Bold and aggressive behaviour means birds thrive in cities

As readers of this blog will know I studied how birds change their behaviour in cities for my PhD. I pleased to say I recently published part of this work in the journal Scientific Reports. I wrote a piece about this for The Conversation which I reproduce below.


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Great tit takes off.
IURII FEDOROV/Shutterstock

Sam Hardman, Max Planck Institute and Sarah Dalesman, Aberystwyth University

Most people probably wouldn’t consider bustling towns and cities good places for nature to thrive. Yet a few species of birds have so successfully adapted to city living that they boast large and thriving urban populations. Now, research has suggested that the success of these city-dwelling species may lie in their behaviour.

Urban habitats are quite different to the natural environments in which birds evolved. Cities are noisy places, they are lit almost continually with artificial lights and they contain an abundance of food. Cities are also full of people. This means birds living there rarely get any peace and must cope with almost constant disturbance from both humans and their pets.

But birds living in cities are known to be much more tolerant of human disturbance than their rural compatriots. In a study of 44 European bird species, all but four allowed humans to approach them more closely in cities than in rural habitats. This suggests that city birds are bolder in the face of a potential threat.

Parus major: the great tit.
Erni/Shutterstock

It’s not only towards humans that urban birds seem to be bolder. We recently studied the territorial behaviour of male great tits (Parus major) in cities and rural habitats in the UK and found significant differences between them.

During the early spring, males of this species defend breeding territories. Once a male has a good territory he signals his ownership to other birds using song. In fact, together with attracting females, one of the main uses of song is territory defence.

When a rival male enters another’s territory and begins to sing, the territory holder usually responds aggressively to drive the intruder out. At first, this may mean simply singing back, but can quickly escalate to full-on physical conflict.

In our experiment, we used playbacks of great tit song to mimic an intruding male. This allowed us to measure how strongly urban and rural great tits respond to intruders. We found that city birds approached the intruder mimic 35 seconds faster and almost two metres closer than rural birds. This suggests that urban great tits are both bolder and more aggressive than rural great tits.

And it’s not just great tits which are known to be more aggressive in cities. Urban song sparrows (Melospiza melodia) have also been found to be more aggressive towards each other during the breeding season.

Melospiza melodia, or song sparrow.
Elliotte Rusty Harold/Shutterstock

Why urban birds should be bolder and more aggressive than their rural cousins is not yet fully understood. One possibility is that in cities, where space is limited, only the most aggressive individuals are able to hold a territory.

Animal personalities

In addition to researching levels of aggression, we also looked at how consistent males were in their aggressive displays. This consistency in the way animals behave over time is often referred to as “animal personality”.

We found rural great tits were very consistent in the way they behaved towards an intruder over two consecutive days, but urban birds showed lower levels of consistent behaviour. This could be due to the fact that urban males experience greater fluctuation in their environment on a day to day basis.

Urban bird territories are also packed closer together in cities, which means that the birds are likely to cross each others’ paths more often, increasing the chances that squabbles will break out.

The increased likelihood of aggressive encounters may also explain the lack of consistency of urban male behaviour. Animals remember fights they have had and their experience alters the way they behave the next time they encounter an opponent. Urban males are more likely to have had an aggressive encounter with males in their territory, which could then alter the way they behave towards our mimic of an intruder the following day.

As well as aggressive behaviour, being bold may also help birds survive in the city. Bolder birds have been shown to be more willing to explore new environments and to find new types of food to eat. As cities are vastly different to natural habitats, and contain many new types of food, boldness is likely to be a very useful trait for urban birds to have.

The ConversationThe big question which remains for ecologists is whether birds in cities are evolving to suit their new urban environment. A recent study has shown genetic differences between rural and urban great tit populations which suggests this may be the case.

Sam Hardman, Research Assistant, Max Planck Institute and Sarah Dalesman, Lecturer, Aberystwyth University

This article was originally published on The Conversation. Read the original article.

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Lightening fast responses allow birds to cope with urban noise

Animals in urban environments face many unique challenges including finding and adapting to new sources of food, coping with almost continual human disturbance, and learning to avoid introduced predators (domestic cats I’m looking at  you).

Another factor that all animals in urban habitats must learn to cope with is noise. Noise in cities comes primarily from cars and other road vehicles, but is also produced by factories, building sites, roadworks and numerous other human activities. In my own experiments I have measured noise levels in excess of 70 dB next to major city roads. For comparison, that’s as loud as a vacuum cleaner from 3 metres (10 feet) away! Even in quieter areas and at the quietest times of day urban noise rarely dips below 50 dB which is around the same level as in a bustling office.

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Urban habitats are noisy places

For animals in urban environments there is almost no escape from noise. This presents a major problem for species which use sound to communicate as their calls and signals can easily be drowned out and lost in the din of the city. However, as is often the case in nature animals have found a solution to this problem and it is surprisingly simple.

In noisy environments many species, including all mammals and birds so far tested, unconsciously increase the amplitude of their vocal signals to ensure they are heard. This response to noise is known as the Lombard effect, named after its discoverer the French scientist and doctor Étienne Lombard (1869 – 1920).

Etienne Lombard
Etienne Lombard (1869 – 1920). The discoverer of the Lombard effect

Surprisingly however, despite numerous studies of the Lombard effect in many different species very little is known about how quickly the Lombard effect acts after sudden increases in noise. For city dwellers the ability to respond to changes in noise levels quickly may be vital as things such as passing vehicles or sporadic building or road works can cause noise levels can fluctuate wildly over the course of a day. Even in wilderness habitats noise levels can change quickly due to wind, rain or the even the calls of other animals.

Lombard phylogeny birds and mammals
The Lombard effect has been shown in every species of bird and mammal so far tested and across evolutionarily diverse groups. Figure adapted from Brumm and Zollinger (2011)

Last year my colleagues and I set out to fill this gap in our knowledge by testing how fast a songbird could exhibit the Lombard effect when noise levels suddenly changed. As a test species we used wild-type canaries. This species was perfect for our study as canaries sing a lot with little encouragement and produce really long and complex songs. These songs are composed of long strings of repeated bursts of sound known as song elements which can be grouped into different element types.

Canary
One of the canaries used in our experiment

Here you can listen to the song of one of the canaries from our experiment while the image shows a visualisation of song and song elements.

Canary song spectrogram
Spectrogram showing a visualisation of canary song from one bird. Each number indicates a different element type.

To test how quickly canaries could respond to noise we created software which would detect when a canary began to sing, then play a 20 second burst of 75 dB white noise after a random delay of between 5-10 seconds. In this way the first half a canary’s song was sung during quiet conditions while the other half was overlapped by noise which caused the bird to respond by singing louder.

In this recording you can hear how song sounds when overlapped halfway through by white noise.

Canary song spectrogram with noise
An example of canary song overlapped halfway through with white noise. The noise induced the Lombard effect, forcing the canaries to sing louder

Using recordings we were able to work out the strength of the Lombard effect in our canaries by comparing how loud they sang before and after noise began.

We found that in comparison to song elements sung during quiet conditions, song elements sung during the 20 second white noise playbacks were 5.3 dB louder on average. That may not sound like much, but is actually an impressive 84 % increase in song amplitude.

To work out how fast this increase in song amplitude occured we used a statistical technique known as broken-line regression. Using this method we were able to work out exactly how quickly the amplitude of song increased after noise began, and it was extremely fast. Our canaries were able to respond to noise extremely quickly. After just 0.32 seconds of noise exposure their song showed a statistically significant increase in amplitude.

Song amplitude increase canary
Figure showing the speed of the onset of the Lombard effect. Before the onset of noise the mean sound pressure level (amplitude) of the song is shown by the black line with dashed lines showing the +/- 95 % confidence intervals. After noise begins the amplitude of the song rapidly increases and is significantly louder than before the onset of noise after 0.318 seconds. Each point of this figure shows the amplitude of a single song element. The different colours show elements from different recordings.

Our study shows that canaries are able to rapidly increase the amplitude of their song in response to sudden increases in background noise levels. This means that, despite fluctuating and unpredictable changes in noise levels, canaries can ensure that their songs ares till heard. This ability is likely to be particularly useful in urban areas where noise from anthropogenic sources is loud, fluctuating and unpredictable. Given that the Lombard effect is known in all other birds so far tested it is highly likely that other species also possess this ability.


This study is published in the Journal of Experimental Biology and is available here.

If you don’t have access to the journal but would like a copy of the article let me know and I will send you a copy.

My research poster from an animal behaviour conference in Bonn

I have spent the last few days in Bonn, the home of Haribo and former capital city of West Germany, for the annual meeting of the German Animal Behaviour Society (Ethologische Gesellschaft).

I think all who attended the meeting agreed it was a huge success. It was fantastic to spend a few days talking with other behavioural ecologists about their work and also to be able to discuss my own work with other like-minded people. Whenever I attend meetings like this I always come away with a renewed enthusiasm for what I do and with new ideas buzzing around my head for potential future research projects.

This time I did not give a talk myself, but I did present a poster showing the results of my recent work on the Lombard effect in canaries. I will write a full blog post about this soon but for those who might be interested in the poster I thought I would post it here. If you have any questions please don’t hesitate to ask!

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My poster from Etho 2017. A meeting of the Ethologische Gesellschaft in Bonn.

A high-definition PDF version is available here

My PhD viva experience

As I mentioned in my last post I successfully defended my PhD viva (thesis defence) just over three weeks ago. As I was preparing to defend my thesis I found it helpful and often reassuring to read the experiences of other PhD students to get some idea of what I could expect. Of course, every viva will be different but below are some of my thoughts post-viva which I hope my be useful to others.

Preparation

In the weeks leading up to my viva I tried to prepare as best I could by re-reading my thesis and refreshing my memory of the major papers which I had cited often or based my own work upon. Apart from this I didn’t feel like I could really do much to prepare as I had no idea what questions I would be asked. At the time I found this quite stressful because I felt like I should have been working harder and doing more to prepare. Now with the benefit of hindsight I can see that I did the right things.

What my reviewers most wanted to know was that I understood and could explain my own work. Since I had spent the last 3+ years working on it this was not a problem! What I now know is that the preparation for my viva began on the very first day of my PhD. While it was helpful (and definitely recommended) to refresh my memory of the key points of my work in the weeks leading up to my viva,  the real hard work had already been done over the past years.

The warm-up

On the day of my viva I got up early and read a few notes one last time over breakfast. I then headed into my university for a pre-viva chat and coffee with my supervisor. This really helped calm any nerves I had as he seemed quite confident that I would have no problems.

In the hour before my viva began I had to go and register with the secretary before being shown to the room where I would meet my reviewers. Here I had to wait outside for quite a few minutes and it was at this point that I first started to get really nervous. I think because the time waiting gave me the time to think of all the possible worst case scenarios!

Eventually, I was shown into the room where my reviewers introduced themselves and explained what the viva was and what would happen over the next few hours. I was offered drinks which had been prepared for us (tea/coffee/water) before the viva really began. These first few minutes felt like a warm-up before the real questioning began.

Full-speed

The first thing I was asked to do was to explain in broad terms what my thesis was about, why I did it and what I had discovered. This was possibly the easiest question of the whole day as I had spent so long working on my PhD that I could explain it in my sleep. The only difficulty I had was condensing more than three years of results into fifteen minutes of explanation. This meant leaving out everything but the biggest and most important elements of my work.

On a couple of occasions I found myself spending too much time explaining minor details and had to force myself to move on to more important aspects of my work. Nevertheless, this question really helped me to get into the flow of explaining my research and after a few minutes I really felt like I was firing on all cylinders.

After this warm-up question things got a lot more detailed. My reviewers went through each chapter one by one and stopped wherever they had a question about something I had written or wanted some more detail about a particular point I had raised. In almost all cases these questions were not too difficult, and in most cases they were relatively easy to answer.

However, I don’t want to suggest that there were no difficult questions. On a couple of occasions a question was put to me that I couldn’t answer very well or a criticism of my work was made which I could only agree with. During the viva this made me quite uncomfortable, but now, with the benefit of hindsight, I can see that my reviewers pushed me to look at my work from a different perspective and consider new possibilities. This is probably one of the best things to come out of my viva and will really help me as I write-up some of my chapters for publication.

Towards the end

My viva was just under three hours long. It sounds like a really long time but it really didn’t feel like it. After the first few questions it felt more like a friendly discussion that an exam and I relaxed a little bit and started to feel slightly more confident. This, along with the stress and adrenaline really helped the time to fly by.

Once both my reviewers were satisfied that they had no more questions to ask me I was asked to leave the room for a few minutes while they discussed how I did and what the outcome should be. This was probably the most nerve-wracking moment for me as I really had no idea how well I’d done or what outcome to expect. After maybe five minutes I was asked back into the room where my reviewers both seemed happy and congratulated me on passing with minor corrections. This means I  have up to six months to make a few changes to my thesis which in reality should take no more than a week or two.

And relax!

The feeling of relief on being given the news that I had passed was overwhelming and I didn’t really know how to react. The corrections I need to make are only very small and my reviewers really seemed to like my work.

Once the viva was over I had a celebratory pint in the local pub with my supervisor, a reviewer and some friends. At this point I was still dazed, relieved, tired and hadn’t really full absorbed had what just happened. I think it took a full 24 hours before it really sank  in that all of my work over the past years had been worth it. Often it was fun, at times it was hard, stressful and I felt like I couldn’t do it. But now it has paid off and I am happy!


If you are a PhD student about to defend your thesis and have any questions about the process please feel free to email me or leave a comment. And most of all, good luck!

 

The end of the beginning

The very first post on this blog was written while I was still an undergraduate at the University of Derby. Today I am happy to say that I have just successfully defended my PhD thesis on the effects of urbanisation on the behaviour of song birds. This means not only can I order a new bank card with “Dr.” on it, but also that my time as a student has finally come to an end.

thesis-picture
The first draft of my PhD thesis just before I submitted it.

The question I have to ask myself now is what next?

Right now I am working at the Max Planck Institute for Ornithology in Germany and am loving it. I work with a really fantastic research group and I hope I will be able to stay here a while yet to pursue some of my research ideas. After that, I have no idea! I am considering several possibilities including continuing in academia long-term, working for conservation/environmental charities or applying for jobs in government environmental agencies. If you have completed a PhD I would love to hear in the comments what you did next.

As for this blog, I hope to revive it after its long and unplanned hiatus. As all PhD students know, the final year is the most intense and personally challenging. In the last year I have moved to Germany, written my thesis and published a paper. amongst all this I didn’t find the time for my poor blog! Now, however, I have a little more time and I plan to use it to write a series of blog posts on my PhD experience. Both the good and the bad. If there is anything you would like to know about the PhD experience please let me know below!

I also plan to write about whatever I do next. Although it is still quite unclear at the moment I am optimistic for the future and looking forward to the next challenge. The end of being a student me is really just the beginning of the next stage in my life and I can’t wait!

My study species in four facts

ResearchBlogging.org
The last few months have been a blur of conferences, workshops. I attended a fantastic two week course on sensory ecology in Sweden (read about that here and here), I went to London and presented a poster of my work at the annual meeting of the Association for the Study of Animal Behaviour and have recently returned from the Joint meeting of the British Ecological Society and the Société Française d’Écologie in Lille. Time has been flying by and now Christmas is upon us but I wanted to write at least one more post for 2014 so here it is. These are four facts about my wonderful study species the great tit (Parus major).

Great tits have personalities.
My study species.

Every great tit has a unique personality

It’s true, you might think that a bird is just a bird and they are all the same but research has shown that this is not the case. In fact, many species of birds including great tits are now known to have distinct personalities and behave differently to one another, just like humans do. Researchers at Groningen University in the Netherlands found that when they exposed adult great tits to a completely new environment which they had never experienced before some birds were confident and bold and explored their new environments quite happily, while others were much more cautious and did not adapt quickly to the unfamiliar surroundings. Further tests have shown that birds which are bold or shy the first time they are tested tend to stay that way in repeated experiments. These results suggest that personality types are probably fixed characteristics which do not easily change. So, for anyone who’s ever said that animals have personalities, you were right. And it’s not just great tits either; research over the past few years has identified distinct personalities in a huge number of species including mammals, birds, insects and even anemones!

Different personalities. Great tits are not all the same. Image credit: Per Tillman.
Different personalities. Great tits are not all the same. Image credit: Per Tillmann.

City great tits just aren’t as colourful as their countryside cousins

With their bright yellow breast feathers and marked and glossy black plumage great tits are hard to miss at the best of times and are particularly conspicuous during the breeding season when the males are singing their hearts out trying to attract mates. The purpose of the great tits striking colouration is not fully understood but it is likely that females are most attracted to those males which have the brightest and boldest feathers. It is unfortunate then for city birds that their feathers just aren’t as bright as their rural counterparts. A likely explanation for this is that the same carotenoid compound which is used to create the bright yellow colour in great tits feathers is also an anti-oxidant which reduces the physiological stress caused by oxidising pollutants in the environment. As urban birds are known to be exposed to much higher levels of pollutants than rural birds it may be that urban birds are forced to divert carotenoids away from their feathers and use them instead to reduce the levels of stress and cell damage that oxidising compounds can cause. Evidence of this comes from a study at Göteborg University in Sweden which found that the increased oxidative stress faced by urban birds correlated well with reduced levels of carotenoid pigments in their feathers.

Great tits can be incredibly aggressive

They might look cute and friendly but in reality great tits can be incredibly violent, and particularly so during the spring and summer when males are competing for the best breeding territories. During this period male great tits mark their territories by singing at regular intervals and this signal tells other males to move on and find an empty territory of their own. This works most of the time but not always. Sometimes males deliberately invade territories and may attempt to mate with the resident female or even try to force the current territory holder out and take over completely. If this happens the first thing the resident male will do is to sing frequently and loudly in an attempt to show their strength and to drive the intruder away. Should this not work things typically escalate quickly as the resident male flies back and forth across the intruder before coming into full-on physical confrontation. It is not common to see fights in the wild as invaders will usually leave before it comes to actual violence. It does happen sometimes though and you can see the result in these incredible videos.

Great tits sing at higher frequencies in cities than in rural areas

Cities are notoriously noisy places full of cars, people and factories, with aircraft flying overhead and noise from building sites, road repair crews or similar urban development projects. This level of noise is something which wild animals have only had to face in the last century or so, and for species which communicate using sound it could make life in cities very difficult as their vocal signals are easily lost amongst the clatter and din of urban life. Great tits are a good example of a species which might be expected to fare badly in urban habitats as the males rely on communicating by song to defend their territories, show aggression towards rivals and attract mates. To make matters worse, the typical song of a great tit lies in exactly the same frequency range as the background noise of most cities and this means that when a great tit sings its song is quickly swamped by urban noise and cannot be heard by other birds. Yet despite this, great tits are one of the most common song birds seen in city parks and at garden bird feeders so how do they manage to cope with the noise problem? The answer is simple but ingenious. Urban great tits have adjusted their typical song frequency so that they now sing around 350Hz higher. That might not sound like much but experiments have shown that this small adjustments means that the song of urban birds travels above the low-frequency rumble of urban noise and can still be heard by other birds, even at long distances. Genius!

When there are high background noise levels great tits adapt by singing at a higher pitch. Figure from Slabbekoorn and Peet (2003).
When there are high background noise levels great tits adapt by singing at a higher pitch. Figure from Slabbekoorn and Peet (2003).

References

Every great tit has a unique personality

Dingemanse, N. (2002). Repeatability and heritability of exploratory behaviour in great tits from the wild Animal Behaviour, 64 (6), 929-938 DOI: 10.1006/anbe.2002.2006

City great tits just aren’t as colourful as their countryside cousins

Isaksson, C., Örnborg, J., Stephensen, E., & Andersson, S. (2005). Plasma Glutathione and Carotenoid Coloration as Potential Biomarkers of Environmental Stress in Great Tits EcoHealth, 2 (2), 138-146 DOI: 10.1007/s10393-005-3869-5

Great tits sing at higher frequencies in cities than in rural areas

Slabbekoorn, H., & Peet, M. (2003). Ecology: Birds sing at a higher pitch in urban noise Nature, 424 (6946), 267-267 DOI: 10.1038/424267a

My poster for Behaviour 2013

I’m going to be spending the next few days in Newcastle at Behaviour 2013, a conference billed as the largest gathering of researchers working in the field of animal behaviour this year. Today we had talks on assassin bugs that actually attack and eat spiders on their webs, to bats that home in on the call of their unfortunate prey, the túngara frog. Tomorrow it all starts again bright and early with talks on everything from avian cognition to social learning and parental care. It’s so rare to be in a place where everyone shares my enthusiasm for animal behaviour, it’s great!

I’m not just going to listen to talks though, oh no,  I’m also presenting a poster showing some of what I’ve been working on for the last year. For those of you that won’t be there I thought I’d put the poster up here, I’ve received some good feedback on this so far but if you have any comments I’d love to hear them.

Click here for a high-res pdf version.

ASAB Behaviour 2013 poster