23 June 2015

A Knot eggstravaganza

Delaware Bay, on the east coast of America, is positioned on the West Atlantic Flyway and is the final staging area for many thousands of waders on their migration from their South American wintering grounds to their Arctic breeding grounds. In spring, the Bay is also home to Horseshoe Crabs. These prehistoric-looking creatures spawn on the beaches in their thousands and their tiny eggs are full of protein – just what hungry waders need to replenish their body fat and to provide them with enough energy to complete their journey north.

The Horseshoe Crab eggs that the birds rely on. Photo by Ruth Walker

Unfortunately, for a number of complex reasons, the shorebird populations have diminished in recent years. As a result, in the mid-1990’s, Wash Wader Ringing Group members helped American scientists to establish the Delaware Shorebird Project. The project aims to research and monitor the health of the wader populations on the Delaware side of the Bay in order to better understand the connection between the birds, Delaware Bay and the Horseshoe Crabs. A sister project runs concurrently on the New Jersey side of the Bay. The birds use both sides of the Bay to feed, often swapping shores to avoid inclement weather. The data gathered are helping to identify and protect the resources that are so critical to the success of the wader migration. In part due to the work of the project, the key target species for the project, Red Knot, has recently been officially recognised as ‘threatened’ by the US Fish & Wildlife Service.

Red Knot. Photo by Ruth Walker

Location of Delaware Bay on the Red Knot's spring migration route

A number of BTO ringers, including BTO staff, still travel out to Delaware each May using their holiday time to volunteer alongside other researchers from around the world on this important project. The study aims to catch and fit individually coded colour flags to 350 individuals of each target species each year: Red Knot, Ruddy Turnstone, Sanderling (all of which are colour flagged) and Semi-palmated Sandpiper (though these are not flagged on the Delaware side of the Bay). Samples of Dunlin and Short-billed Dowitcher are also ringed and measured if caught. During their time in the Bay, birds can double their body weight and therefore catching birds throughout the season is vital to ascertain their fitness levels. In order to survive their migration, it is thought that Red Knot need to weigh at least 180g when they depart (having arrived a couple of weeks earlier weighing 110-120g).

The very similar looking Semi-palmated Sandpiper (left) and Sanderling (right). Photo by Ruth Walker

We aim to ensure that approximately 10% of the Red Knot population passing through the Bay are flagged, along with smaller percentages of Ruddy Turnstone, Sanderling and Semi-palmated Sandpipers. Because waders are global travellers, flagging projects are undertaken in a number of different countries. The flag colour indicates the country the bird was flagged in, so birds caught in Delaware have a green flag, but we also see birds with red (Chile), orange (Argentina), blue (Brazil) and white (Arctic) flags . We attempt to catch approximately every three days so that we have weight samples throughout the stopover period, with the rest of the time spent counting the numbers of birds using each of the beaches each day, re-sighting the colour-flagged birds as well as the seemingly endless task of entering and checking all of the data. Re-sighting colour-flagged birds not only gives information on arrival and leaving dates and movements of individual birds within the Bay, but also information on survival and the total number of birds using the Bay.

An American-ringed Ruddy Turnstone foraging. Photo by Ruth Walker 

This year, 362 Red Knot were caught, along with 284 Ruddy Turnstone, 75 Sanderling, 407 Semi-palmated Sandpipers, 472 Dunlin and 78 Short-billed Dowitchers. It was very pleasing to see that of the Red Knot ringed during the final catch of the season, 74% weighed more than 180g, 23% were over 200g with the heaviest bird weighing in at a whopping 228.6g! Thankfully, only 4% weighed less than 150g and would need to remain for longer in the Bay.

As the birds departed the Bay, so did the BTO staff and other volunteers. We look forward to catching up with the birds again next year! 

16 June 2015

Buzzard nest with a difference

We were contacted recently by Sam Bayley with the following fascinating story:

Early June marks the time when I check out a few of the many raptor nests that are present in my local area. After discovering three active Buzzard nests and a Kestrel nest I got a small team together including the invaluable help of tree climbers Max Varney and Sam Baker. The first two Buzzard nests and the Kestrel nest were very straightforward with broods of one and two Buzzards and a good brood of five Kestrels, but the third Buzzard nest at South Holmwood was something entirely different!

I had ringed this nest in 2014 when it contained three chicks and it was very typical with lots of evidence of rabbit unsurprisingly being the main food supply. It was very evident even from the base of the tree that this year was different, with a scattering of feathers on the ground below the nest. On reaching the nest Max and Sam found two Buzzard chicks and an unhatched egg surrounded by the remains of various species of bird. Buzzards will take birds, but only occasionally as they aren’t particularly adept at catching them and when they do it is usually limited to chicks or newly fledged birds. The species identifiable were Stock Dove (adult), Jackdaw (adult and nestling), Jay (newly fledged), Moorhen (adult), Great-spotted Woodpecker (adult) and a single Rabbit bone! It looked more like the contents of a Goshawk nest rather than a Buzzard’s, but obviously this pair had become incredibly proficient at catching these birds.

The two Buzzard chicks. Photo by Max Varney

If that wasn’t unusual enough, Max and Sam could hear another bird calling from the nest and eventually realised that it was a Jackdaw chick which was in its own nest within the structure of the Buzzard nest! The adult Jackdaws had created a tunnel into the side of the nest with a chamber at the end, less than 30cm below the cup of the nest! The Jackdaw chick was much younger than its Buzzard counterparts, so I can only assume that the Jackdaws started nesting after the Buzzards were already in residence. 

The entrance to the Jackdaw nest. The two Buzzard chicks
are just visible in the top of the nest. Photo by Max Varney

The Jackdaw chick. Photo by Sam Bayley

Only an end of nesting visit will tell whether they all survive!

15 May 2015

Old friends welcome in the new CES season

We recently received the following fascinating account of the first CES visit of the year at Foxglove Covert, Catterick, Yorkshire. The first CES visit period of 2015 is now over and we are already hearing stories of how long-term ringing projects can help us learn more about the productivity, abundance and survival of birds in Britain & Ireland.

Tony Crease writes:

The weather plays a major part in any CES day and the start of the season this year was looking as ominous as ever, so much so that juggling the days of the Bank Holiday became an inevitability. With a CES of ten and a half hours, a day of virtual calm is essential.

Monday provided the window of opportunity and 12 ringers from the Swaledale Group turned out for visit 1 of our 23rd CES season. With trees still without leaves after the recent very cold weather, the usually lush habitat was less than ideal for hiding the nets. Nevertheless, we had an interesting day catching 204 birds of 25 species. The first Blackcap and Garden Warbler of the year were processed as well as 29 Bullfinches, 23 Willow Warblers and many of our routinely resident species. What was entirely unexpected was the age structure of the birds, some of which we find are surprisingly long lived.

An incredible 29 Bullfinches were ringed during the session! Photo: John Harding

Among the more common species we processed was a four year old Chiffchaff, Chaffinches that were four and six years old respectively and six Blue Tits from four to eight years old. Even more fascinating was a pair of Willow Tits; the female, who had a large brood patch, had been ringed on the reserve as a juvenile on 9 August 2007 and had been caught every year since – a total of 37 times in all!

As if that wasn't compensation enough for our very early start, to our complete amazement there then followed R084872, a Marsh Tit which had been ringed as a juvenile in the reserve on 10 July 2004. This bird, we believe, must now hold the British & Irish longevity record for that species*; it has been re-trapped 42 times and has been recorded at Foxglove Covert every year since except 2010 and 2013.

The red-listed Marsh Tit is a regular visitor to Foxglove Covert CE site.
Photo by Tom Wallis

Increasingly, we are finding more results like these with several passerines, including Blackbirds, quite often living five years or more. It is a compelling aspect of our ringing activities and one that has improved so much with the introduction of IPMR. We load the birds as we ring them so information on original ringing data is readily available.

While visiting our Tawny Owl boxes recently we found one bird that had been breeding in the same next box for 16 years. It is an intriguing subject and one that continually delivers surprises. Life is full of the unexpected and our feathered friends in and around Catterick provide many thought-provoking examples.

* Note from the editors - the online longevity records will be updated in June / July to include data from 2014. Until then, we are unable to confirm whether this is a new record for this species. Watch this space...

11 May 2015

Exemplary patch working

Local birder Lee Collins writes:

Dawlish Warren is a 1½ mile long sand spit at the mouth of the River Exe in south Devon and is an important roost site for thousands of wintering and passage waterbirds of the Exe Estuary SPA. It has an impressive list of rare vagrants that include- Long-billed Murrelet, Elegant Tern, Short-toed Eagle and Semi-palmated Plover.

However, the patch-workers on site aren't confined to purely finding rare birds; with the benefit of a well positioned hide a dedicated band of regular recorders at Dawlish Warren submit to the BTO and county recorders in excess of 7,000 counts per annum and have developed a growing interest in finding and recording ringed birds in the field. 

With no current ringing on site, all recoveries from recent years have been achieved only by using our optics and a keen eye. In 2014 alone the recording group amassed an incredible 398 reads of 192 individuals, something few sites in the whole of the UK can match.

Recent observations have yielded some important and interesting recoveries with birds ringed from 24 different countries, including Ghana, Mauritania, Greenland, Iceland and Russia, whilst others have had a well-travelled history taking in Namibia and South Africa. 

Common Tern, Dawlish Warren, 29th Aug 2014, darvic ringed at Saltholme, Lee Collins

Notable finds include the first Devon recovery of Little Tern (from Dublin) and the first live Roseate Tern (from Coquet Island, off Northumberland). Common Tern (Saltholme in Teeside & Dublin) and Grey Plover (from Spain & Norway), although common species, hadn't had a Devon recovery in 25 and 50 years respectively. Both the Grey Plovers are notable as being the first Spanish & Norwegian controls of this species in Britain or Ireland, a feat the Recording Group also achieved for a Spanish Spoonbill.

Colour-ringed ‘Sanderblings’ as they've now become known are also a definite highlight and we've recorded 18 in just a few short years. Most have been from ringing schemes from their breeding grounds in Greenland and wintering grounds in West Africa (Ghana & Mauritania), with one of our recoveries also observed in Namibia. This species certainly has a breath-taking migratory pattern.

Sanderling, Dawlish Warren, 20th Jul 2009, Ghanian ringed, Lee Collins

The results of reading rings in the field has also established useful site fidelity and longevity data, in wintering species such as Brent Geese, Shelduck and more specifically Oystercatchers, with five of our Oystercatcher reads being individuals 24 years old or older. One faithful Great Black-backed Gull, from south Cornwall, has to date been read 49 times over a 31 month period on site and another Great Black-backed Gull was seven months from beating the oldest one on record (our Great Black-backed Gull was ringed on the Channel Islands in 1990. Another great gull sighting was the first Lituanian ringed Herring Gull in the UK as well (below).

Herring Gull (Argentatus), Dawlish Warren, 31st Dec 2014, Lithuanian ringed, Lee Collins

Since May 2004, the Dawlish Warren website has been updated daily with latest bird and wildlife news and regularly carries news on the latest recoveries. Annual reports (2013 & 2014) on Warren ring recoveries are available for 2013 and 2014 in pdf format.

Ringed Plover, Dawlish Warren, 4th Oct 2014, Norwegian ringed, Lee Collins

It’s very much hoped that our hard work and dedication in finding and documenting such records can rub off on others, as such endeavours serve a useful cause and can be extremely rewarding.

We’d also like to thank the BTO and various ringers for their invaluable help over the last few years.

27 April 2015

RAS double century

The Retrapping Adults for Survival (RAS) scheme was established in 1998 and uses bird ringing to monitor survival rates of a range of bird species. Coverage is particularly aimed at species which, due to their behaviour or the habitats they occupy, are not often caught by standard mist netting activities in woodland, wetland or scrub, such as Swallows, Dippers, Pied Flycatchers and many seabirds and raptors.

With the RAS season already underway for many species, registrations for new projects have been arriving thick and fast here at BTO HQ. At the time of writing, a fantastic 19 new projects, covering 16 species, have registered to start in 2015. A milestone was reached a few days ago with the registration of a new Tree Sparrow project in Cleveland which became the 200th active RAS project.

Tree Sparrows are a species of high conservation concern due to a spectacular crash in numbers of breeding birds between the late 1970s and early 1990s. Whilst BBS data suggest a significant increase in numbers since 1994, maps from the latest Bird Atlas show breeding Tree Sparrows as being absent from much of the south and west of the country and also declining in abundance south of the Midlands.

Maps reproduced from Bird Atlas 2007–11, which is a joint project between, BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club. Map reproduced with permission from the British Trust for Ornithology.

Tree Sparrow is one of the RAS target species identified in the demographic targeting strategy. Currently, only one project, a study in Durham, has been running for long enough to contribute to the RAS survival trend, and the results suggest that, on average, about half of all adult Tree Sparrows breeding in 2015 will still be alive in 2016. But is this the case at other sites across Britain & Ireland? With two new RAS projects starting in 2015, the total number of active studies will increase to six, giving a much better idea of the national picture.

One project currently contributes to the national survival rate trend for Tree Sparrow (solid line), which shows that around half of the birds alive in one year currently survive to the next; the quality of the trend is considered to be 'uncertain' as the errors (dotted lines around the solid line) are relatively large – addition of more projects will help to reduce the size of these errors. 

There have been recent increases in the number of projects for Mute Swan (now three active projects), Starling (now 10 active and five historical projects), Swift (now three active and two historical projects) and House Sparrow (now 21 active and 12 historical projects) which is fantastic. It would also be beneficial to have a few more projects on species such as Tawny Owl, Barn Owl and House Martin to allow us to produce more accurate trends for these species.

It is rare for all active projects to run in a given year and there are always a few projects that have to end for one reason or another. That said, with more projects still registering for 2015, it would represent an incredible effort if the number that submit data this year hits the 200 mark for the first time.

A massive thank you to all current, past and soon-to-be RAS ringers for their tremendous efforts. Keep an eye on the website for the 2014 results which will be published soon.