Exposing the copy cats

I’ve had a question on my mind for a while that required some investigation.  It all started back in late April when I heard our friend the ‘willow-chiff’ again.  This is a willow warbler that can be found down in Botany Bay, who likes to throw in the odd “chiffchaff” at the end of his willow warbler song.   I believe it is not uncommon for these two birds to weave the song of the other into their own.  A few weeks later, when we started monitoring our bitterns I was perched overlooking New Fen North, listening to a reed warbler who was sometimes interrupted by a bearded tit.  Eventually, I realised that there was no bearded tit and in fact it was the reed warbler.  The warbler had two or three different song patterns that he repeated over and over (and over – he was a persistent chap!) and one of these ‘loops’ contained bearded tit ‘pings’.  With a bit of looking I picked out the particular reed warbler that was doing this and watched him emit these sounds, just to confirm that I was hearing correctly!

Photo credit: Bearded tit and reed warbler both by Tim James, 'artfully' merged by Ali Blaney

A few weeks after that, during another bittern watch overlooking Joist Fen North, I could hear all sorts of birds singing and calling.  I was positioned in the middle of the reserve so had reedbed 360 degrees around me, which involves a lot of head turning for these surveys!  As we also record marsh harrier activity, I kept looking behind me to try and spot the harrier that called every so often.  But I could never find it.  My ears eventually registered the fact that the sound was coming from down behind me and not up in the sky or off in the distance to the south.  It was another reed warbler and this one enjoyed throwing in the call of a marsh harrier mid-song, along with the usual reed warbler notes.

A quick conversation around the office and the list of bird mimics increased – David has heard a jay imitating a buzzard and a reed bunting in New Fen North trying to convince us he’s a green sandpiper.  And of course there is our famous Lakenheath Fen blackbird, who does a fantastic impersonation of a golden oriole, much to the confusion and frustration of everyone!  This prompted me to investigate why a bird would imitate the call of a predator, as well as those of other birds.  We're all aware of mimicry (which is also related to camouflage) in nature, particularly with insects.  But imitating the call that a marsh harrier makes when it's bringing in food for a juvenile or an adult at the nest seems to me like it would potentially draw in other marsh harriers, so why would a reed warbler benefit from making this sound (even though a reed warbler isn't usually part of a marsh harrier diet)?

Photo credit: Buzzard by Rob Nichols and jay by Les Bunyan, 'skillfully' combined by Ali Blaney

A quick search of the internet revealed (along with a huge amount of information about different types of mimicry throughout nature that I definitely don't have room for here...) the following possible reasons for bird mimicry:

• To attract a mate – the ability to mimic others demonstrates intelligence and an ability to survive long enough to learn a variety of tones
• Territory defence – as well as highlighting the strength of the resident bird, mimicry suggests there are more birds in the area than there really are, meaning other birds may be reluctant to try and stake a claim in that area
• Protecting a food source – mimicking a predator may scare others away and prevent them investigating a food source
• Nest protection – mimicking a predator may deter other birds from approaching the area if they consider it to be dangerous, giving a better chance of survival for eggs and chicks 
• Social integration – as well as learning their initial basic repertoire from family and other birds of their species, baby birds will also learn mimicked sounds.  This helps with social acceptance and at a later stage, territory defence and attracting a mate
• Accidental learning – birds will sometimes pick up songs of other species (and even machinery, human sounds etc) simply due to their proximity.  This is quite common with birds in an urban environment but would also be likely in a nature reserve, where many birds will squeeze into the available habitat - it might be the only suitable space in the area!

Many interesting reasons then why we have so many copycats here at Lakenheath Fen.  The reed warbler in New Fen North who was imitating a bearded tit could have been demonstrating his prowess at survival and his intelligence to try and attract a mate.  The more recent reed warbler mimicking a marsh harrier could have been trying to add an extra layer of protection to a nest site.  Maybe they just like the different tones and decided to spice up their own song!  Something else to think about while we're out enjoying the sounds of nature.  Have any of you encountered interesting mimicry on your birding travels, or even in your own garden?

I'll just finish with a quick apology to the amazing photographers whose photos I have butchered for the sake of this blog: Tim James, Les Bunyan and Rob Nichols!