Monday, 27 March 2017

Woodpigeons calls and displays

Although the woodpigeon is the bird I come across most often and the one I record the most, it is still one of my favourite birds, the species that made me a birdwatcher. I find them truly stunning and very resourceful, feeling at ease in gardens, parks and woodland alike. Despite their reputation as grain guzzlers their diet includes leaves, nuts (acorns and beech mast), buds, flowers and berries, including rowan, ivy, holly, cotoneaster and alder, which they often reach with great acrobatics. Although Woodpigeons have featured often in this blog, here I am compiling and documenting their calls and displays, especially those related to reproductive behaviour. Although in his article on woodpigeon behaviour Cramp says that 'they mark their ownership of a territory primarily by just being there' as indeed 'a Woodpigeon perched in a tree bare of leaves is a large and conspicuous object' Woodpigeons have a simple, but interesting behavioural repertoire.

Advertisement call. A deep, repeated 5 note phrase that serves as a territorial song. This is the well know Woodpigeon song, often heard early in the morning.

Display flight. This is another territorial display most frequent in February and March. The male flies around the territory rising in a broad arc, and then gliding down with wings held stiffly horizontal advertising ownership. They can do the rising and falling a few times before alighting. Although mainly a visual advertising display, as the bird does not call, sometimes the bird will make a clapping noise with its wings at the apex of the arc.

The Bow display. It is a courtship display that territorial males perform when still unpaired and trying to attract a mate and also when the pair bond is becoming cemented. The male approaches the female and with the his neck is enlarged as he calls a 3 note call as he alternatively stretches its neck and then lowers its head, displaying the white and iridescent neck markings, and fanning the tail when it's highest. Check out this wonderful photo by Richard Hawley showing the display when fanning is at its maximum. Females can display some aggressiveness to the courting male, or move away or flee if they are not interested. This display often happens on trees, roofs or aerials, but occasionally on the ground. When on the ground the male will try and get closer and follow the female hopping to bow just in front of her.

Allopreening, billing and mating. Feeding the mate, gentle preening and billing precedes mating. I documented this behaviour in a series of photos here.

Slightly opened wings is a threat posture.
Fighting. Woodpigeons have very powerful chest muscles, which power their explosive take off and fast flight, and they also use their wings in territorial fights. Males will fly towards intruders landing in their territory and land adopting an aggressive stance, with neck stretched, flattened plumage and semi-open wings, and often this is enough to drive the intruder away. Occasionally, this develops into a fights, which sometimes occur in the depths of a tree. The pigeons will land near each other, alight their bodies and flap trying to hit each other (above).      
                                           
Nest calling. This is a call by the male signalling to his partner a suitable nest site. I've covered this on other posts (here and here) and it is described in detail in the article by Cramp cited below. The call is harsh, and guttural composed of two notes, here is a recording of the call. I want to share here a video I took this morning, in which I got a good angle. You can see pecking or nodding movements to the nest floor in between calls:




More information
Cramp, S. Territorial and other Behaviour of the Woodpigeon. Bird Study 5, 55–66 (1958). here.

Monday, 20 March 2017

A drop-catch game sequence

A caught a short clip of a young Herring Gull playing drop-catch today at a local nature reserve. The gull carried on for quite a while dropping and catching the item.

via GIPHY

Saturday, 18 March 2017

Moorhens mating

This week the local pair of Moorhens have been mating. Females in Moorhens and Coots, and presumably other rails, have a curious way of inviting their partners to mate: They bury their heads down into their chests.

Monday, 13 March 2017

Carrion crows dropping mussels

Today at Sewerby beach I was intrigued by a Carrion Crow, part of a large winter flock, appeared to drop something onto the rocks at the top of the beach, then come down to eat. Sometimes the crow would fail and repeat the action. The tide was low, exposing a flat platform of rocks with rich mussel beds, and the objects being dropped were actually mussels that the crows were collecting and carrying up the beach before dropping them on the solid rock to smash them (above).
Dropping potential food items to break them open has been previously documented, and best known in Golden Eagles (breaking open tortoises) and Lammergeiers (bones). Gulls and crows of various species have been recorded dropping intertidal hard-shelled molluscs hard substates, including roads. Intertidal foraging can be an important part of the diet of coastal crows in the winter, when insects are scarce. Crows will scavenge at the tide-line, or feed on small crabs, but some of these intertidal organisms, in particular periwinkles, cockles and mussels, are consumed after smashing them open by dropping onto hard substrates. Controlled observations of wild Carrion and Hooded crows show that crows chose larger mussels, more likely to smash and also providing more food. Shell dropping is not instinctive, young crows appear to perform rather poorly. They need to perfect their technique of dropping so that the height at which the mussels are dropped is the minimum height for them to break at impact, but not much lower. Young crows take more attempts at being successful.
There are three reasons why the minimum height should be used. One, dropping from higher up means wasting more energy flapping up. Also, higher drops means higher bounces and higher chances of the shell being lost. Finally, crows and gulls often steal from each other, a behaviour called kleptoparasitism.  Therefore researchers predicted that crows dropping mussels when other crows or gulls are nearby would be more wary of being robbed, indeed, crows with other crows or gulls nearby dropped their mussels from 2 m lower that lone crows.
Crow and gulls on mussel bed, the crow has already detached a mussel, while one of the gulls is still trying. Although many crows were actually busy either collecting mussels or breaking them up the beach today, I didn't see any gulls doing this.
Mussels are strongly attached to the rock and other mussels by threads, which can be hard to reach, as the mussels cover the rock very densely, not exposing the threads. It is quite a feat the crows manage to detach them
A view of the beach at low tide.

Despite the very bright light I managed a couple of clips here:


More information

Whiteley, J. D., Pritchard, J. S. & Slater, P. J. B. Strategies of mussel dropping by Carrion Crows Corvus c. corone. Bird Study 37, 12–17 (1990).

Davenport, J., O’Callaghan, M. J. A., Davenport, J. L. & Kelly, T. C. Mussel dropping by Carrion and Hooded crows: biomechanical and energetic considerations. J. Field Ornithol. 85, 196–205 (2014).

Berrow, S. D. , T. C. Kelly & A. A. Myers. The diet of coastal breeding Hooded Crows (Corvus corone cornix). Ecography 15, 337–346 (1992).