Warning! Reed Warbler Neighbourhood Watch
Whether you have one near you, are part of one, or have seen signs in other places warning that such an organisation are in operation, we have all heard of the ‘Neighbourhood Watch.’ When we hear those words, we know for the most part what is involved, local people collaborating with the police in order to keep their area safe. But here’s an interesting question, as humans are we the only animals to be involved in these ‘watches’? The answer? Apparently not. That’s right! Tell your watch to watch out, because there is a new neighbourhood watch in town and it’s run by these feisty feathered guys: the reed warblers.
But wait, reed warblers in a neighbourhood watch? Sounds ridiculous does it not? After all, excluding the odd sparrowhawk, what in the world do reed warblers really have to watch out for? Gangs of juvenile warblers, wearing hoodies, terrorising the locals and vandalising precious reeds? Of course not, but there is a very real threat that reed warblers have long recognised. His name? The cuckoo.
Along with other species such as the dunnock, reed warblers find themselves among some of the main birds species that seem to be targeted by cuckoos. A single cuckoo chick can decimate the nest of another bird, removing eggs and even other chicks from the nest, consequently removing any competition for food and survival. But, as cunning as the cuckoo is, reed warblers have caught onto their game and in some areas, they appear to have come up with unique ways of recognising the threat of cuckoo parasitism.
A new study, carried out by Dr Rose Thorogood and Dr Nicholas Davis seems to have collected evidence that shows this type of behaviour. By observing warblers at Wicken Fen for two years, researchers have realised that warblers seem to recognise the threat that cuckoos pose. One particular behaviour observed was the ‘mobbing’ of cuckoos by warbler gangs, whilst the warblers also raised awareness of the cuckoos presence to others through alarm calls. As with many animals, alarm calls alert others to a threat and cause other birds to come and investigate the problem. Therefore, the local population of warblers then becomes aware of the threat, and the reed warbler neighbourhood watch is very successful indeed. But this tale doesn’t end here, as reed warblers also show signs that they recognise cuckoo eggs, and even ejected them from their nests. Now, this may not sound so clever, but it is no mean feat, as cuckoos are master tricksters and their eggs are highly similar to the eggs of those birds that they target. However, through expert sleuthing skills that Sherlock Holmes would be proud of, warblers search for ‘clues’ that an egg in their nest may be the produce of an impostor. For example, if the warblers have already been alerted to a cuckoo in their area and should they have spied a cuckoo hanging around their own nest, they may chose to eject a suspicious egg.
But through all this, what of the big bad wolf of the story? What of the cuckoo? Although the way they breed is detrimental to other birds nests, the cuckoo itself is in fact suffering. Over the past 30 years, cuckoo numbers have declined by 60% and the reasons for this are yet to be determined. At Wicken Fen, which boasts hundreds of breeding reed warblers each year, around 10-20% of nests were targeted by cuckoos. Recently however, this number has dropped dramatically, to just over 2%. So, good news for the warblers! But not so good for the cuckoo. In addition, it would also seem that it is not just humans that have recognised the decline in the cuckoo. No indeed, as those clever reed warblers have also noticed that the threat of cuckoo parasitism has lowered. This has also been reflected by the research, as it found that reed warblers are actually far less likely to eject an egg from their nest today than they were 30 years ago. The risk that comes with ejecting an egg from a nest is very high, as there is the very real possibility that the warblers eject one of their own eggs. Therefore, as the threat of cuckoos has dropped, the risk of ejecting the wrong egg is higher and consequently, they are less likely to do so.
So, the reed warblers are doing well and they have sussed out the problem of those pesky cuckoos! However, those pesky cuckoos are in a bad way. Indeed, they are one of our red listed species on the Birds of Conservation Concern. Now, words associated with the cuckoo such as parasitism sound unfavourable, and can make the cuckoo out to be a kind of devil of the bird world, coming in and decimating the nests of others. However, although their way of breeding is not ‘typical’ and may not meet the ‘accepted’ ways of breeding, cuckoos are an important species that need to be protected. Compare the cuckoo with the warblers, reed warbler breeding pairs in the UK are around 130,000, whilst cuckoo pairs are only 16,000. Of course I am not accusing the reed warbler of being inconsiderate by foiling the cuckoo, but the fact that cuckoos are declining is an interesting point. The more information we can gather on the lifecycle of the cuckoo and any trends we can identify, such as those associated with the reed warbler, the more able we are at building a better picture of what exactly is going on.
Flashback. A few years ago my family spent the summer in a holiday cottage in Cornwall. I remember one particular night there was a raging storm with lightening, thunder, rain, the works! But in the morning, the storm had passed, the sun was rising and my windows were open out onto the fields outside. The smell of rain wafted in and I woke to the soft, continuous call of ‘cuck-oo…….cuck-oo.’ A now disappearing sound of the countryside….
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