In 1803 John James Audubon tied a piece of coloured yarn around the leg of a small songbird called the phoebe. His reason? To find out whether the migrating birds returned to the same breeding site each year. He found this to be the case. He also used this experiment to monitor their feeding habits. His efforts have been sighted as the first-time banding has been used to study birds.
Today, banding, or ringing, birds is commonly used to track their progress. And it’s not just birds that are tracked; these days’ scientists are keeping tabs on everything from bees and butterflies to whale sharks and elephants. The tools at their disposal range from plastic and metal rings – things have moved on since Audubon used yarn – to highly sophisticated GPS/GSM tracking devises.
Tracking plays a significant role in conservation. Not only does it help us understand their movements, behaviour, feeding and breeding patterns, it informs us what impact weather patterns, natural disasters, man-made disasters, human activities and so much more are having on our wildlife. Without this understanding, it would not be possible to protect the natural world and the species which rely on it; and that includes us.
In this monthly series, we will investigate the different ways scientists undertake their tracking projects, what they have learned and how the information is, or will be, used to inform conservation.
Whilst we will look at tracking of various species and at the different methods used, this month we will bring the Audubon story up-to-date by looking at a long-term bird monitoring project that has used ringing as part of its observations. It is also quite fitting that the bird in question is a relative of the extinct great auk; a species that may have benefited from a bit of tracking!
Monitoring Skomer Island’s guillemots
The common guillemot is by no means a rare auk. In fact, it is one of the most abundant seabirds in the Northern Hemisphere. They have a circumpolar distribution, occurring in the low-arctic and boreal waters of the north Atlantic and north Pacific (del Hoyo et al. 1996) and breed in large numbers on the coastal cliffs of the UK and Ireland. Those which breed on Skomer Island, off the west coast of Wales, have been the subject of a long-term study that started in 1972.
The study, was triggered by the widespread concern in the 1960s that guillemot populations were decreasing. Oiling incidents were common at the time and having a devastating impact on the oceans.
A major natural disaster occurred when the Torrey Canyon tanker sank off the western coast of Cornwall in 1967. The tanker’s cargo of 100,000 tons of crude oil was spilt into the sea, decimating the marine life in the area and resulting in the death of over 30,000 seabirds, most of which were common guillemots.
The unease about the guillemot’s fate intensified when a mass die-off in the Irish Sea in 1969 further reduced their numbers. Whilst severe storms played a part in the die-off, it was discovered that many of the birds had died of starvation. Further investigation found these birds contained very high levels of toxic chemicals known as PCBs or polychlorinated biphenyl (an organic, hydrocarbon chemical) used for various industrial purposes.
By 1970, guillemot numbers had reached an all-time low both on Skomer and elsewhere in the Irish Sea. In 1972 a three-year PhD project, supervised by Chris Perrins and the late David Lack, was set up with the aim of understand the dynamics of the declining population of guillemots on Skomer. Tim Birkhead was to undertake the PhD and is still the project lead to this day.
Success comes from longevity
At this stage, it is worth pointing out that for a large number of wildlife studies success comes from longevity. This is particularly pertinent in this case. Guillemots are long-lived and do not start breeding until they are at least five years old. To understand the population dynamics, requires accurate measures of how long individual adult guillemots live, how many chicks they produce, how old they are when they breed, what proportion of young birds survive to breed and how changes to their environment is affecting them.
The fact that guillemots are relatively common makes it an excellent study species. Its abundance makes it an excellent indicator species. Scientists use indicator species to examine the health of an ecosystem. By measuring their presence and numbers over a period of time, a picture can be built of the health of an ecosystem, any changes to the environmental conditions and how this is impacting the biodiversity in the area.
Using colour rings
There were two key questions Tim needed to answer during this project:
- how long do guillemots live? And
- how old are they when they first start to breed?
To find the answers, Tim used colour rings. These days, there is no need to rely on pieces of coloured yarn. The rings are made from durable acrylic, come in a variety of shapes and sizes, and are custom made by specialists. Some of the rings, as in Tim’s project, contain numbers that can be read at a distance through a telescope.
To find out the average life-span of the guillemot, required to understand the population dynamics, a couple of hundred birds were colour ringed. By using numbered rings, individual birds could be recognised. Guillemots tend to return to breed on the exact same position on the cliff year after year. The team use the rings to identify which birds make this return and can therefore work out how many birds have survived from one season to the next. Using this data, the average lifespan can be estimated. In this case the average breeding lifespan was estimated to be around 20 years. It was also found that some of Skomer’s guillemots can live for over thirty years.
Colour ringing was also used to determine how old guillemots are when they first start to breed. In this instance a large number of chicks were ringed and then were monitored year-on-year until they started breeding. The results showed that average age of first breeding was seven-year-old. This is the average age; the earliest breeding attempt was recorded after three years, whilst others were over ten-year-old when they started.
Using colour rings does have its challenges. Catching and ringing birds that spend most of their time either on cliffs or out at sea is not the simplest of tasks. Also, due the high density of birds in the breeding colony, it is not easy to get a good view of their legs. Time and patience is certainly a prerequisite for this project.
Long-term monitoring – a vital tool
As well as answering the questions above this project has provided a significant amount of knowledge about the guillemot; such as:
- The birds now breed two weeks earlier than they did in the 1970s, probably as a result of climate change.
- Around 70% to 80% of pairs on Skomer successfully manage to rear their chick (guillemots only lay one egg) to fledging age.
- Fledging in guillemots constitutes them jumping off the breeding cliff at 21 days old into the sea below. They are still unable to fly and will still be cared for on the sea by a parent; usually the male.
- Guillemot numbers on Skomer Island have increased steadily at about 5%/year since the 1980s.
- The Skomer population in 2015 was approximately 20,000 pairs; a healthy total but considering the estimation for the 1930’s was 100,000, there is no room for complacency.
Over 20,000 hours of fieldwork have been invested into this project, with many more spent analysing data after the breeding season. In excess of 13,000 birds have been colour ringed. Much has been learnt and has yet to be. In the 2014 storms 40,000 seabirds perished. Thankfully, the impact on the Skomer guillemot colony was not too significant. We only know this because of this project. Climate change is expected to increase the frequency of such storms, so to understand the impact of global warming on ecosystems, we need to analyse the long-term biological impact of these events.
Long-term monitoring is a vital tool for tracking the health of our wildlife and informing future conservation efforts.
Support this project: Thanks to short-sighted Welsh Government’s decision regarding funding, this project has been forced to turn to ‘Just Giving’ to raise necessary funds. Without this help, the project would have ceased in 2014. If you would like to help, donate at Just Giving.
With thanks to Tim Birkhead for his support in writing this article.
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