Ever wonder how the thousands of seabirds that visit our coasts each summer are counted? Doug Gilbert, Head of Reserves Ecology, gives us some insight.
Counting seabirds: Start at 1 and keep going
Counting seabirds – start at 1 and keep going! All very well but how do you keep track of numbers in a vast colony on a vertical sea cliff? Well there are a number of different ways depending on the colony size and habitat and most importantly the species that you are counting.
Cliff nesting birds that build obvious nests, for instance kittiwakes, gannets and shags are relatively easy. By counting the number of “Apparently Occupied Nests” or AONs in the trade, you can easily estimate the number of pairs on the cliff. In very large colonies you might only count a small plot on a regular basis to give an indicator of how numbers might be doing in the rest of the colony.
Kittiwake and shag by Andy Hay (rspb-images.com)
Guillemots don’t build any nests although they do defend a small section of cliff ledge as a territory. The best way to estimate the numbers in a consistent way which can be repeated year after year is to make several counts of all the individual guillemots present over a period in early to mid June. This is when adult attendance at the colony is at a peak. The number of individual birds present is then averaged, or a best estimate is made if the weather or other conditions make some counts less reliable. Converting this into an estimate of pairs rather than individuals is a bit less reliable than counting AONs but we can still compare numbers over time to look for declines or increases. Razorbills are counted in the same way but they are often hidden away in rock crevices on the cliff so are more difficult!
OK, but what about puffins? They lay eggs and rear their young at the end of a burrow which you can’t see in to! To make things worse, lots of puffins that are not breeding visit colonies and hang around getting their pictures taken by visitors. How do you find out whether the breeding numbers are changing? The technique is not easy but it is possible with patience and skilled observation. By using photographs of sections of the colony and marking burrows that are being used regularly by puffins carrying fish, you can estimate how many burrows are occupied by breeding pairs in any one year (Apparently Occupied Burrows or AOBs). Over several seasons it is possible to follow trends in numbers in a particular colony or area. This does take a lot of time though and is only done in a few places where counters are available.
puffin by Andy Hay (rspb-images.com)
Right then, what about storm petrels and manx shearwaters – not only do they breed in burrows but the non-incubating adults only visit at night! Monitoring the numbers of these birds is extremely tricky and the best technique we have involves playing a tape recording of the species concerned at the entrance to their burrows and recording how many birds respond to the call. We know that not all petrels in burrows respond so working out what the numbers mean is a matter of statistics based on average response rates – and get this – each colony might have a different response rate! So using a response rate from one colony might not give you a very good estimate at another. Male and female petrels also have different response rates so it gets even more complicated!
Many gulls and skuas nest on moorlands on the ground so surveying them is often a matter of watching from a vantage point and counting the numbers of territories you can see using the birds behaviour as clues.
Arctic skua chick by Andy Hay (rspb-images.com)
Counting seabirds can be smelly, exciting, cold and intriguing work but when you are back at the office and you can add a dot to a map or a point on a graph showing this years results, it all makes it worthwhile.
Counting seabirds has never been so important a task as it it is now. With many seabirds in real trouble, all that effort by hundreds of people over the years across Scotland gives us the raw data that we need to show politicians the desperate need for better management of the marine environment, including the designation of Marine Protected Areas (MPAs), and more action on climate change.
Conservation Manager, Stuart Benn, with a roundup of his season on the hills.
No, not the Radio 4 chat programme nor the 1980s R&B group but time for an end of season tie up of some threads left hanging from previous blogs.
I always get mixed feelings at this time of year when all the surveys have been done – relief as it marks the end of a really busy time but sadness too as it marks another hour of the clock ticking by. Each year, I make sure I get out as much as I can and I’ll keep doing that whilst I’m still fit and able for “summer’s lease hath all too short a date.”
To begin at the beginning, my very first blog was about planting for insects – little did we know back in mid-April that we were set for a cool, wet spring and summer, one of the worst on record for butterflies. But, just in the last few weeks as it’s warmed, Small tortoiseshells, Peacocks, Small whites and Speckled woods have come out and made straight for the pollen. Hornets, hoverflies and bees didn’t seem to be as bothered by the weather and right from the start made a bee-line for the flowers - so much so that the garden can be heard just as much as seen and smelled. I get real satisfaction from knowing that those insects wouldn’t be around us without those specially chosen scabious, bugloss and the like. Talk about getting a buzz!
Small tortoiseshell butterfly
At the weekend I was taking a look around some of the glens that I’d done Ring ouzel survey this year – very quiet and all I saw was one fledged youngster where before the air had been filled with their ringing songs and most seem to have now headed south en route to their winter home in Morocco’s Atlas Mountains. But the surveys went well and, in the end, my four areas produced 0, 2, 6 and 7 territories so in the Monadhliaths, at least, they seem to be doing just grand and it’ll be fascinating to see how my figures fit into the national picture.
Last week also saw the final trip to the Common scoter lochs and gave a very disappointing lack of any adults or young – lots of work still needs to be done on what’s going on here and how it can be turned around. In my previous blog on the scoters, I talked about trialling different count methods (from land/boat, from the air and taking aerial photos) – looks like the land/boat counts are by far the most accurate though we may do another trial ‘cos, if we can get the air surveys to work it’ll save a lot of time and money too.
I’ll come back to Slavonian grebes in a future blog as there’s lots to say and there’s still no word on when the divers or eagles are going to be on the One Show but we’ll let you know as soon as we do! But I can say that those eagle chicks are doing well and have flown the nest – I took a wee look at them a couple of week’s back and they’re looking good!
Prime Ring ouzel habitat.
But I’ll finish this short look back with my two stand-out moments from some great memories of the 2012 season. The first was in early June when I was out ouzel surveying and taking a wee breather. When I’m in hill country I make a habit of scanning ridges just to see if anything is about. On this occasion, I picked up a young pair of eagles some 5 kilometres away and the male was doing a bit of display which consists of a series of steep dives. I kept looking through the binoculars and followed them as they came towards me – how quickly and effortlessly they covered those kilometres! Before long they were looking pretty big in the bins –no wonder, they were right above me! Then, and I’m sure the bird did it for fun, the male started displaying by stooping right towards me before pulling up (still a couple of hundred metres above me) and then starting over again. The sight of an eagle heading right towards you at speed is quite a thrill and not something I’ll forget in a hurry!!
And my second top moment was just at the weekend there. I was almost back at the car after a few hours on the hill and noticed there were a lot of Black darter dragonflies about. Rather than just walk by, I stopped and watched them for a wee while. The way the sun glinted off their wings and turned them to molten copper was just beautiful and every bit as arresting as that displaying eagle.
So, just two of mine - I wonder what your favourite moments with nature have been this year?
New blog from trainee Ecologist, Gordon Bryden. He's been out and about looking for hoverflies at Loch Leven.
Hoverflies at RSPB Loch Leven
Hoverflies are one of the most distinctive fly families, and definitely the most popular. They are mostly big and colourful bee and wasp mimics with a distinctive hovering flight around flowers and sunny spots. Many of the species have larvae which eat huge numbers of greenfly, making them very popular with gardeners too and they are vital cogs in ecosystems. A significant number of the UK’s hoverfly species are rare, making the group really important for conservation as well.
I took advantage of a brief break in the weather to head out to RSPB Loch Leven in Kinross to look for hoverflies. Loch Leven has an interesting mix of wetlands, woods, flower patches and hills so there are lots of habitats for a wide variety of species. Flowers are usually the best place for finding hoverflies since the adults will gather around them to stock up on nectar and pollen.
Far and away the most common species on site was Eristalis pertinax, shown above feeding at a flower. As you might guess from the picture, hoverflies are important pollinators since they visit so many flowers. Bizarrely this is one of the species whose larvae are the “rat-tailed maggots” which live in oxygen free sludge filtering out microbes to eat. I think that’s a much more dramatic change than any butterfly.
This is one of the aphid eating hoverflies. It’s hard to be sure from just a picture, but I believe this particular species is Platycheirus albimanus. Like Eristalis, the adults are completely vegetarian and feed on nectar and pollen. The larvae are important predators of greenflies and other aphids. Little flies like this probably eat far more aphids than ladybirds do, but get almost none of the credit.
Although it’s not a hoverfly, I just couldn’t resist taking a (blurry) photo of this Garden Tiger moth. Once a very common species, it’s numbers have dropped massively in recent years to the point that it’s becoming rather rare. It’s good to find one at Loch Leven.
Just to be thorough I climbed all the way up to the top of the hill in the Loch Leven reserve to check for hoverflies. It was much taller than I thought it was (much to the dismay of the volunteer I had shadowing me), but the view of the wetlands was spectacular. Sadly there weren’t any hoverflies up there but I made sure to snap a photo as a souvenir. In the end I found 13 different species of hoverfly on the site in just one day. No rare species this time, but it does give us a clearer picture of the ecology of the reserve.