Ian Newton Interview
Ian Newton on the mass die-offs of birds in the US, the hazards birds encounter on migration and effects of climate change on bird populations
Ian Newton (photo above, Israel Dec. 2009) is author of the benchmark work “The Migration ecology of Birds” (Academic Press, London 2008). His 27-year study of a Eurasian Sparrowhawk population nesting in Scotland is considered as the most detailed and longest-running study of any population of birds of prey. Ian has been Senior Ornithologist at the United Kingdom’s Natural Environment Research Council. He also has been Chairman of the Council of the Royal Society for the Protection of Birds, President of the British Ornithologists’ Union and the British Ecological Society.
Interview by Thomas Krumenacker, Berlin
5000 dead birds were discovered on New Year’s Day in the small town of Beebe, Arkansas. Similar findings on a smaller scale were reported from other places in the United States and Europe. Does the theory that the birds were scared by fireworks and flushed into buildings where they suffered from collision trauma sound plausible to you?
The trauma theory would make sense. I do not know what the weather was at that time but if there was very poor visibility, if there was mist or if it was snowing and the birds couldn’t see they could easily be attracted to lights and fly into buildings or even hit the ground under those circumstances. So yes, that could have been a major cause of that mortality.
Were you surprised by the media-echo to this incident?
May it be that the lack of hard political news in the holiday season around New Year's day lead to the world-wide coverage of the news as media were desperate for any news?
Exactly, and something that is an unexplained mortality is always a good story because it raises suspicion that something is happening on earth that we don’t know about.
How unusual do you consider such incidents? 5000 birds in Arkansas seems like a lot of dead birds, but perhaps it isn’t?
The problem with these incidents is that they are very difficult to record until they occur in an area inhabited by people. As you know on migration a lot of birds die at sea and we can seldom record those. So it is very difficult to say how frequent these mass-mortality events are. Somewhere in the world there are at least two or three cases of nocturnal weather-induced mass-mortality events on record per decade. These are the ones that reach the scientific literature. And there must be others that don’t reach the scientific literature. I wouldn’t be surprised if there is an average of one or more cases per year like this that just never come to light. If you include causes like parasites, botulisms etc. that would greatly increase the number.
Migrating birds meet multiple hazards – you describe them impressively in your book “The migration Ecology of Birds” – Do you consider weather-related events the most significant natural threats to migrating birds?
Whenever birds are flying, whether on migration or at other times, if they reach an area of poor visibility, which may be a result of mist or fog or it could be a snow blizzard, where they can’t see, their natural reaction is to fly down, to lower, so they can see the ground. And when flying at night if there is any light available they are attracted to those lights. I think the weather, in terms of visibility, makes a large contribution to these events. If the weather was not bad and it was a clear sky they would probably be flying higher and escape all the obstacles that cause the crashes. A lot of birds fly into buildings, towers and similar structures in these conditions. There are a lot of cases of birds flying into communication towers like radio masts. They are almost all either on very dark nights, misty nights or other conditions of poor visibility. They just crash into them and die. There must be many cases each year in the North Sea where birds are flying into oil or gas terminals under these conditions.
In your book you mention one incident where no less than 1.5 million Lapland Buntings (Calcarius lapponicus) were killed in snow-storms in March 1904 in Minnesota and Iowa.
Not an entire species but it can cause heavy mortality from time to time. Of course populations affected to a level like the Lapland Bunting case could take several years to recover but I have never heard that they killed a large proportion of a rare species. But of course that is possible. An example might be the Whooping Crane which is a very rare bird in North America. If they had an event like this, that could drastically reduce the population and it could take another 50 years or so to recover. It would be a much more serious problem if it affected a large proportion of a rare species. Particularly a bird like a crane, for example, which has a very low reproductive rate so it could take years and years before the species recovered again. However, I don’t know of any examples in the scientific literature of that having happened but it is certainly a possibility.
Yes, absolutely. You have to remember that only a century ago the birds had the skies to themselves. Nowadays, however, we have aeroplanes which occasionally collide with birds, as we know, and we also have very many tall buildings and masts plus we now have wind-turbines being built across large tracts of the land and even in shallow water areas. All of these could provide potential hazards for flying birds particularly at night and other conditions of poor visibility. The threats to birds because of human infrastructure and human activity is increasing all the time so I would expect that these incidents can only increase with time.
J.E. Moreau states in his standard book “The Palearctic-African bird migration systems” that only about 50 percent of migrating birds survive migration and return to their breeding grounds. Do you consider these figures appropriate?
Yes, because he was talking about the migration of small passerines and even the resident species have an average of about 50 percent mortality every year. This is not surprising when you think that small birds can double or triple their numbers during the course of a single breeding season. So if the numbers are to stay stable over the long term 50 percent or more have to die from one year to the next. It is not unusual for half of a bird population to disappear between say August of one year and April of the following year. Whether these incidents of human based collision have any impact on the population will depend very much on when they occur during the birds annual cycle. If a lot of birds are killed at the end of summer or in autumn then there is still a lot of opportunity for those losses to be made up during the course of the year, because other mortality maybe reduced then during the winter. But if those losses occur in spring after the winter losses have occurred then obviously the breeding population would be greatly reduced.
This puts a big responsibility on future bird protection measures like staging posts along migration routes back to the breeding grounds, like in Israel and other places where habitat destruction, the pressure from tourism, the omnipresence of cats in huge densities etc. mean serious hazards to birds…
Yes. I think the spring migration is by far the most dangerous because as you have indicated most of the mortality is over by then so the population is almost at its lowest level of the year. If you then cause additional mortality that could have a huge effect on the subsequent breeding population and those effects are much greater and more important in spring than they would be in autumn when the population is large.
What could be the worst consequences of major encroachments at stopover sites?
There is a lot of evidence that the conditions the birds face at stopover sites – and Israel is of course a very important one – can influence the subsequent survival and population sizes of these birds. A very dramatic example from North America is concerning Knots Calidris canutus. The last major stopover for Knots in North America in spring is the Delaware Bay in New Jersey. Whilst there they live mainly off the eggs of Horseshoe crabs on which they fatten before they migrate several thousand kilometres directly to the Arctic. But in recent years that crab-population has declined as a result of human over-fishing so the food supply for the birds has declined drastically. And that has resulted in Knots being unable to accumulate sufficient body fat on migration to return to breeding areas and then breed. The mortality rate in these birds increased by about 37 percent within the space of two years. The reproductive rate fell about 47 percent and the population halved in a two-year-period. And that was attributed entirely to events at a single major stopover site. Probably the most important stopover site but individual birds were only there for ten to 14 days and events in that short period at that crucial site were sufficient to cause a halving of the population within the space of two years. This is the most dramatic example of conditions on migration I know.
This is an impressive example of a very obvious man made encroachment into nature. Let’s talk about other, more indirect human influences like climate change with an increase in unusual weather events etc.
We know from the past that severe storms can kill large numbers of birds on migration during one night in a particular area. If these storms are going to increase in frequency through climate change we can only expect that they will have even more frequent and dramatic effects on bird populations.
Combining all these hazards, natural and man made, in the long term will there still be a place for such a fantastic phenomenon like bird migration on our planet?
I hope so very much indeed. We are conscious of these problems and we are in a position to do something about them - like with the Knot example - and as I mentioned earlier, wind farms and other large obstacles and their siting.
Wind farms are a major challenge. They must be situated where they are least likely to damage large numbers of birds. The major worry is that we don’t have enough information on the impact of these wind turbines so it’s very difficult to argue against them. One of my main worries is that a lot of wind turbines are built in the shallow waters of the North Sea off the East coast of Britain and that’s on a direct migration route of birds from Scandinavia and Europe who winter in Britain. They now face a whole barrier of large wind turbines. In good weather they probably migrate straight over and there is no impact but on misty weather they are flying low and this could cause large mortalities.
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