27 February 2015

Eat like a Gannet

Along with all of the useful data coming into the Demography Team from the Nest Record and Ringing schemes, we also get some interesting or unusual reports. Our latest recovery from Dr Kees Camphuysen, Senior Scientist and Marine Ornithologist at the Nederlands Instituut voor Zeeonderzoek, is one of these:

"I was demonstrating a post mortem for Ecomare animal care staff tonight on an unringed juvenile female Gannet. It was originally found fresh dead on a beach on Texel, The Netherlands, in 2013 but was frozen to keep it in a fresh state until the post mortem."

Juvenile Gannet during post mortem - Dr Kees Camphuysen

"It was severely emaciated but this was not unusual of young Gannets at this time of year but I could feel a very lean and stiff "fish" in the stomach. It was not a fish however. It was a wing...a bird wing, heavily digested and the primary shafts suggested the bird was reasonably large. To my utter surprise, in the muddy blackish, digested remains was....a ring!!!"

The ring was put on a Fulmar chick on 4 August 2013 on Swona, Orkney by the Orkney Ringing Group. Considering this bird was found on 18 October 2013, this chick didn't survive very long. Kees and his colleagues believe the chick may have been eaten by a large fish, possibly a Cod, which was then caught by fishermen, gutted and the offal (including the remains of the Fulmar!) eaten by the Gannet. We will never know for sure what happened but it is very interesting nevertheless.

The contents of the Gannet including blackened feathers and ring - Dr Kees Camphuysen

19 February 2015

Happening in a box near you

National Nest Box Week kicks off every year on Valentine’s Day. It’s a week where the BTO encourage members of the public to put up nest boxes in their gardens. Our garden birds are just starting to prospect nesting sites in preparation for the approaching spring, so the sooner you can get a box up the better, whether you build it yourself or buy it from the garden centre.

Great Tit - David Waistell

There are increasing concerns that the availability of suitable nesting cavities is falling as old trees are felled and houses are repaired, so erecting a box could make a real difference to a pair of birds in your garden. However, the real conservation value of erecting a box is the opportunity it provides to safely record the progress of the nesting attempt, looking inside at intervals to count the number of eggs and chicks and submitting data to one of the BTO’s nest monitoring schemes. The benefits of your monitoring efforts will be felt well beyond the confines of your garden, benefiting national bird populations by helping conservationists to understand the impacts of climate change and urbanisation on the number of young reared and therefore, ultimately, on population trends.

Blue Tit nest - Hazel Evans

Nest Box Challenge  (NBC) is an on-line monitoring survey focussed on gardens, with the ability to record data on both box-nesting birds, such as Blue Tits, and open-nesting species, such as Blackbirds and Woodpigeons.  The Nest Record Scheme (NRS) collects more detailed data on all nesting species across a wide variety of habitats. People are understandably wary of approaching nests, but there is a very large body of research showing that the contents can be examined without a negative impact on the outcome of the attempt, as long as the guidelines set out in our NRS Code of Conduct are followed.

The number of people nest recording in the UK has never been higher, with almost 1,000 volunteers monitoring over 45,000 nesting attempts in 2014 alone through NBC and NRS. The Nest Record Scheme is now in its 76th year and in that time over 1.35 million nest records from 232 different species have been sent in, creating an invaluable and unique record of the UK’s breeding birds. These data are used to generate annual trends in laying dates, the number of eggs produced and the number of chicks reared, which are published each year in the BTO’s BirdTrends report. By analysing nesting data in conjunction with survival data generated by bird ringing, we can assess the contribution that changes in the number of fledglings produced makes to national population trends.

Blue Tit fledgling - Tommy Holden

By far the most common inhabitants of our garden nest boxes are Blue Tits and Great Tits. They have adapted so well to living in our man-made constructions that we receive thousands of records every year; so do we really need any more? The answer is a resounding ‘Yes’, as the better the coverage, the more we can explore the degree to which birds responses to changes in the environment vary between regions and habitats. Your help is vital in continuing to build on this amazing dataset, so why not make 2015 the year you start monitoring nests?

By Hazel Evans, Nest Record Scheme secretary

14 February 2015

The return of the Waxwing!

Ringer Peter Alker from Orrell, Greater Manchester, recently got in touch with the 'Demog Blog' team with some rather interesting news:

"It is many a birder’s dream to have a Waxwing visit their garden and that dream came true for me in February 2013, when one started feeding on apples I had put out for thrushes and wintering Blackcaps. One was soon joined by another, and the number steadily grew, peaking in mid-April with 220 birds chomping their way through 25 kilos of apples each day! Some birds stayed well into spring and the last three were seen on 8th May, by which time I had caught 265 birds, nine of which had been ringed elsewhere in the UK or abroad.

A Waxwing tree - Peter Alker

Waxwing - Peter Alker

Since then, people have often asked me if any have come back to the garden or if I think they will. I would always tell them that none had returned and that I thought it would be unlikely, even if there was another big irruption; such is the Waxwing’s reputation as an irruptive migrant in search of food. The number of Waxwings recorded in the UK this winter has been particularly low, so I was astonished, to say the least, when one turned up in my garden last Saturday (7th February), almost two years on from the appearance of the first in 2013. It was an adult female but, unfortunately, I wasn’t able to see if it was already ringed. It didn’t visit the garden the following day so I was relieved when it returned the next Monday and incredibly I could see it was wearing a metal ring. Grabbing a camera, I was able to read the ring number from photographs and it was a bird I’d ringed in the garden as a first-winter female on 23rd February 2013.

The key shots from the hundreds of photos taken.

On the face of it, the appearance of this bird was a bit of a contradiction as it seemed unlikely that it had returned to my garden by chance but on the other hand irruptive species are not known for showing any site fidelity in winter. I wasn’t sure if there had been any similar occurrences so I contacted Raymond Duncan, of Grampian Ringing Group, who has been colour-ringing Waxwings in and around Aberdeen since 1988. He confirmed that they only have seven records of birds returning to the UK in subsequent winters, from over 3,100 birds ringed there, and only three of these were to the original ringing site. One of these birds was ringed in Kintore, near Aberdeen in February 2009 and photographed back in the same village in February 2010; also a winter when there were very few Waxwings in the country.

Waxwing - Peter Alker

So what, if anything, could these records tell us? They may be the exceptions, but it seems to me that Waxwings have the capability to return to sites used in previous winters in certain circumstances, and it is the circumstances that are rare and not the ability itself. Most Waxwings will not need to move to the UK in search of food more than once in their lifetime, as large irruptions are relatively infrequent and Waxwings are not particularly long-lived. Their main food source of berries can vary in abundance in the UK, affecting the birds’ distribution and movements in search of food. They are a very gregarious species in winter and the behaviour of an individual will be influenced by other birds in the flock. These factors together reduce the likelihood of any Waxwing being found returning to the same site in the UK in subsequent winters.

The interesting point about these two birds is that both had returned to previously-used sites in non-irruption years. This might suggest that they were returning in search of other Waxwings and not just in the search for food. Lastly, a further factor in the case of my bird is the provision of apples. It was ringed on 23rd February 2013 and was retrapped later that winter (on 28th March), so had stayed over a month and probably much longer. The provision of apples for Waxwings is a relatively recent phenomena and experience of a long-term reliable food source may have played a part in the return of this particular bird."

04 February 2015

Unusual Winter Warblers?

During these cold winter days it is nice to think back to the summer full of the song of the Whitethroat, Willow Warbler and the reeling Grasshopper Warbler. Whilst most warblers migrate from Britain & Ireland to enjoy the warmth of their African wintering grounds, some migrate from Europe to spend the winter here. Blackcaps have been commented on before, here, here, and here, but they are not the only warbler species seen here in winter.

There are usually quite a few Blackcaps and Chiffchaffs seen in the country at this time of year, with the odd Yellow-browed Warbler present in the south. However, last Friday (30/01/2014) a Reed Warbler was caught at Chew Valley Ringing Station, North Somerset! This bird should have been in Sub-Saharan Africa at this time of year. There is one previous electronic record of a Reed Warbler being ringed in January (a bird ringed in Hertfordshire in 1981) whilst there are two records of birds ringed in December (2000 and 2003).

The graph below shows the average number of ringed Reed Warbler, Chiffchaff and Blackcap over the last five years. Reed Warbler just makes an appearance in November but is swamped by the over wintering Chiffchaff and Blackcap. Birdtrack data show a similar pattern in the seasonal abundance of these wintering warblers.

There are many parameters that govern the over-winter survival of these birds and there are clear differences between years. Temperature can greatly affect food resources, especially for insectivorous species. The graph below shows the number of Chiffchaff ringed in winter and you can see the figure for the winter of 2010/2011 (which was very cold) drops substantially.

Numbers ringed during November appear to have increased recently, but this is not reflected in late winter catches. This suggests that more birds are arriving in the UK, but either dying, moving on southwards or dispersing into areas away from ringing hotspots like sewage works that are already at carrying capacity. More systematic winter ringing across a wider range of sites is required to identify which of these mechanisms is responsible.