Carrion Crow, Regurgitated.

This morning there was a lone carrion crow in the garden. Nothing unusual about that, though to be truthful although carrion crows are common around here, as elsewhere, rarely does one come into the garden and perch on the fence. 

Julie my wife alerted me to its presence surveying the garden.  It was one of those autumnal days when everything is sodden. Not quite freezing overnight but a heavy dew covered every available surface as the mist began dispersing with the strengthening sun. Earlier I'd seen the flash of a male sparrowhawk over the garden, though I was preoccupied in other things to concentrate on garden activity. The carrion crow however grabbed my attention, crows being an interest to me. I readily forget how large these corvids are when seen close too. Much like herring gulls when in the garden, who seem to fill it with their wingspan, this crow dominated the fence. That heavy black bill directing the observant deep set eyes to survey the scene, a crow seemingly at rest. 

Though highly intelligent carrion crows (Corvus corone) are the most wary of the corvids in my experience, never letting me get close to them. This year a pair successfully raised two (possibly three, but I'm unsure) young in the trees about 100m away. Squabbling magpies mobbing the crows each time they flew into the tree alerted me to the nest back in the spring. That squabbling was to continue all summer and well into September. The adult crows used the large fir tree in our garden as respite from this bickering it seemed, but they never came into the garden. Either one or both would sit on the top most branches preening and generally observing the world, before suffering the magpies wrath as they returned to the nest. Interestingly a pair of magpies had a nest in the fir tree this year, tit for tat maybe?

Whether the bird I observed preening its wing was one of the same adults I'm unsure, though logic decrees it would be and in its territory.  After a few minutes watching this crow it hopped off the fence and down onto the gravel. There on the path it flicked over a few stones before flying up onto the shed roof. Slipping and sliding down the shed roof, the crow then hopped onto the back wall and stood for a while. A perfect poised motionless corvid. I was tempted to get my camera but knew it would have disappeared before I returned. I therefore watched. 

It was while simply observing I saw the crow open it's bill and almost as if silently craa-ing, shook it's head while keeping its bill wide open. Again the bill opened, this time turning its head in the opposite direction. It then hopped slightly to the left and opened its bill once more, this time a pellet fell out of the crow onto the wall. I've known for years that crows regurgitate pellets but I've never seen this actually happen (nor have I been absolutely sure I've found one in the countryside). It is well known that birds of prey, especially owls regurgitate indigestible food remains, but a number of other bird species regurgitate too including herons, and dabbling ducks. And also crows; thanks to the work a century ago by Sven August Heintz a Swedish biologist. Post pellet regurgitating I read a paper reviewing his work [Green et al 2019].

In this recent article by Green et al they review the work of Heintz in the context of contemporary science and ornithology. A century ago Heintz suggested at least eleven corvid species were key seed dispersal species both through cache, hoarding, faecal droppings and pellet regurgitations. One of the species confirmed as doing this was the hooded crow (Corvus cornix), which in 1917 was then considered the same species as the carrion crow, with the former just more plentiful in numbers in Sweden.   

Heintz stated that "It is well-known that some members of the crow family (Corvidae) are important for seed dispersal either via frugivory (e.g., when feeding on berries) or by scatter hoarding (e.g., of nuts).....corvids are partly granivorous and have long had a reputation for causing damage to cereal crops"

[Heintz] "... carried out germination experiments of the contents of regurgitated pellets and excrements from Magpie and Hooded Crow. Most germination trials were carried out in early spring, of seeds that had been collected the preceding autumn or winter. Although many seeds germinated within a few weeks, trials were run throughout summer and autumn..... in total Heintze identified 157 plant taxa from 42 families which were dispersed by corvids by endozoochory (dispersal via ingestion)

Heintz concluded “It appears that within these zoogeographic areas [the Holarctic and the Neoboreal] corvids are the most important seed dispersers among all landbirds.” 

All of the above I gleaned from reading Green et al after watching the crow on my garden wall. Which after regurgitating its pellet flew off, allowing me to collect it (image above).

At the time of writing I have not dissected the pellet though on external examination it is packed with what will be indigestible seed husks and what look like acorn remains. Which was interesting in itself, as the literature suggests most regurgitations occur when crows feed on beetles and other invertebrates with tough carapace or wings. A quick search on the internet drew a blank for grain derived pellets. Could it be that seed based pellets are less obvious as they fall apart and are dispersed by wind more readily?  More investigation needed I feel, although given corvids are very granivorous during harvests and in autumn, it is not surprising really what this pellet contains.

That simple act of watching a carrion crow in the morning opened me up to the work of Heintz which until today I'd not known about. I'm not alone it seems. A quick scan through indexes in various books I have on crows fail to mention Heintz, seemingly Green et al are correct in their own conclusion that the work of that Swedish scientist a century ago has largely been forgotten, but it stands the test of time and is as pertinent today as in 1917. 

Reference :

Green, Andy J, Elmberg, Johan and Lovas-Kiss, Ádám (2019). Beyond Scatter-Hoarding and Frugivory: European Corvids as Overlooked Vectors for a Broad Range of Plants. Front. Ecol. Evol. | https://doi.org/10.3389/fevo.2019.00133