An afternoon beside a pool.

 We are lucky in Warwick to have a number of fantastic open spaces that contain a variety of different habitats and wildlife. Priory Park is parkland and woodland, the Racecourse is flat grassland with patches of wet patches and St Nicholas Park, although a municipal park aside from the large playing field it has a river, fishing lake and dipping pool.

Alongside Kingfisher pool is a small pond that was recently dredged and cleared. King Henry pool has now recovered and is a flourishing ecosystem with abundant emergent vegetation. At this time of the year it is a magnet for dragonflies and damselflies, they zip around hunting over the water and gently lay their eggs in the vegetation.

Focusing on just the small pool I was lucky enough to see several species. The most obvious were the ubiquitous Banded Demoiselles whose numbers are just starting to ebb. Of the larger species there were a couple of Emperor dragonflies. A male patrolled up and down in a set predictable pattern hawking for insects it would take and devour on the wing whilst a female flitted from area to area ovipositing. She dips the tip of her abdomen in to the water and injects the eggs on to a reed.

Female Emperor ovipositing

Several blue Black-tailed Skimmers were present and a single Four-spotted Chaser.

Four-spotted Chaser

The most abundant however of all the species were the small damselflies, hunting and mating. I only identified two species, Blue-tailed Damselflies and Azure Damselflies. Both are most active at this time of year.

Male and Female Azure Damselfly mating

In a small open patch of water were a mass of Whirligig beetles. These energetic water beetles were whizzing around on the surface like nobodies business. These amazing beetles spin around on the surface. It has a latin name that reflects its nature, Gyrinus substriatus, from the root of gyrate, which these beetles really do.

As if this wasn't enough i was lucky enough to spot a small pike. It couldn't have been more than 10-15cms long. It moved with effortless grace and came incredibly close. I was able to watch it as it stalked various tiny fish. Normally when I watch the large pike on my patch they tend to sit on the bottom and then pounce up. This young jack however patrolled at the surface and struck horizontally.

Young Pike

Of course there were also the birds, Swifts dipped down to feed across the lake and Chiffchaffs sung from the willows, there was also a Jay. 

It just goes to show how much life can exist in such a small space. Of all the species present during my hours visit I barely scratched the surface, a life time could be spent catalogue everything there and I already have that task to accomplish on my patch.

Jewels on the Wing

I have been collecting data on the wildlife of 'my patch' for over 15 years now and its about time I did a little more with that information.

At this time of year we are approaching the end of the Banded Demoiselle flight period and so I thought it appropriate to explore their population dynamics since 2003.

How has their population size changed over time? Has the time they first emerge got earlier or has the length of their flight period changed. I can answer all these questions in a series of graphs.

Graph 1 - Number of maximum individuals recorded each week

This graph shows that between 2003 and 2013 the population was fairly static at less that 150 individuals in flight er observation. This increases markedly in 2014 with number rarely dropping below 200.

Graph 2 Date of First Emergence

Over the 16 years of study there is very little change in the week number in which the first Banded Demoiselle is seen. The trendline does indicate a very small trend for slightly earlier emergence times but is unlikely to be significant.

Graph 3 Length of Flight Period

Whilst emergence maybe getting ever so slightly earlier the duration of their flight period has remained static at approximately 15 weeks (11-20) although it could be said that this has only become more stable since 2013 with the variance in data becoming less than preceding years.

Graph 4 Maximum Emergence

This last graph partners with the first to take a more in depth look at the change in population, Here the maxima count values for each year are plotted highlighting the rising curve.

So what does all this mean? Well we can say that the population of Banded Demoiselles at the Saxon Mill is stable and actually increasing year on year within the same defined flight period. These sort of studies are very useful at looking at patterns but only go so far. We need some other level of data to explain the changes. Is the increase in numbers due to a change in sex ratio, better food availability or a reduction in predators. This opens up new avenues for investigation, I am reluctant to introduce the spectre of global warming but it is in temperature dependent species such as damselflies that its effects can be noticed.

You have to be careful in analysing data as well. You need to know about the ecology of the species, Banded Demoiselles spend two years as larvae before emerging therefore the population increase seen starting from 2013 reflects an increase in eggs laid in 2011.