German KP update

In the past the majority of recoveries received at the BTO concerned reports of dead birds, so reports where live birds were reported were few and far between. With the advent of colour ringing, particularly of raptors, waders and gulls, the chance of getting reports which track the movements of birds has greatly increased. 

Kentish Plover taken by Martin Casemore

We posted in March about a Kentish Plover that was ringed in Germany as a breeding adult at St Peter-Ording (Schleswig-Holstein, Germany) in May 2009 (red pin). It returned to the same site again in June 2010, and was then seen in Sussex in March 2013 (yellow pin). This is valuable information in itself but it has now been reported on 24 June 2013 on the Eider Estuary (blue pin), Schleswig Holstein, Germany.


View Kentish Plover in a larger map

We still don't have much information regarding KPs that visit the UK or Ireland, so this information is very interesting. Hopefully we'll get to see this bird once again on our shores.

Thanks to Dominic Cimiotti for letting us know.

Trichomonosis insight

The impact that diseases have on bird populations is a fascinating topic of research, to which ringers and members of the public can contribute. Many will now be aware of the detrimental effect that Trichomonosis has had on Greenfinch populations in the UK, a relationship established by a piece of research led by scientists at the Institute of Zoology in London and the BTO. A subsequent study from the same team also showed, through molecular analyses, that the disease arrived in Fennoscandia from the UK in 2008, most likely carried by Chaffinches. This link was identified thanks to the known migration route of this species provided by previous ringing data.

Greenfinch showing signs of Trichomonosis by Heather Povey

A project by different authors has recently showed that Trichomonosis spread in Finland in 2008 and 2009 and impacted local Greenfinch and Chaffinch breeding populations. In August-September 2008 the first cases of this disease had appeared in the country, followed by a peak in reported mortality in July 2009, although cases diminished in 2010 to pick up again in 2011. The Finnish study showed that population of breeding Greenfinch declined by 47% in south Finland, but not other parts of the country, at the peak of the outbreak between 2009 and 2010, whilst Chaffinch declined by 4%, between 2006 and 2010, the first population decrease since 1984. Bird body condition was also affected by the disease. Ringing data highlighted that Greenfinches, especially juveniles, were lighter than usual over the autumns 2008 and 2009 in the areas most affected by Trichomonosis.

These studies are a very good example of the important contribution to science that members of the public and ringers provide by reporting changes in birds and garden wildlife, as well as the unique high-quality data and essential information that ringing provides.

For more background information, visit the BTO GBW webpage

Daria Dadam, Research Ecologist

Lost Sedge Warbler Czechs in

Considering the hazards of migration and the massive distances involved, it's quite amazing that birds make it back to breeding sites year on year. But just occasionally there's a bird that bucks the trend... One such bird was Sedge Warbler Y931333, originally ringed on migration in Sussex on 1st August 2012. It presumably spent the winter in sub-Saharan Africa, but was recaught on 4th May by ringers at Lázně Bohdaneč in the Czech Republic. When recaught this bird was sexed as a female, so was presumably in breeding condition, so why it was migrating through Sussex in a previous year is a mystery.

The BTO's online ringing report (with the map below) shows that this is actually the furthest east recovery of a British-ringed Sedge Warbler from over 100 years of ringing, beating the previous bird which is the only other British Sedge Warbler to be found in the Czech Republic. Coincidentally, this bird was also ringed at the same site in Sussex, in August 2003!
 

Marsh Tit population crash

The NERC Centre for Ecology & Hydrology (CEH) Marsh Tit project in west Cambridgeshire was outlined in a previous Demog Blog post in 2010, and is now in its 10th year. But after a decade of stability 2012-13 has seen a dramatic fall in the population, and ringing has enabled us to understand how and why this has happened.

Almost all of the Marsh Tits in the main study population are colour-ringed, and the number of territories in the four main study woods has typically been around 30-32 each spring, with about 15% of those being occupied by lone males. But in 2013 the number of occupied territories has fallen by a third to just 19, and more than a quarter of those did not have a female present.

Adult survival from the previous spring was only 44%, which was among the lowest recorded since the study began and some way short of the average 51%, but this alone could not explain the sudden drop in population. The main problem was juvenile recruitment, linked to the very poor weather during the breeding season in May 2012. In line with results for other tits shown by the Nest Record Scheme (click here for 2012 premilinary results), the Marsh Tits also seemed to struggle to rear young during 2012 as persistent rain hampered foraging. Things were so bad that we had the first ever record of adults abandoning a nest mid-way through incubation.

Reduced productivity, and probably also reduced fledgling survival, was apparent in the much reduced number of juveniles recruited into the population during our autumn trapping period, when I catch and colour-ring most of the new birds. During a typical year I expect to find 50-60 juveniles in the four woods between August to October, but in autumn 2012 the number was just 21. With so little recruitment on top of lower than average adult survival, there were not enough juveniles to replace adult mortality and maintain the breeding population in 2013. The gender imbalance in the surviving birds indicated that mortality was especially severe among females, which are at the bottom of the pecking order.

That extreme weather and a single poor breeding season could almost halve our breeding pairs was quite worrying. Marsh Tit is a Red-listed species that has declined nationally by 72% since the 1960s, and our study shows that random events such as the very wet spring 2012 can be a severe blow to fragmented populations of birds that may already be struggling. With 2013 shaping up to be another relatively poor breeding season for tits, the previously large and stable population of Marsh Tits in the Cambridgeshire study may take years to recover, if it ever does.

Thanks to Richard Broughton for writing this post and for the photos.

Tawny having a tough time

The nests of Barn and Tawny Owl have been recorded in Lincolnshire and Nottinghamshire intensively since the mid 1980s. This has provided a wealth of information, which is used to look at many aspects of breeding success.

Adult Tawny Owl by Carol Greig

Adrian Blackburn and Jim Lennon, along with help from other ringers, checked 82 Tawny Owl nest boxes on 21-24 April 2013 in East Lincolnshire, and recorded an occupancy rate of just 17% (14 boxes). Squirrel, Jackdaw, Stock Dove and Great Tit were also recorded. In total in 2013, just 17 chicks were ringed from seven broods; half of these were provided by two surprisingly large broods of four chicks, with and one other containing three young while the remainder were the rest consisted of single nestlings or pairs of owlets. This is much lower than the average number of 36 ringed young recorded over the period 1996-2012 and far below the highest annual total ever, an impressive 62 chicks ringed in 2005.

There were still two nests with eggs on the last visit could potentially produce more chicks but are very unlikely too at this stage; the other five had failed either during incubation or soon after the chicks had hatched.  We posted previously about the hard time Barn Owls were having due to the cold spring, so finding that Tawny Owls were also having a hard time was not a great surprise.

Some reasonably healthy Tawny Owl chicks by Carol Greig

There is evidence of a lack of prey from the boxes with fewer voles and mice being found, these being replaced with more unusual items, including the hind leg of a hare, a Carrion Crow’s head and a few shrews. It is notable that the boxes in ‘prime’ deciduous woodland habitat, which usually produce the majority of offspring, fared worst, with those in suburban gardens achieving a much higher output. Could it be that small mammal populations in woods have become depleted during months of cold weather and poor vegetation growth, while garden rodent populations thrive on the artificial food provided for birds?  The situation is probably not helped by the breeding season for song birds being delayed by several weeks, potentially reducing the availability of young birds as prey.

Thanks to Adrian Blackburn and Jim Lennon for letting us know.