Foraging behaviour of gulls

Monika Reiss, PhD student at Liverpool John Moores University, who we interviewed recently, has produced the following blog for us about the foraging behaviour of gulls in general, and Liverpool's gulls in particular.

Juvenile herring gulls on the Mersey, April 2020. Photo credit: Debra Williams

 

Diet

Gulls are omnivorous and mostly opportunistic seabirds. Their natural foraging material found in the water can be any kind of marine fish, invertebrates, shrimps, cockles, crabs, crayfish, clams and mussels. Naturally found food in the terrestrial environment may include worms, insects and other birds, their offspring and eggs. It is known that herring gulls are cannibals and they often prey on the adults of their own species and their young. The biggest of all gulls – the great black-backed gull – can even eat common terns, Manx shearwaters and other big gulls. The common and black-headed gulls additionally eat seeds and grains. Their non-natural or anthropogenic food includes fast food like chips, fried chicken, burgers, human refuse gathered from rubbish bins or refuse tips, and discarded fish from fish-processing plants. Their nutritional intake and needs may vary between the seasons; for example, during the breeding period (April-August), the female needs food rich in calcium and protein as she is laying eggs. After the eggs hatch, the parents need to provide a sufficient amount of calories, not only for themselves, but also for their chicks. Gulls’ nutritional needs decrease during the winter when their chicks have fledged.

How do they get food?

Gulls can obtain food in the air, water and on the ground; thanks to many different techniques for sourcing their prey, they can meet their foraging needs. Most of those birds forage on the tidal flats during the low tide; exposed marine fauna is vulnerable and very easy to catch. Gulls can catch their prey by simply walking on the mud flats and picking up small fish or invertebrates. If they find something more difficult to get into, like, for example, shellfish, they pick it up in their beaks and drop it from height onto the rocks, until the shell cracks. Something similar may happen with small mammals or other birds’ chicks: they can either drop them or drown them in the water. Gulls very often fly near shores where they can effectively spot any available food and pick it up. When they find food, they often perform a long, loud call to let other birds know about this potential food source. This behaviour works along with the ‘tit for tat’ rule, and most likely, in the future, this favour will be returned. While swimming – or, rather, ‘loafing’ on the water – birds can passively search for food as well. When they notice a movement under the surface, they can shallowly dive to catch the prey. The common gull has an amazing ability to hover above the surface of the water, with its head down, and can catch fish without diving! Gulls also like to gather around freshly ploughed fields where they can forage on worms and insects. Big groups of gulls are often seen flying behind fishing boats, where they can often steal fish from the fishing nets. Another act of theft performed by urban gulls is stealing human discards from refuse dumps and small rubbish bins; bolder gulls even try to snatch food from people’s hands. But theft is not related to only anthropogenic sources of food – gulls can steal a meal off other birds, too, and sometimes this can cause an air fight.

Where do they get food from?

Gulls are seabirds so their natural food is usually found in waterways like the River Mersey or the Irish Sea, but sometimes they also use small ponds or lakes, for example, lakes in Sefton Park or Princes Park. They also enjoy the beaches at Formby and Crosby. Gulls prefer open spaces which are not full of trees, and they actively avoid dense forests; it is easier for them to spot a predator in an open space. Therefore, they also forage around Stanley Park in Anfield or Wavertree Playground. Urban gulls of Liverpool, especially during the summer months, take advantage of tourists willing to feed them along the docks and also in the city centre. Gulls very often sit on the rooftops, outside restaurants or fish and chip shops, and watch for any refuse or wait to steal the food out of customers’ hands. Another source of human discards is the ‘rubbish tip’ or recycling centre, for example, Otterspool and Old Swan Waste Recycling Centres. Birds can easily access food discards and can very often spend i several hours in these places. As mentioned before, gulls prey on different gulls’ chicks and eggs; this can happen during the breeding season on the rooftops of buildings (shopping centres, university buildings, houses) if they are urban gulls, or in natural colonies like the one in the salt marshes in Southport.

Given that we are now reducing the amount of food waste that is sent to landfill, and that there have been many fewer people and thus food refuse around our city centres recently due to the Covid-19 lockdown, it will be interesting to continue to monitor our urban gulls, to see how they react to this reduction in anthropogenic food sources.

Edited by Debra Williams

Q&A with Monika Reiss, PhD student studying feeding behaviour in Liverpool gulls

Herring gull (Larus argentatus) with litter

Photo credit: Partonez/CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

I ‘met’ Monika as I was volunteering behind the scenes for World Seabird Twitter Conference 6 in May this year, and she submitted an abstract and then gave a presentation during the conference. Monika’s work relates to the feeding behaviours of herring gulls (Larus argentatus) and lesser black-backed gulls (Larus fuscus) in Liverpool, which is certain to be of interest to RSPB Liverpool members. Hence, we had a virtual chat so she could explain more about her work, her background and what brought her to Liverpool.

Debra Williams: Hi Monika. Your Twitter presentation for #WSTC6 was really interesting, and we’ll talk about it later, but first I would love to know what first attracted you to gulls. Did this fascination with them start when you were young?

Monika Reiss: Hi Debra, thank you for inviting me to take part in this Q&A. I’ve been fascinated with animals since I remember, especially with birds and companion animals. Having said that, I saw a gull for the first time in Liverpool! I got particularly interested in gulls when I did my internship at Liverpool John Moores University. I was helping one of the researchers in gathering data about the aggressive behaviour of urban gulls. Since then, I’ve been astonished by their intelligence, behaviour and ecology, but I still think there’s much more to find out about these species, especially given that some of the gull species are endangered in the UK.

DW: And why did you decide to focus on urban gulls and their feeding behaviour in particular?

MR: I believe that not only gulls are affected by urbanisation, all animal species need to adjust very quickly to the new environment. Gulls are one of those species which are thriving in urban areas and rapidly adjust to the changes. Originally, my project was supposed to be limited to the feeding behaviours in Liverpool; however, this has changed and now I’ll also investigate their movement patterns, breeding behaviour and influence of urbanisation on the choice of nesting sites. I decided to focus on this species because I think there’s still a lot to discover in their behaviours and how they differ from their rural conspecifics [members of the same species]. I also want to raise awareness about their ecology as most people see them only as a pest, which I don’t think should be the case. It’s the role of scientists to educate people about the value of these seabirds.

DW: You are originally from Poland, but are registered for your PhD in Liverpool. What brought you here?

MR: I came to the UK to study zoology at the University of Nottingham first. Later on, I realised that animal behaviour would be a better fit for me, and that’s what I’m really interested in. I chose Liverpool because of its atmosphere and the course in animal behaviour at the university. And then I found gulls, which changed my life forever. I’ve also met a lot of amazing people in here, including my husband, and I decided that I would like to stay here for longer.

DW: And how have you found being locked-down in the city as a result of Covid-19? Are you still able to carry out your research?

MR: Being in the lockdown is not the perfect situation, but it gave me a lot of time to read and to work on my research project; I’m trying to use this free time to the fullest. While being in the lockdown, I also had the chance to participate in the earlier-mentioned Twitter conference, which was a valuable experience.

I’ve been working on my research proposal since last September, so I’m still in the very early stages. Unfortunately, right after I officially started the doctoral programme, in February this year, I had to change most of my plans. Some will have to wait until next summer, but I’m still working on this. Since the lockdown started, I’ve been planning the new methodology because I have only three years to finish the PhD, so I need to act quickly. At the same time, I’m still conducting monthly transect counts in Liverpool and North Merseyside and I’m also doing weekly counts of gulls in the city centre and parks in South Liverpool, and collecting data on their activity. I’ll be involved in more fieldwork next year, when hopefully everything is back to normal.

DW: And do you think that fewer people and therefore discarded food around the city centre has had an effect on the gulls in terms of their feeding behaviour and where they congregate?

MR: Yes! I definitely think that the ‘coronavirus effect’ has had an impact on gulls’ feeding behaviour. I’m going to compare my observations from this year with next year’s data and we could figure out how they dealt with the situation. There have been a few reports about gulls' increasingly aggressive behaviour all over the country and Europe! My friend from Rome said that it’s the first time she has seen gulls getting so aggressive towards other birds. I have personally found that there’s not that many gulls visible around Liverpool. I think breeding season played a part in it, and it overlapped with coronavirus lockdown.  Gulls need more food to feed their chicks during this time, which could make them frustrated that there's no human refuse around. This could make them travel long distances to the seaside to obtain natural food. Possibly this could also have an impact on why we don't see many of them in Liverpool city centre.

DW: I live by the river and sometimes hear the gulls squawking in the middle of the night – presumably they are feeding at low tide, even though we’d expect them to be asleep! Is this something you’ve noticed when conducting your research?

MR: Actually, before the coronavirus I was supposed to investigate the nightlife of gulls. I thought that they would be more active during the weekends when Liverpool is full of people with takeaway meals. Unfortunately, because of lockdown, I wasn’t able to develop this idea further. There’s not much research done on what exactly gulls are doing during the night, so it’s still undiscovered territory. So far, we only know that laughing gulls (Leucophaeus atricilla) definitely forage at night; scientists are not sure about the rest of the gull species. As you said, gulls most likely forage on tidal flats during the low tide; that's why you can hear them making noise at night. I think it’s worth investigating what our urban gulls are up to when we sleep.

DW: I think so too! Moving on to your Twitter presentation: it explained the results of your work on herring gull behaviour to date in the ‘four tweets only’ format used by the conference. The gifs you used gave an insight into the gulls’ behaviour. How did you find out that information and is it a very time-consuming process?

MR: It was quite challenging to put all information into just four tweets, but it was definitely a fun experience. In my gifs, I included unpublished results from my undergraduate dissertation. It took me six months to do the weekly counts during the different tidal elevations to come up with the idea that gull abundance is related to different factors including tides, temperature and number of humans around. It wasn’t really difficult to do as it was a purely observational study, but it was very time-consuming. But this surely paid off, as I based one of my methods for the PhD on what I discovered during my BSc.

DW: And how did you find participating in a Twitter conference?

MR: It was a very unique and interesting experience! It was also my first conference ever so I’ll remember it for a long time. I found the whole process incredibly easy to follow and people who worked behind the scenes – including you – were very knowledgeable and extremely helpful. I’ve met a lot of nice people and kept in touch since! I have also learnt new things about other bird species which I knew nothing about before. I believe that this kind of conference should be organised not only in the era of coronavirus, but other organisations should also follow the example of WSTC: it’s carbon-free and reaches a much bigger audience. I will also happily take part in next year’s World Seabird Twitter Conference 7.

DW: Thank you. I found being involved in WSTC last year and this year very interesting too. Finally, what are your plans for the future, after you’ve finished your PhD? More gull research or something else?

MR: I think it’s too early to say, but I would love to do more for the understanding of birds’ behaviour. I’d like to discover new behaviours, develop conservation techniques, but also educate people about the importance of birds for the ecosystem. In the future, I also want to get more involved in activities and events organised by the Liverpool RSPB group. Thank you for inviting me to this Q&A, it was a pleasure!

DW: Thank you, Monika. Keep an eye on the Liverpool RSPB group’s Events page – there are some interesting walks and talks lined up for later in the year and it would be great for you to come along. We’d also love to hear more about your research, so please keep in touch.

RSPB Liverpool on Nature Watch, BBC Radio Merseyside, 23rd May 2020

Although things are quiet on the RSPB Liverpool events front due to the coronavirus, Chris has still been contributing to BBC Radio Merseyside in his role of nature watcher. Most recently, as well as answering listeners’ questions, he discussed a number of nature-related topics with Helen Jones, including:

·         Screaming swifts and how to help map them (https://www.swiftmapper.org.uk/). 

Common swift – photo from Wikimedia: AlexeySokolov1971/CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

·         The RSPB’s Big Wild Sleepout Lockdown Edition, which took place on Saturday, 23^rd May.

·       #NoMowMay, which some councils have participated in this year, leaving grassy areas uncut so that wildflowers can emerge, supporting pollinating insects such as bees and hoverflies. Bees are one of our most important pollinators, and we rely on their hard work for much of what we eat. They pollinate the flowers that produce some of our vegetables, fruits, nuts and seeds, and help to spread colour through our landscape. Bees are vital in keeping up the health of our ecosystems, so we need to give them the biggest chance possible to thrive.

Protected verge, Northants – photo from Wikimedia: Michael Trolove, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=13472961

·         What to do if you find a baby bird on the ground:

If it looks healthy and well, like the young linnet in the photo below, leave it alone.

Fledgling linnet on the ground at Garston Coastal Reserve – photo by @birderjack

If it’s being fed by a parent bird, like the young stonechat in the photo below, leave it alone.

Fledgling stonechat being fed by parent bird, Garston Coastal Reserve – photo by @birderjack

If it’s in the nest being fed or looking healthy and well, like the baby song thrushes in the photo below, leave it alone.

Song thrush feeding young in the nest – photo from RSPB Images

However, if it is definitely injured, seek advice from the RSPCA or a local wildlife charity.

·         Looking ahead, we should shortly be seeing some of our beautiful native orchids in flower – species such as the pyramidal orchid and the bee orchid.

Pyramidal orchid, Formby – photo by Chris Tynan

Bee orchid – photo from Wikimedia: Henry Hemming/CC BY (https://creativecommons.org/licenses/by/2.0)

All of the above can be found in our local area, without having to make a long trip to see them, and one of the few good things to come out of the coronavirus situation has been the increase in sightings – and thus knowledge about – of what we think of as ‘uncommon’ species around Merseyside. For example, eider ducks have been spotted flying along the Mersey and then roosting on a sandbank, then bobbing on the river; a cuckoo was seen flying along the river – no doubt using it as a navigational aid; local fields have provided a brief stopover for other birds on their way to their breeding grounds, etc. Without the eyes and ears of keen local naturalists who are currently unable to wander further afield, the presence of some of these species might have passed unnoticed.

If you would like to record your sightings, Merseyside BioBank has a link to an excellent resource, iRecord (https://www.brc.ac.uk/irecord/). Submitted, verified records are available to national recording schemes and societies, Local Environmental Records Centres, and other individual records and organisations, thus building up a crucial map of areas of importance for the wildlife that calls this island home, or which visits for a brief period.