By Rachael Orben, Assistant Professor, Seabird Oceanography Lab
Fieldwork often comes with the unexpected. It is the reason why field work is so exciting – not only discovering something new about a species and ecosystem, but it is also often the catalyst for the development of novel ideas and projects. However, designing a successful field campaign to a new location (and acquiring funding) requires preconceived expectations that are not too far off from reality. Working with colonial breeding seabirds and pinnipeds has its advantages since these animals are predictably found at their colonies during the breeding period. However, breeding failures can be worse than expected (see my blog on red-legged kittiwakes) and as I just learned, sometimes almost everything can be surprising.
At the end of August, I returned from a 6-week winter field campaign on Bird Island in the Falkland Islands led by Dr. Alastair Baylis a Senior Research Fellow at the South Atlantic Environmental Research Institute. We were there to study the fine-scale foraging ecology of South American fur seals. Despite a healthy research community in the Falklands, very little is known about South American fur seals in the region. Our time on Bird Island was probably the first time people had been on the island in winter since the days of sealing.
So, what did I find surprising?
I will list them here from slightly mundane to the very surprising.
1) First of all, it was winter and I expected it to be cold.
This is probably a case of me not doing my pre-field season research, but it was pleasantly not as cold as I expected. Generally, the temperatures were above freezing, which made doing everything much easier. Of course, I still wore lots of layers and drank lots of hot drinks, but overall it was fairly mild. It was also less windy and less rainy than I had imagined and we had some beautiful sunny days.
2) I had hay fever!
Not something usually anticipated for winter field work, but the tussac grass was flowering and that left me with itchy eyes, a stuffy nose and lots of sneezes. I should mention that tussac grass is everywhere and many of the tussacs are taller than a person!
Now for the science surprises.
3) FEMALE Fur Seals took foraging trips That were much longer than we had anticipated.
We had a couple of females leave the colony and go on foraging trips for 10 days, others for ~2 weeks, and others for over 3 weeks! Previous work on the island indicated that female fur seals might take 4.1 +/- 2 day trips (Thompson et al. 2003). Fortunately, we were on the island for the long-haul (6-weeks shower free) so we were able to wait them out and retrieve the tags (and the data) when the females came home. The differences in trip duration could simply reflect annual changes in prey availability, but we know very little about what fur seals are eating, especially during the winter (Baylis et al. 2013).
4) albatrosses were attending their colony.
As a reminder, this was the middle of winter. Generally, black-browed albatrosses do not return to their colonies until September since they lay eggs in October (Strange, 1992). There weren’t many birds the day we arrived in mid-July (n=9), but even so, that was odd enough that I began taking photos of the colony each day with the plan to count birds and quantify colony attendance.
…and for the most surprising of all…
5) South American Sea Lions males were killing and eating female South American fur seals!
We were slow to realize what was happening since it was so unexpected. After we deployed our tracking tags on fur seals we spent many hours at the colony simply observing. We started to see things that didn’t quite make sense. Females cautiously approaching the water. Male sea lions hanging out in the water. Then Dr. Baylis saw a male sea lion go up into the colony and grab a pup and eat it! Shortly after that, we saw two male sea lions chase a female out of the water and up the hill towards the colony. One male eventually came back down to a tide pool with a female he had killed in his mouth. From that point, it because very clear what was happening and we saw multiple kills.
It is unknown how often male southern sea lions eat fur seals, but it has been observed in the Falklands before, both in the 1970s and in more recent years (Gentry & Johnson 1981). Worldwide, sea lions are known to occasionally eat fur seal pups (Gentry & Johnson 1981, Harcourt 1993, Bradshaw et al. 1998), but people have rarely observed sea lions predating females.
Our three scientific surprises are really what field work is all about. We came home with the tracking data we were hoping for and we came home with something arguably more valuable. We can use these new observations to make informed hypotheses about how marine predators fit into the ecosystem in ways that before our visit to Bird Island we would have never have expected. Hopefully, we will have a chance to go back!
References
Baylis AMM, Arnould JPY, Staniland IJ (2013) Diet of South American fur seals at the Falkland Islands. Marine Mammal Sci 30:1210–1219
Bradshaw CJA, Lalas C, Mcconkey S (1998) New Zealand sea lion predation on New Zealand fur seals. New Zealand Journal of Marine and Freshwater Research 32:101–104
Gentry RL, Johnson JH (1981) Predation by sea lions on northern fur seal neonates. Mammalia 45
Harcourt R (1993) Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru. Canadian Journal of Zoology 71:1908–1911
Strange, IJ (1992) Field Guide to the Wildlife of the Falkland Islands and South Georgia (Collins Pocket Guide)
Thompson DR, Moss S, Lovell P (2003) Foraging behaviour of South American fur seals Arctocephalus australis: extracting fine scale foraging behaviour from satellite tracks. Mar Ecol Prog Ser 260:285–296
