Just one of the areas where photo-ID helps in our research:
Researchers on North Rona (our other main study site) have been looking at seal personalities over the last couple of years to see how differences in maternal behaviour may affect reproductive success. This study used photo-ID to identify females on a daily basis and from one year to the next to look at consistences in behaviour over time. Here are a few links to the findings that have recently been published:
With the promise of more gales, we decided to escape whilst the going was good and left the island on Monday. We had planned a leisurely finish, but there was a risk of being stuck for several more days if we didn’t leave a day or two earlier than planned. Our work was pretty much finished and it was only really clearing up and packing that needed to be done so we decided to go for it. Six people cleaning and packing can get the job done in an evening, though Jo was still hoovering at midnight!
We weren’t the only ones leaving the island early – it seems like this was an early season for many of the seals. Although there were still a few pups born in the last week, most of the females had already gone and even the weaned pups were leaving. With the island quieter than I’ve seen it before at the end of the season, we were able to explore the north end of the island during our last days there without worrying about disturbing any of the breeding seals. We came across weaned pups in many of the pools, busy checking out a new use for their flippers and discovering what swimming was all about. We even came across this little one checking out the sea itself – it took a while to battle through the breaking waves, but we eventually saw it beyond the break. Perhaps this was its first foraging trip….
weaned seal pup battling the waves
hmmm... maybe I'm not quite ready to go to sea yet....
this isn't too bad...
hmmmm.... getting a bit choppy now...
taking a breather....
these waves are definitely getting bigger...
Phew, made it! Now where are these 'fish' creatures??
mum and pup, with pup at one day old
Same mum and pup, with pup at 18 days old
The average length of lactation for a grey seal is 18 days and we’ve seen some phenonenal mass changes in that time. Pups can put on 1.5 to 2kg a day whilst their mums can easily lose 3kg per day. Amanda has been documenting some of the mums and pups she has been watching with daily photographs – the two photos above show one mum and pup at the start and end of lactation. The pup’s huge weight gain is due to the fat-rich milk that the mum produces – if you imagine eating smoothies made of double cream and butter you’ll have an idea of what the milk is like for the pups. The mums don’t eat anything during lactation (many of the females on the Isle of May don’t even go to sea during lactation) so their reserves for milk production and general maintenance of their own body are completely dependant on the blubber stores that they arrive with. We always have a few females that go that extra mile and stay with their pup a few more days and it really is incredible to see the difference in them at the start and end of lactation.
We had a nice suprise for Kelly today when we spotted a tagged yearling sheltering from the wind, as it turned out to be one of the ones she was studying last year. The survival rate for grey seals in the first year is only about 50% so she was very happy to see him back on the island. Last time she saw him, he weighed 52kg – this time he was only 3kg heavier, but he has lost his pup fat and is now a lean bundle of muscle and an impressive 128cm long. Not bad for a yearling!
- ‘K’ as a yearling in 2011
'K' as a weaner in 2010
Now that he has survived the first year, he has a good chance of making it to adulthood, so maybe we’ll see him in again in the future.
The photo-ID work at the Isle of May and North Rona is currently restricted to females for a number of reasons. Historically, SMRUs larger photo-ID projects have been based on photographs of heads in the water and the computer-aided matching program uses the sleaker head shape of the females for its modelling. Sub-adult males can be difficult to distinguish from females as they have a similar head shape, but as they mature, males develop a broader, more Roman, nose. The change in head shape as the males mature makes it much more difficult to use a computer to look for matches between pelage patterns – they also get a lot of scarring on their necks from fighting and this often makes it very difficult to see any markings. Although we now use other areas of the body as well as the head, the pelage of males also tends to darken as they mature. This changes the contrast between areas of pelage so that only the most striking marks remain visible on the males. The picture below shows two males – the one on the right could be one of many males we see, with little in the way of distinguishing marks. Males have a tendency to move around the colony depending on the availability of females and the individual male’s ability to deter other males from the ladies of his choosing, which means we would be hard pressed to distinguish the male on the right from any other, similiar-looking, male. The one on the left could be identified from day to day, but as these well-marked males are in the minority, we tend to ignore them most of the time as far as photo-ID goes, and just concentrate on the females.
One male did catch our interest the other day though – we spotted this tagged guy coming out of a pool.
We tag an equal number of male and female pups every year to look at survival over time so we were definitely interested in trying to find out who he was. If we are lucky, we can get a photograph of a tag number (or read it with binoculars or a telescope) when the seal spreads its flippers.
This takes a lot of patience, but it is worth it for females because we can then use their pelage pattern instead of the tag number, which allows us to follow their survival much more easily. In this instance, we managed to read the male’s tag eventually and found out that we had seen him last year (we had taken several photos of him because he was tagged although we hadn’t got the tag number that time). Even though we don’t routinely use photo-ID on the males, it definitely came in handy this time, and we’ll be able to identify him next time we see him, as well as now knowing much more about him.
We’ve been lucky this season in having more than our fair share of good weather, and now that everything is slowing down with the long-term study females I’ve had the odd half hour or so to get a few photos that aren’t just work-related.
We have one particular female that likes to make use of an old brick tank every year – it fills up with rainwater and she treats it like her own private bathtub! I happened to be in the right place today to get a sequence of pictures showing her atheletic ability at getting into it. Most people probably wouldn’t imagine that seals are good climbers, but they are pretty strong – if they can get their front flippers up there, they can get over it.
Even though the colony is much quieter now, there are still plenty of weaned pups about and we’ll be busy with vocalisation recordings and weaned pup behaviour for a couple more weeks.
It’s got to that point in the breeding season where there are more weaned pups around than adults and we regularly come across little gangs of fat furry seal pups! Kelly is back from North Rona and came out to the Isle of May at the end of last week to continue her behavioural studies on these little characters. Click here for a short video of some investigative play showing a weaner using its vibrissae and teeth to check out a piece of wood.
Groups of weaned pups are starting to become commonplace around the island
Today’s blog entry comes from Amanda who is studying pup vocalisations. Amanda spends a lot of her time hiding behind the walls in the southern part of the island so she can get close to pups without disturbing them. She records the noises the pups make and videotapes any associated behaviour, and gives a brief explanation of her work below.
Example video of pup vocalizations
Grey seal pups produce vocalizations such as growls and moans (click on link above), which have been found to be individually distinctive. Despite producing unique calls, these vocalizations do not appear to play a role in mother-pup recognition. Past research has shown that juvenile grey seals are capable of vocal learning, which has inspired research into their vocalization use and learning. Currently some of the pups on the island are being recorded to investigate their vocal development from birth, which will give insight into the effects physiology and environment have on repertoire development.
The spectrogram below is a visual representation of a single call from the young pup shown in the video above.
Spectrogram of pup call
The horizontal axis gives the time of the call (in this case 4 seconds) and the vertical axis gives the frequency in kHz. The color of the spectrogram indicates the volume of the call, with the red parts being the loudest, and the horizontal bands show the harmonics of the call.
Not all seals are photogenic – some of them have definitely had a bit of a tough life. This female, for example, appears to be pretty much blind. Her behaviour towards other seals suggests that she can detect movement but not much more than that, and whenever another animal approaches, she stretches her neck as far as she can with her vibrissae (whiskers) extended. Seals are well adapted to their aquatic environment and able to hunt in dark and muddy waters by using their vibrissae to detect food – the vibrissae are very sensitive and provide seals with tactile information about their environment. It’s quite amazing how animals like this manage to survive in the wild and find their way back to the breeding colony each year. This female has raised a healthy male pup weighing 47kg so obviously hasn’t had many problems finding enough food to get her through the breeding season.