Snares census

Snares penguin foraging ecology and breeding behaviour
In the southern spring of 2002, Thomas Mattern, Melanie Masarro and I travelled to the Snares Islands in order to undertake research on the Snares crested penguin. We were seeking answers to a variety of questions including where and on what do the penguins feed and why do they raise just one chick.

Where do they forage?
We hoped to determine where the males and females fed during the incubation period when they in turn take trips of around 10 days duration and where the females feed during the chick guard stage. In order to do this we used small Global Positioning System (GPS) devices packaged with a datalogger and attached these to the penguins backs using the "Tesa tape" technique. Unfortunately, these devices had never been used on penguins but we knew that they had some shortfalls, including a limited battery life.

After closely monitoring the start of the male exodous, we fitted six devices to birds who we hoped would soon leave the colony and then monitored their departure. The following 10 days we anxiousy awaited their return. FInally, the first of the logger birds arrived home and we carefully removed the device and downloaded the data. Alas, aside from a few positions acquired in the colony before the birds left, the memory was empty. Gradually the other 5 logger birds arrived home, but none had any data. Needless to say we were deeply disappointed.

We spent several days fitting new batteries to the devices and trying to understand why no data was recorded. One possibility was that the salt-water switch, instead of helping save battery power may have actually prevented a fix being obtained at sea. After disabling the switch by expoying over it, we fitted a logger to a female bird that was making day trips. Again we anxiously waited for the bird and some data to return, but once again we were thwarted - the bird dutifully arrived home but no data had been recorded.

Recording dive depths
After abandoning the GPS loggers we still had one last hope to gain some foraging trip data - dive loggers. These are small devices fitted to the penguins back in the same way as the GPS logger, except instead of position they record dive depth, duration light levels and temperature. We were lucky to have 3 such devices, 2 Wildlife Computers MK7s and 1 Lotek model. Unfortunately, one of the MK7s and the Lotek both suffered failures before they could be deployed. The remaining MK7 was fitted to an incubating male and it spent two days at the colony before heading off to sea. 14 days later it finally arrived back at the nest. I nervously removed the device and rushed back to the hut to download the data. Once again our hope were dashed as it seems the battery failed before the bird got to sea.


One thing we were able to do was look at what the birds were eating, or at least what they were bringing home. We got stomach content samples from both male and females by stomach flushing them. This technique, otherwise known as the water offloading technique, involves inserting a tube down down the throat into the stomach and filling it with water. Once it is full, the tube is removed, the penguin inverted and squeezed, the stomach contents ending up in a handily placed bucket.
While the penguin isn't exactly happy about being subjected to this process, aside from having an empty stomach it is otherwise unharmed.

It was known from spillage from around nest sites that Euphausids (small shrimp-like animals) make up a large proportion of the diet. We found that this was indeed the case with some 60% of stomach contents being one species of euphausid. Squid and octopus made up another 20% and the remaining 20% was fish. This last item was most interesting, as the species most commonly seen was an as yet unidentified species of pipefish, something we didn't expect to see.

Domestic violence
We were all astonished at the violent encounters between neighbouring penguins and in particular the capacity of the females to withstand prolonged attacks from male neighbours. The purpose of these attacks is not clear, although in many cases nest material is robbed from the nest. In one case a female was forced to abandon her eggs and these were temporarilly taken over by the intruder. Just what advantages there can be to these stagegies is a mystery.

Chick feeding
Because one chick usually dies within a few days of hatching, we observed the chick feeding patterns to see if one chick begged more than the other and thus received more food. While the results have not yet been analysed, we saw a great variety of begging and feeding behaviour. Some chicks appeared to beg little and thus got nothing, while other siblings begged equally and both got food. We were able to see the demise of some of the weaker chicks who fell from the nest and soon succumbed to the cold or from attacks from neigbouring nests.

What next?
Many questions relating to crested penguin behaviour still remain unanswered, as does the foraging behaviour. We hope to be able to return to the Snares islands in the future with better equipment in order to answer some of the riddles.

But wait, there's more ...

In 2003 Thomas and I went back to the Snares. Click here to read more >>>

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