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.
Monday, 20 March 2017
Saturday, 18 March 2017
Monday, 13 March 2017
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.
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).
Sunday, 29 January 2017
I then remembered a line of five fishing female Goosanders last year in a Swiss lake, swimming and diving in an orderly line along the shallows. They were behaving as if they were fishing cooperatively: by rounding up fish they would increase each of the individuals success rate. This cooperative fishing has also been observed in Cormorants and in the close relative of the Goosander, the Red-breasted Merganser.
The five female Goosanders fishing in a line, the individual at the far end peers under the water.
Des Lauriers, J. R., & Brattstrom, B. H. (1965) Cooperative feeding behavior in Red-breasted Mergansers. The Auk, 639-639.
Saturday, 28 January 2017
I have anecdotally documented play in gulls since Ralph Hancock drew my attention to this behaviour in his blog. Play has been described in gulls before, but only solitary play. But, was the behaviour I watched social object play? According to Judy Diamond and Alan Bond, in a review on social play in birds (where gulls are not mentioned) state:
'Social object play occurs when two or more individuals engage in repeated interaction with one or more inanimate objects in the environment without subsequent consummatory behavior. The best evidence of social object play is provided by contests over items that cannot be otherwise turned to useful purposes. Role reversals are common in social object play, and the interaction often ends with the contested item simply being discarded.'I believe that the sequence I watched fits this description quite well. The gulls respond to one another in which the 'carrier' changes direction to avoid the 'chaser' and the chaser follows the carrier paying attention to what it does and is quick to retrieve the object when dropped. The interaction ends when the item is discarded. The interest in the moss by the second individual is affected by the carriers interest in it, like the object is given a new meaning as a 'toy'. Much evidence on social play in birds is anecdotal, which a few exceptions, notably in Keas and Ravens. However, given how social gulls are, and how opportunistic, with much adult behaviour involving stealing food items from each other, it appears surprising social play hasn't described in gulls. Possibly casual watchers of distant gulls assume food objects being the centre of attention instead of inedible 'toys'. The park's wintering flock is well used to people and allow close approximation, so it is easy to check what the gulls are handling. I should definitely pay more attention in the future to potential play sequences.
For more posts at The Rattling Crow on play in birds click here.
Diamond, J., & Bond, A. B. (2003). A comparative analysis of social play in birds. Behaviour, 140(8), 1091-1115.