another." 

This series of photos taken on a few minutes illustrates the activity in the colony.

A Rook leaves its nest calling

This three Rooks were collecting sticks atop an Alder. The bird on the right has already got its stick.

This bird spend a good few minutes wandering aroung the tree undecided and left with nothing.

Bird returning with a branch

For this one a little twig will do