Blackcaps Eating Soil

 from Alwyn Jackson

On the BTO’s Blog Garden Birdwatcher Christopher Wren recently published photos of juvenile Blackcaps eating soil in his back garden.  He wrote “I have been very intrigued to watch young Blackcaps in the garden this week.  They were eating woody nightshade berries which are poisonous.  Immediately after eating the berries they were flying down to a patch of bare soil and picking up small bits of earth.  At first I wondered if they were looking for insects but it was clear they were swallowing the soil. I think the Blackcaps are probably all juveniles although some have better developed feathers than others – possibly from first or second broods.”

In response a member of the BTO staff replied, “Soil eating is known as geophagy, literally earth swallowing, and is observed in many types of animal.  It is common behaviour in many herbivorous mammals as a way of providing essential minerals otherwise missing from their diet.

I found an interesting article by Jared Diamond reviewing reasons why birds (in his case parrots) might eat soil.  They include (1) to assuage hunger, (2) to help grind up swallowed food, (3) to buffer acidic or alkaline foods, (4) to counteract viruses or bacteria, (5) to provide essential minerals, and (6) to detoxify plant poison.

Of these I wondered if the last is the explanation in these Blackcaps.  Woody nightshade berries are toxic and the other birds in the garden seem to avoid them.  Then I found this extract in a book called “Birds and Berries” by Barbara and David Snow:- “Woody Nightshade elsewhere.

“We have found no published references to birds eating the fruit in Britain that add significantly to our findings: in fact records of any sort seem to be extremely few.  There are scattered records from continental Europe which indicate that August and September are the main months when fruit is eaten.  As in our area, the Blackcap seems to be the dispenser of the fruit (several records), with single records for Blackbird, Garden Warbler, Stonechat and Wheatear; and there is a single record for the Jay in January.”

So it seems that Blackcaps deliberately seek out the woody nightshade berries.  I think the probable explanation for what I have seen is that the Blackcaps are eating poisonous fruit and then eating soil as an antidote.  The question is why didn’t they just eat the blackcurrants, gooseberries and raspberries like the other birds do? They must get something out of it.”

Have any WVBS members observed this or any other interesting or intriguing behaviour I wonder?

If so why not pen a few lines for the newsletter and share your observations with other members.

Any comments would be welcome.


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