Little terns at Embleton

On Friday, the wind is still pretty strong from the north-west. We go out anyway, but get completely pasted by the spray and return to harbour after two hours.

We decide that, although we are both pretty tired and looking forward to a bit of time off, we will use the afternoon to do some watches on little tern feeding rates at selected points around their colony at Long Nanny. We watch them feeding up to about 6km south of the colony, and felt pretty confident that they were going no further than this. They seem to spend all their time feeding over the surf in sandy bays, plunging from very high above the sea into water that can be only a few tens of centimetres deep. We see plenty of fish being carried back to the colony.

The southern limit of their foraging trips appears to be the spectacular Dunstanburgh Castle.

Radio-tracking terns

We sight out early on a bright sunny day from Amble Harbour into reasonably light northerly winds. There has been a small development because the team of researchers from Newcastle University managed to get permission to attach radio-tags to some Arctic terns on Coquet Island. We passed the radio tags to them yesterday, and they managed to attach three of them to breeding Arctic terns with newly hatched eggs.

We ventured out firsth thing with our over-sized antenna to listen for these three birds. Not a sausage. We decided that it would be best to chase a few birds then have another go when we could get some confirmation from Laura, the PhD student.

Julie listening out for radio-tagged terns

We decided that we needed more data for Arctic terns, so would target them for our birds to follow. We started on the east side of the island and tried to detect and identify the birds in plenty of time, so that we could get the boat moving quickly so we wouldn't lose the birds. It has proved quite a challenge to identify the birds quickly. One of the things that is particularly helpful is to see the translucent underside of the wing, when set against blue sky. Common terns show a small translucent triangle in the crook at the trailing edge of the middle part of the wing. Arctic terns on the other hand show a long tanslucent band from the armpit to the wing tips giving a stipey appearance. Along with different shape to the birds, shorter bill and usually longer tail streamers for Arctic terns, this has proved particularly helpful for sorting out the terns early.














Common tern on the left and Arctic tern on the right. Note the shorter beak and more rounded head on the Arctic tern. It also has a thinner, more distinct black trailing edge to the outer wing. The wings look to be further forward on the body, the tail looks longer as well. Although not absolutely clear in these photos, the translucent patch on the common tern is confined to the crook in the trailing edge of the wing. While the Arctic tern also seems to show the same pattern, look at its further-away wing and notice that it is translucent in the out part of that wing too.

We managed to follow one Arctic tern around a large area, as it travelled from feeding flock to feeding flock, until it clearly had managed to feed itself enough and returned to the island, some 20km away. And boy did it shift. We had to travel at 30kn to keep up with it, but got the ultimate satisfaction of seeing it disappear into the colony. Graeme, the skipper, lost his favourite hat along the way. Once we'd seen it safely back to the island, we retraced our tracks to where we thought his hat came off. And there is was, floating happily on the surface, exactly where the GPS said it should be. Champion!

We managed to follow a common tern to its feeding area, pick up a large snadeel for its chicks and return all the way to the colony. We tracked another three Arctic terns, then returned to the island to try out the radio tags again. This time we managed to get a signal, but struggle to interpret what it could mean - the birds appeared to be in the colony, but we couldn't always here the signal. At times it seemed as if the birds were at sea, but we had no way of knowing from our position whether this was actually the case, or we were getting false readings. We tried waiting for the birds to leave the colony, but after an hour and a half, decided we needed a rethink to our tactics and strategy for tracking these birds.

We finished the day with two unsuccesful trackings of Sandwich terns (they must do about 40 - 45kn when flying downwind - too fast for us), then a single Arctic tern, followed only as far as a couple of feeding plunges. It's still proving easy to lose birds. On the one hand you don't want to get too close as to disturb them while trying to feed, but if you sit off to feeding area too far, it's very easy to find yourself too far away if they move to another feeding area (which they do if unsuccessful in any area.

We have noticed that all tern species are cueing in on feeding puffins (and other auks). We watched one Arctic spend about 10 minutes in the company of a feeding puffin, often swooping or plunging every time the puffin returned to the surface with its mouthful of sandeels. While this behaviour was quite extreme, we often see terns searching for prey homing in on puffins during their foraging trips.

Line transecting

After a bit of hand-wringing and a chat to Linda back in Aberdeen, we concluded that we wouldn't be getting much work done if we wait for the weather to be good enough to chase birds.

Although not as useful as following adults to their feeding areas, we could at least do some line transecting. This is a standardised survey where you pinpoint all birds you see as your boat follows fixed lines. This should really be done from a bigger boat, but we had already decided that it would be perfectly valid to do this from a smaller boat, because nearly all of the birds we would see would be flying (I won't go into the details of the methodological considerations here). We would take the range and bearing to each bird, so we could pinpoint more accurately where they were actually feeding.

The previous day, I had plotted out a random route worked out by Linda. As always, it's important to put these onto an Admiralty chart to ensure the route doesn't take us over any rocks or other obstructions.

Although the route was a bit bumpy in places during the day (Seastate 2 or marginally higher at times), and wet in the rain, we managed to complete seven transects. We found it a bit challenging at first - the first line had a lot of birds on it for the first 10 minutes - and we struggled to identify birds and write down all the details onto wet data sheets. But we coped. I am conscious that without a good way to estimate distance, that this method is dependent on us measuring distances to birds accurately, or at least consistently.

The comforting thing about the day was that we saw few birds over waters deeper than 40 metres, and the two northern-most transects we followed were almost completely devoid of birds, apart from a couple of individuals transiting at the coast.

All told, we felt we had done something useful, and have found something that will keep us occupied while we wait for the weather to go calm enough for us to follow individual birds. However, with the wind forecast to increase again over the weekend, we will have to wait until we can get out to sea.