Chiffchaffs! Why?

The three great mysteries of science: what is dark matter?  how did life begin? what's behind the green door? To this can be added a fourth: why do Chiffchaffs chase other birds?

It's something I see very frequently at this time of year. Typically a Chiffchaff will watch a  Blue tit and wait for it to take off. The Chiffchaff then chases the tit around the garden, exhibiting a piece of behaviour known as 'giving it merry hell'.

Why do they do it? They seem to expend a huge amount of energy on this, seemingly, frivolous pursuit. I've puzzled over this for, literally, decades.  Back in the 90`s I wrote to Jim Flegg at the BTO about this - he replied 'That`s easy - it`s defending a feeding territory'. To me that just doesn't ring true.

For a start they aren't fussy about their targets - I've seen Chiffchaffs chase a whole range of species including a Great-spotted Woopecker on one occasion.  It's like the feisty small boy at school, taking on all-comers including the class bully.   

If you were of an anthropomorphising bent you could almost imagine that Chiffchaff was having a bit of sport. Maybe it is in fact 'play'. This isn't to invoke a 'just for the fun of it' kind of explanation. A kitten chasing a woollen ball is 'playing'. Whatever the reason for the kitten's behaviour, 'play' is a perfectly good word to describe it.

I've discussed this Chiffchaff puzzle more fully here.

Knopper  Gall - a Francis Bacon-esque distortion of an acorn

Yesterday on my patch walk I was interested to find Knopper Galls on several Acorns.

If Francis Bacon had painted an acorn portrait it might look some like this. A warped, disfigured thing exploded into folds of wrong oak. Wronged Oak.

Galls could be seen as the plant equivalent of a cancerous tumour. The insect parasite controls  the Plant tissue acting as a habitat and food source for the larvae.

This particular Gall, produced by a wasp (Andricus quercuscalicis)  has a two-phase life cycle requiring both the Common Oak and the Turkey Oak. This  is the part  find particularly interesting - where are the Turkey Oaks?

I've  found a single sapling, on the patch - but there must be more - where are they? It's like the dark matter conundrum - we know it must be there because of other observations - we just haven't found it.

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