The return on the retraps

Individuals ringed on Nan Ron and then caught again on the island are low. For many they constitute the young 'wanderers' - those birds of insufficient maturity to breed who pop in to investigate the lures as representative of potential breeding sites and then move on to prospect elsewhere. Other birds captured of an age greater than 3 years old are considered to be breeders.

Of the four birds caught this year in this category all four can be considered breeders.

Results have been received on another 26 birds that were originally ringed elsewhere, now caught on Nan Ron. The four highlighted could be considered as breeders as all are greater than 3 years old - and thus should be breeding. It is possible however that they could be failed breeders for the year who are 'wandering' to explore more potential succesful breeding sites. 

And the Stormies.

 Firstly we were here to capture and ring Storm Petrels. In previous years we have targeted numbers - catching as many as we can because so little it still unknown about these little seabirds. This year we wished to slow down a bit and take more notice of the birds in our hands. Ageing and sexing Storm Petrels is a bit of a black-art open to a fair degree of subjective assessment. We wanted to see if we could add to this arguement. 

Second we want to try and understand how many Stormies use Nan Ron and how big the breeding colony(s) across the island actually are.

Ringing: Scotland being what it is we lost two nights of ringing, one to rain and one to gusty winds. We still had a 'night-out' with the gusty winds having a camp fire (without the fire) viewing the stars and Milky Way and watching the Perseids meteor shower.

The quick ones among you will know this is not Nan Ron - the tree is a give away.

Photo from www: https://www.almanac.com/content/perseid-meteor-shower

At the end of our visit we ringed 608 new birds with 68 retrap (all UK ringed birds). Nine of these birds were our own retraps from previous nights' ringing.

Of these new 608 birds 233 were processed for biometrics and closer inspection. We took wing lengths, weight measurements and inspected the shape of primary (number 10), for ageing, and the extent of white on the underwing, for sexing. We also recorded whether the bird had vomited, evidence of breeding (bringing food to young), had any foot loss, indicative of age, and whether they had a brood patch, which is evident in breeders and pre-breeders (inexperienced birds getting ready to breed).

Using the extent of white underwing for sexing we also took photos. The image below shows bird 2757487 which appears to be female - poor extent of white (in simple terms). However, we will need to go back and revisit this as we found that the strength of ones head torch very much influenced the (apparent) extent of white seen.

The shape of primary 10 (P10) needs reviewing as we had some birds of known age who 'appeared' to be much younger - P10 pointed instead of round. The brood patch presence, and its significance, needs more thought as every bird - all 233 - had a brood patch to some degree. For those birds caught without sound lure this would be expected /anticipated, but at least two-thirds were caught using a lure when we would have expected a higher percentage catch of non-breeding wanderers (and therefore no brood patch).

Still much to do (and learn).

Census: a detailed 'call-back' study was undertaken of most of the walls - they look ideal nesting sites. Surprisingly there was nothing! However, once we had sat and thought about it we considered that, maybe, because this was also the Barn Owl foraging area (it nests in one of the old buildings) that maybe they had been forced from this area. We next censored some of the rocks and gullies on the north of the island. Not only did we get call-backs but we also got:

An egg with a sitting bird (or at least a bird close by, later ringed, on two seperate days). This confirms breeding - only the second actual egg discovered in recent times. The egg date may be considered late but Stormies do have an extended breeding season with some chicks not leaving burrows until October. This egg may be a second attempt from a failed experienced breeder or the first egg of a newly breeding female. Next year we hope to censor the island in greater detail in this respect.

Of other birds a previous group had ringed all of the Bonxies - or so they thought - we still managed to ring two (one a young bird, one old) and we found one chick dead. Of the Greater Black-backed gulls ringed we also found one of these dead. During the fulmar census we came across a wandering, single, juvenile Greylag Goose - this went unringed as it appeared to be without parents and thus unlikely to survive. 

The end of another year - we'll be back. 

The team this year:

Steph (playback expert), Gerry (moths and springtails), Kenny (Nan Ron old hand and seawatcher) Jean (our ever dependable route to the island), Bob (data collector and lichen prospector), Alison (newbie, swimmer and yoga guru), Bekka (newbie, swimmer, biscuit hoarder and all-round helper), Liz (helped with the fulmar census, swimmer and kittiwake expert - pity there are no kittiwakes).

All apart from Jean are BTO registered bird ringers with Gerry and Bob holding S permits and appropriate endorsements. Everyone collected skua pellets.

The visit of 2021

 It was good to be back.....

...fortunately the island looked very much as it did before - the sheep were still there and the buildings still standing. The island was 'dry' with vegetation having grown little with, fortunately, very little signs of 'the midge!' As it was dry there was little evidence of sundew (we said we'd look for it) although butterwort was present, as were the orchids. This year for some reason there was a noticeable increase in the numbers and variety of mushrooms.

The sheep were still roaming about with lots of youngsters while, at the other end, a few signs of old age death. One unfortunate, near the camp site, had to be moved a little further down-wind.

There had been changes though - brought about my two winters of absence - with some rock falls causing noticeable differences. At the end of what we call, The Gully, there had been some movement which, after a scramble, gave a view of the Arch - which wasn't possible previously.

This year a team of seven eventually found itself on the island (thanks to Jean) with a few late drop-outs due to ill health. We had a hardy nucleus with us as some ventured a sea swim - on more than one occasion. 

Although we were on the island for the Storm Petrels we did do other things. We set a moth trap, performed a fulmar survey of the island (numbers much reduced on 2019) and undertook a play-back lure census of Storm Petrels around the buildings and at various other sites on the island (next post). We also collected every Bonxie pellet that we could for plastic ingestion analysis. Although the Barn Owl was still on the island (seen) we could find no evidence of any pellets. We also sampled for springtails and spiders - because we could - and started to catalogue the lichens, both on the buildings and rocks.