What makes for a long life?

Rob Robinson writes:

I am sometimes asked the question: “How long do birds live?” The answer is, as to many good

questions, “It depends”.

The oldest known wild bird is a Laysan Albatross called Wisdom who breeds on the very remote Midway Atoll in the Pacific Ocean and is around 70 years old. The oldest known bird in Britain is a Manx Shearwater from the island of Bardsey in north Wales that was over 50 years old when last seen back in 2008 (more on that in a bit). The reason we know this, of course, is because both of  these birds have been ringed, so we can follow them as individuals. In fact our shearwater outlasted both the original ring and its replacement, so was on its third ring when last caught!

Manx Shearwater. Photo by Lee Barber

Not all birds live so long, clearly; the longest-lived Blue Tit, by comparison, was last seen a few months short of his 10th hatchday. The graph below shows the longevity for each species ringed in Britain and Ireland. But measuring longevity in this way is tricky; to get an accurate figure we  generally) have to catch the bird to fit a ring in the year it was hatched, and then the individual has to be found shortly after it, sadly, dies (these are marked by squares in the figure). This happens rather rarely – Carrion Crow (at 21 years) is one example, but you can see there are relatively few other squares on the graph. More commonly, we catch the bird as an adult so don’t know when it was hatched (the downward-pointing triangles), or the individual is caught/seen before it dies (the upward-pointing triangles), or, sometimes, both (the diamonds on the graph). So the Manx Shearwater was first caught in 1957 as an adult (so at least five years old already, possibly more) and then seen every few years until its last capture in 2008, but we don’t know when it died; we only ‘knew’ it for part of its life.

The oldest ever Manx Shearwater, then, is (was or will be) certainly in their late 50s and possibly into their 60s. This highlights another issue with longevities, these individuals are, by their very nature, exceptional, and so few and far between (think how many people live beyond 100, for example). We also have to wait, sometimes for many years, before we can get a fair estimate. Goosander on the graph is a good example: we know the age of HW37685 fairly well, he was ringed as a nestling, and we know when he died (aged 9 ½), but only 10 or 20 goosanders are ringed each year, so the chances of someone ringing (and then finding) the oldest, or even close to the oldest, bird are pretty slim.

Fortunately, we have a better way of measuring longevity, through a measure known as annual survival, which is simply the proportion of individuals that make it from one year to the next; it is the flip-side of mortality. As the graph shows, and one should expect, there is a strong relationship between annual survival and overall longevity.

Species that tend to live longer have higher annual survival rates. Points are coloured by body size and the shape indicates whether the longevity of the individual is fully known. Squares represent a bird ringed as a nestling/juvenile and subsequently found dead. Pointed shapes indicate uncertainty in age, either at the beginning (downward-pointing) or end (upward-pointing) of the bird’s life.

While a few Blue Tits can live as long as 10 years, most do not. In fact, our ringing data show that the annual survival rate of an adult is 0.53. This means that for every 100 adult Blue Tits starting the year, 53 will make it to the end or, conversely, that 47 of them will die at some point during the year. It is worth just stopping for a second and reflecting on what this means out there in our gardens and woods. At last count, there were approximately 3.4 million breeding pairs of Blue Tits in Britain, so 7 million individuals, near enough. A survival rate of 0.53 implies that, in the normal course of things, around 9,000 Blue Tits die, on average, each day (7 million * 0.47 / 365); that’s about three in each and every 10 km square every day. Adding in young birds will, of course, make this figure much higher in the summer. The balance of productivity and survival is important then, since each of these birds needs to be ‘replaced’ if the population is to remain stable in size.

An alternative way of expressing survival is life-expectancy. In the Scottish play, Shakespeare reckoned on living “threescore and ten”, i.e. 70 years (a figure that, in fact, dates back to biblical times, although recently is more like 80 years in developed western countries but nearer 50 years in countries like Afghanistan and Somalia). Broadly, life expectancy in birds varies by size - heavier birds, marked by darker colours, fall more on the right side of the graph, lighter birds, in both colour and mass, to the left. Most small birds, like the Goldcrest, that fledge will not survive to breed. That is, their life-expectancy is less than one year; being a young bird is hazardous indeed! At the other end of the scale, Mute Swan cygnets have a reasonable expectation of making it into their early teens.

The graph shows how most birds cluster about an average line; as survival increases so does the recorded longevity. (The line curves sharply upwards on the right simply because, numerically, survival cannot be greater than 1.) Species that fall well below the line (like Lesser Spotted Woodpecker and Capercaillie) are ringed in such small numbers that we simply don’t have a good estimate of their total longevity yet; in future years these points should rise to become closer to the line. All the conservation effort that has been put into looking after Red Kites, probably means the longevity of that species is a bit higher than it might have otherwise have been. For Wigeon, on the other hand, the annual survival is much lower than we might expect from their longevity because they are hunted over much of their range, the point is well to the left of where it might otherwise be. This leads us on to the main reason why knowing about survival rates is interesting, and why ringing individuals is such a powerful tool.

By measuring how survival varies in different places or times we can understand how and why populations change. By and large, adult survival usually does not vary very much – we find it is pretty consistent between places and over time. When it does change though, the effects can be dramatic. The decline of the Lapwing (see figure) was caused, in large part, by a run of cold winters that made it hard for birds to find food. The population hasn’t recovered, though, not because survival rates have stayed low (they bounced back), but rather because the number of chicks that can be produced in Britain’s intensively managed landscapes was too low to replace those that succumbed. Similarly, the population of Oystercatchers on the Wash (and elsewhere) is sensitive to reduced survival caused by over-harvesting of cockles and mussels, a fact which is now taken into account in managing the shellfisheries there. More often though, it is the balance of survival and productivity that is key, as we see in the decline of Willow Warblers in England and understanding this balance is key to designing effective conservation measures.

Survival of lapwing (purple dots, with 95% confidence limits) was reduced during a period with cold winters (blue arrows) causing a decline in the breeding population (green line, shading indicates 95% limits) in the 1980s. Redrawn from Robinson et al. (2014).

So. What does make for a long life? Certainly if you are a bird being larger helps, and the ringing report shows that all the longest-lived birds are seabirds. But what I hope I have shown is that while the longest-lived individuals are interesting, ringing tells us more about how well the average individual does, and this is why the efforts of ringers are still important. Although tracking studies are producing fascinating new insights virtually every week, the number of birds tagged (or likely to be tagged in the near future) will generally not be sufficient to help us measure survival of birds across the population. Ringing remains the only way to do this, and will continue to be a vital tool in understanding and managing our bird populations for years to come.

If you find a dead bird with a ring on, even one that has hit a window or been brought in by your cat, then you too can contribute to our monitoring of survival. Please tell us by filling out the details at www.ring.ac. There is more information on where birds go, what happens to them and how many birds are ringed in each county on our online ringing and nest recording reports.

Who gives a hoot

Occurring throughout England, Scotland and Wales the Tawny Owl is well known, especially during the winter when their territorial calls can be heard during the night.

The Tawny Owl is amber listed, i.e. a species of medium conservation concern due to recent population declines. Surveying this species can be difficult, but studying them is easier due to their readiness to use nestboxes. Ringing the adults and their chicks, as well as following the progression of the nesting attempt (nest record), provides very useful information to help interpret population changes.
 


Adult Tawny Owl. Photo by Rachael Barber



Adult Tawny Owl with a more grey plumage. Photo by Lee Barber

The number of Tawny Owls ringed each year varies considerably; in the last five years the number ringed has ranged from 920 to 2,748 birds. The number ringed also varies by county, with ringers in Northumberland topping the list with an average of 183 birds per year. This is followed by Lincolnshire (107), North Yorkshire (100), Nottinghamshire (92), Norfolk (81) and Cumbria (81). Around 80% of the birds ringed each year are chicks. Ringing chicks enables researchers to follow an individual throughout its lifetime, providing vital information on where birds move to and exactly how long they live.


Tawny Owl chicks. Photo by Lee Barber

For most of the recoveries the BTO receive, the cause of death is unknown, but for some the cause of death is clear. Being hit by a vehicle is the most reported cause of death for Tawny Owls, followed by train casualty and drowning in artificial water containers like horse or cattle troughs. This doesn’t mean that 66% of all Tawny Owls die from vehicle strikes, however. Birds killed by vehicles are inevitably more visible than a bird that dies of natural causes in the middle of a wood. Also, as most of the birds that are reported are from areas with high concentrations of people, these are more likely to be reported when found.

By recapturing ringed birds, licenced bird ringers are in the privileged position to be able to gather information on the presence and condition of Tawny Owls that are alive and well. Last year one of our ringers re-caught a Tawny Owl that was originally ringed as long ago as 2003. This bird was ringed as a chick and re-caught in the same place (Kielder Forest, Northumberland), so the exact age of this bird is known (13 years). A bird ringed in 2004 at Rowlands Gill in Tyne and Wear which was also caught during 2016, that was an adult (at least 1 year old) so she could have been much older. It would have been doing very well to break the longevity record of 21 years 10 months.

Unlike some other owl species, Tawny Owls doesn’t generally travel very far or cross large bodies of water, so their distribution is restricted to mainland Britain.  Due to this behaviour we have had no foreign recoveries in the history of the BTO Ringing Scheme.


Tawny Owl chick about to be ringed. Photo by Lee Barber

I have received one recovery while working at the BTO, of a ring found in Iceland (without a bird) which was originally put on a Tawny Owl chick. This was an amazing record so (as with all our recoveries) some investigation followed. Unfortunately, this wasn’t quite as amazing as we’d hoped as we had a previous record that this bird had already died. The ‘used’ ring was put on a binocular strap for safe keeping after reporting. Some years later the finder was on holiday in Iceland when the strap broke and the ring was lost, only to be found later by someone else who reported it to the BTO via www.ring.ac.

The vast majority of data from ringing and the resulting finding of dead birds can provide an amazing amount of information, so if you do find a ringed bird please report it via www.ring.ac.  As a thank you, you will receive the information on where and when the bird was ringed.

Elderly Shag strengthens our position in Europe!

Jim Lennon from the Shiants Auk Ringing Group writes:

Ringing seabirds can be mucky and challenging work, especially when you’re ducking under a rock to reach a Shag chick, while keeping an eye out for its protective parents (often the croaking male). However, this is soon forgotten when you receive news of one of them nearly 31 years later!

Shag chick 1227282 was one of a brood of three ringed on the Shiants Isles, Western Isles, on 30 June 1985 by Ms Sam Powell, a trainee ringer from South Wales working with the Shiants Auk Ringing Group. A total of 725 pulli from 377 broods was ringed on the Shiants that year.  Most of the subsequent recoveries were of birds that perished within the first 12 months, a few survived for four or five years and an exceptional bird was found dead after nine years.

But 1227282 outlived them all by a country mile.  For the next 30 years following ringing, it most likely spent its life breeding on the Shiants and in the waters of West Scotland, but we’ll never know for sure as it was never heard of again until John Taynton, a RSPB worker on the Shiants, found it freshly dead on 26 April 2016 i.e. a life span of 30 years 302 days.

According to the BTO’s latest longevity list (2014), this makes the Shiants bird the oldest ringed Shag in Britain & Ireland, and also in Europe (see Euring), raising the record by nearly a year.

Note:
The Euring information is not updated as regularly as the BTOs longevity lists because it needs to access all the data from all the Euring ringing schemes and this can take some time.  It currently indicates that a 34 yr old bird from the Shiants is Europe's oldest  Puffin but two just shy of 36 years old and one almost 37 years old, are listed on the BTO longevity records site.

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...

Great Spotted Woodpecker reaches a Great age

Since 1909, ringing has occurred on these islands and with all this information, a great deal has been learnt about how long wild birds live.

The BTO has compiled a longevity list that is updated annually here, which includes the details of the oldest British and Irish birds wearing a BTO ring. At 3 years 2 months, the Firecrest burns out quite quickly, to the other end of the spectrum of the 50-year old Manx Shearwater.

Longevity records are beaten relatively rarely so it's a special occasion when a ringer re-catches a record breaking bird, unless it's a recently colonised bird like a Little Egret (9 years 6 months) or Egyptian Goose (12 years 5 months).

Female Great Spotted Woodpecker

The last longevity record for a Great Spotted Woodpecker was set in 1976 with a bird caught in Rochester, Kent. That has now changed with Alan Ball contacting us about a 10 year, 10 month and 30 day, female woodpecker at Bourne Wood, Lincolnshire!

The wing of a definite adult Great Spotted Woodpecker with retained primary covert

This year has also produced several old Blue Tits in Bourne Wood including one 7 years 11 months and one 7 years 10 months and another aged 7 years. Just a couple more years to break these records as well.

Thanks to Alan for letting us know and for the photographs. The online longevity pages will show his record once we have all the data in for this year.

The History of One Med Gull and Three Rings

Luke Phillips, who works for the RSPB, told us last week about a Mediterranean Gull that is visiting Radipole Lake RSPB Reserve 18 years after it was first caught for ringing in The Netherlands.

According to the ringing database, this would be the longevity record for Mediterranean Gull recorded in the UK, but not as old as the longevity record for Europe, which was a Med Gull ringed by the Greek Ringing Scheme and recorded 22 years and 1 month later.

Many Mediterranean Gulls are ringed and colour ringed in the Continent, but only a few dozen are ringed in the UK each year. In 2010 only 22 birds were ringed with a GBT ring, contrasting with the 618 ringed birds that were recovered/resighted during the same year. The number of birds wintering and breeding in this country is increasing, and this trend is expected to continue in the future.

The travels of this Mediterranean Gull are very well documented, its life history spanned 6 pages!

In summary:

It was ringed in The Netherlands as a pullus and was given colour ring WHITE 96A on 02/06/1993.

It was caught again in Belgium in 1999, the metal ring was replaced and the colour ring had been. In 2006 was caught again in Belgium, the metal ring replaced and a WHITE 3K20 added.

As 3K20,it was seen on 06/12/2011 in the UK for the first time at Radipole Lake where up to 450 Med Gulls were recorded in a single evening by Luke Phillips.

The colour ringing of Mediterranean Gulls is well coordinated in Europe and sightings can be reported here.

To find out more about longevity records in the UK go to the on line ringing reports, and for European longevity records go here.

Thanks to Luke Phillips for telling us about this gull and to Chris Parnell for both finding the bird and for providing the photograph.