Disruptive camouflage

The response of birds to a sparrowhawk alarm varies.  Most small birds flee into dense cover if they can, hoping that the hawk won't be able to follow them.  A great spotted woodpecker reacts differently - it freezes, not moving a feather. At first glance the woodpecker's reaction seems almost suicidal but it relies on the fact that a sparrowhawk's eyesight is tuned to detect movement with relatively poor colour vision.

Only when the danger has passed will the woodpecker dare to look around to check that all is clear.

Of course most alarms are false alarms but it pays to be cautious.

To our eyes its black, white and red colouring makes a woodpecker very easy to see but in fact it is taking advantage of its disruptive camouflage.  The bold patterns break up the outline and if the woodpecker doesn't move it is difficult for the sparrowhawk to see it, especially in dappled light in woodland.  A similar idea was used to protect Allied merchant ships in WW1.  Known as dazzle camouflage, ships were painted in bold confusing patterns which made them harder to see through a German periscope.  Even if they could be seen it was difficult to make out which was the bow, confusing assessment of the ship's course and making it hard to predict the aim of a torpedo.  Dazzle camouflage was invented by English artist Norman Wilkinson and this painting is by another English artist, Edward Wadsworth, who was also responsible for making the designs for the ships.

This is the SS West Mahomet in dazzle camouflage 100 years ago.

Of course it didn't always work in the war, just as it doesn't always work out for the woodpeckers.  Whether that's because they lose their nerve and move, or whether the sparrowhawk can sometimes see them anyway is hard to say.

The outliers

European hornets are long established in the south of the country and, like many insects, their range is spreading northwards.  The 10 km blue squares on this map from iRecord show all UK records for Vespa crabro this year.  The wiggly blue box delineates our local vice-county, South Northumberland (VC 67).  Note that the rectangular blue symbols in Scotland and Ireland are motorway numbers - they have no hornets.

Our hornets are shown in two blue boxes at the top because data were entered by two people (the other being the vice-county recorder for moths) at points 50 m apart in the reserve and, by chance, the two points are in different 1 km squares which are in different 10 km squares!  Hence two blue boxes.

As you can see from the first map, our hornets are way outside the previous recorded range (90 km from the nearest data point in Yorkshire).  When I entered the record of our local hornets, with a photo, I got this response, although the record has since been accepted.

It is intriguing to consider where the hornets came from.  It is possible that they have been around for a while and no-one noticed although that seems unlikely as they are pretty obvious, being large, yellow and noisy.  iRecord data go back 10 years and contain only one other record for the county, 40 km farther north in Harwood Forest in 2015.  That record has no supporting photo and from the details provided it seems unlikely to be correct.

A second possibility is that the foundress queen for "our" nest flew the 90 km from Yorkshire, possibly wind-assisted.  I don't know how far European hornet queens are prepared to fly but I have read that Asian hornet queens (Vespa velutina) in France can spread at up to 60 km a year.

The third possibility is that the queen that founded our local colony hitched a lift during hibernation.  There is a large bakery and food factory just across the road which presumably imports a lot of material on pallets, etc.  We know that the Asian hornet arrived in France from China in a consignment of pottery in 2003 or 2004 so maybe our European hornet hitchhiked from the south in a similar way.

If these hornets are true outliers there is some concern about how they might fare in subsequent years.  Depending on how the queen of this colony was mated (and most queens mate only once) there is a fairly high chance that most or all of her offspring are full siblings. This means that matings of the males and new queens raise the prospect of inbreeding weakening later generations. Male hornets, like all other male wasps and bees, are haploid, that is they have a single set of chromosomes.  All females (workers and queens) are diploid, with a double set.  If my calculations are correct, theoretically sibling mating will lead to 25% of the next generation having two identical copies of the sex-determination gene so rather than being female workers they become diploid males, meaning that they are a drain on resources, and thus weaken the colony without contributing to the genetic line or the workforce.  The proportion of diploid males increases to 33% in each of the following two generations (the maths is quite complicated so I haven't gone any further than that).  In theory this would be bad news but the European population of Asian hornets is all thought to have come from a single foundress queen and it doesn't seem to have done them much harm, even though they do produce quite a lot of diploid males.

A walk round the pond - week 44

Back by popular demand (thanks Cherry and Julia), for one week only.  I had thought last week's post would be the last but for completeness I went to the pond again on 1st November.  It was sunny and calm but only 7℃.  Despite that I saw at least half a dozen male common darters and a couple of females.  The males were quite active, with a fair bit of aerial combat in between basking in the sunshine.

I will go again next week, but won't post again here unless there is something extraordinary.  Since the start of the season I have been collecting data for weekly reports to the British Dragonfly Society via iRecord.  It has been interesting to document the appearance of the various species.  As last year, there have been 15 species in all - 6 damselflies and 9 dragonflies.  With the exception of banded demoiselle, which I saw only once and which is a visitor from the nearby river, I think all are probably resident breeding species, although I have never seen juvenile or female black darters here.  This chart gives a summary of the appearance and flight season of all 15 species from week 18 to week 44.

If I do the same again next year it will be interesting to compare the results.  I will go again next week, and perhaps the week after, to document the end of the season.  After that it will be six months before I see a dragonfly again - and I expect it will be a large red damselfly in early May.

Up close and personal

The hornets are still around but in smaller numbers.  I now think the nest must be a bit farther away in the woods than we first thought.  The most hornets visiting the maple syrup at one time was eight, whereas there are probably a couple of hundred in the nest.

We have still only seen two males but I think some of the larger females must be new queens.  These are probably all workers.

Workers were still hunting just over a week ago, which meant they were still feeding larvae, and as the pupation time is around 15 days new hornets will still be emerging next week.  However, if they don't visit the maple syrup or the ivy flowers in the warden's garden it will be very difficult to tell what is going on.  Let's hope we see a few more.

A few more squirrel photos

I have had time to process more squirrel photos from last week.  I was able to watch this squirrel feeding for 15 minutes.  It seemed to be taking pieces of fungus on the bark from underneath the branches and sitting on top to eat it. At times it was hanging from a branch by just the claws on its hind feet, completely fearless and ignoring the 50 foot drop to the ground.  Squirrels have ankle joints that can rotate 180° to enable them to do this and to run headfirst down tree trunks.  It is amazing to watch.

A walk round the pond - week 43

This feels like the end of the season.  It is cold this weekend and cold weather is set for the next few days at least.  I went to the pond at the beginning of the week and even then I could find only one dragonfly, a solitary male common darter.  He wasn't flying, perhaps he didn't have the energy.

There were no butterflies and no bumblebees.  Despite that, there were still a few flowers, hoping for a late-flying pollinator.

There were also plenty of fruits in the trees and hedges.

The two mute swans were still present and seem to have settled in.  I hope they stay.

The only other animal I saw was a tiny frog, no bigger than my thumbnail.

I think this will be the last in this series of posts on A walk round the pond.  I started in week 13 so that's 31 weeks in a row.  It has been fascinating to watch the changes in and around the ponds over three seasons.  I will continue to visit regularly but I am not sure what to do for next year's blog.  I could just repeat the weekly reports as the weather is likely to be different from this year's cold winter, wet spring and hot summer.  Another idea is to do a monthly report from January to December.  I'll have a think about it.

Good news and bad news

First the good news.  These photos were taken yesterday in Gosforth Park Nature Reserve, less than a mile from here as the crow flies.  This is first time red squirrels have been seen in the reserve for several years and it is more than two years since I saw one in my garden.

Then the bad news.  Twenty seconds after my first glimpse of a red squirrel and 20 yards away I saw an American grey and over the next few hundred yards in the same patch of woodland I saw several greys.  They took over in these woods and ousted the reds more than 10 years ago.

In recent years there have been concerted efforts to control the greys in and around Newcastle with limited success. Red squirrels are absent from most of England and we are on the front line of the battle between reds and greys. Generally the two species don't coexist for long but if greys can be controlled or removed the red squirrels can get re-established.  There continue to be sporadic reports of sightings of reds in and around the city so we are encouraged to keep up the efforts to support them.