It was a fantastic start to the morning. I’ve managed to somehow avoid ever seeing a Black Tern on the Exe estuary, despite them being annual and having spent a considerable amount of time looking over the water. For some reason it’s been a bogey-bird for me. So a week or more ago, when my good friend Matt found White Winged Black Tern – only Devon’s 15th record ever – I became one of the few birders to have this rarity on my life list before Black Tern! This morning however the world was restored to normality as two BTs appeared off the seafront and I could confirm my tick. But much better than that, for a good hour all three birds were feeding near each other and on occasions we had all of them together in the same scope view – a truly amazing sight and a once in a life-time opportunity for an inexperienced birder like me to compare these potential confusion species side-by-side and to see how they interact with their environment.
Matt’s notes do more justice to this comparison than I can here and I consider myself lucky, as always, to know someone so expert who can put me on to these birds. Such expertise is built up over many years and ‘finding’ birds isn’t by chance. Partly it’s time; time spent watching, searching, being there in case. But it’s also about knowing how the world of birds works; what should be where and when; what could be here; how tides and winds and rain might bring in birds, or drive them under cover. It’s about being at home in the natural world and having a feel for things – understanding the ‘jizz’.
All this set me thinking about ‘ecosystems’. The derivative ‘eco’ permeates our culture, as a short-hand for anything ‘good and green’, but this tends to over-simplify the meaning. The word is derived from the Greek oikos meaning home/family. Literally, understanding the system by which home/family is established. This feels just right in describing birding and mothing because it’s more than just knowing about things. Fundamentally it’s about understanding how things come to be ‘at home’ in their environment, and how the environment provides a space to make this home; how species and physical environment fit together, and how we can be part of it all too.
This morning’s activity illustrated the idea perfectly. Both species are ‘marsh terns’ rather than sea terns, meaning that they are more at home feeding on lakes, still waters in estuaries and so on. Rather than diving for fish they surface feed, fluttering and twisting over the water looking for insects and other life at or near the surface. Breeding in Eastern and Southern Europe, they are migratory in the UK (bar a few occasional pairs) and so the fact that they have made their temporary home in Exmouth relies on finding enough food to keep them here for a week or two. The exact diet I can’t say, but perhaps it included these insects, this one found (with a damaged wing) on the coast path as we scoured Orcombe Point for other migrants.
I’m keen on hoverflies, though still a complete novice, but some ID work at home revealed this is as Scaeva pyrastri (Pied Hoverfly). It’s relatively easy to ID with the key features shown below, namely …
Hairs on the eyes – visible below as a yellow/white blush on the eye surface.
Protruding space between the eyes, with bulbous antennae:
And of course the characteristic white ‘comma’ marks on the abdomen.
Ball and Morris (2015) state that it’s a migrant, like the terns, arriving in large numbers in some years in July and August, and occasionally breeding too. I don’t want to draw too strong, or unwarranted, connections between Black Terns and Pied Hoverflies, but in general terms these connections between species are everywhere and crucial to survival – the ‘system’ of being at home.
However, to a casual observer, or even a careful one who only looks at one animal/plant group, they may not be apparent. Earlier this week I came across an article in the Journal of Insect Conservation and Diversity (one of the perks of working in a university is access to all sorts of this weird stuff!). It reports on the manner in which ‘Livestock grazing disrupts plant–insect interactions on salt marshes’. You can see the abstract here, but in essence it describes a study of grazing densities (number of sheep per hectare) on a German saltmarsh and the effect on both plants and insects. In a nutshell it finds that increasing the density of sheep has limited effect on plant species composition – there still plenty of plants of different sorts and though grasses tend to dominate, other species readily survive the grazing impact. If you are only interested in plants then you might think all is ok … but look at the composition of moths (as the study did) which are making use of these plants and you find that increased grazing has a significant effect on decreasing moths species. It turns out that it’s not the number and variety of plants that seems to matter for moth survival, it’s the way insect-plant interactions work, and how they are disrupted by grazing animals. Unless you are a specialist grass moth, like this Chrysoteuchia culmella, say, then grazing stops you interacting with the species of plants you rely on, even though they are still there.
It’s an ecosystem in action – a network of ways in which species can, or cannot, be ‘at home’ – and anyone interested in birds should take note since lots of reserves are based around marshland and grazed: think Exminster, Topsham, Slimbridge etc. Lots of cattle or sheep and the plants are fine … but the interactions between plants and moths (and hoverflies) are reduced … and terns feed on moths and hoverflies …
One thing I take from all this is the importance of being interested in different animals/plant groups – pan-interest, if you like – but also the difficulty of seeing ecosystems in action. It’s always easier to see ‘things’ than connections between things, and even harder to see the absence of things! I can see the terns (finally!), I can see the hoverflies and I can see the plants, but seeing a decline in interactions between them is challenging. So after a great start to the day it also ended well as I noted on Twitter that the National Moth Recording Scheme, made up of data from amateur recorders like me, has just today had its 24 millionth macro moth entry logged. Big data sets make for good analysis and absence is always easier to see on the grand scale. I like to think my 2000+records to date are making a difference.
Ball S and Morris R. (2015) Britain’s Hoverflies: A Field Guide: Princeton University Press.