Penguin Island, 50 kilometres south of Perth and just 600 metres offshore from a rapidly growing urban area, is home for a very special colony of Little Penguins, which are the smallest of the penguins with an average height of 33 centimetres. Penguin island is not only the largest colony in Western Australia, but it also has the highest conservation status of all major colonies in Australia. In addition, there are no Little Penguin colonies further west in the world.
In the Perth region, a smaller colony is also found on Garden Island, just seven kilometres north. It lies at the western edge of Cockburn Sound, the busiest bay in Western Australia. The two colonies together are regarded as one “metapopulation”.
This metapopulation of Little Penguins is the most northern in WA. It is facing an increasing range of natural, anthropogenic and climate-change threats.
From August-December 2011, the number of penguins found dead increased four-fold. Forty-nine penguin corpses were found on the foreshore between Safety Bay and the mouth of the Donnelly River, some 400 kilometres around the coast from Penguin Island, as well as on Penguin Island. The penguins were mostly banded or microchipped, so I know that most of them came from Penguin Island.
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This “marine heat wave”, as it has been labelled by the Department of Fisheries, is suspected of causing a decline in stocks of fish that the Little Penguins rely on for food. Indeed, sandy sprat, usually their major prey item while raising chicks, were not found in the penguins’ diet in 2011. The species of fish the penguins were feeding on was determined by analysing the DNA in their faeces.
The penguins also had the worst breeding season since monitoring of this colony began in 1986, with many fewer penguins even attempting to breed. The penguins must remain close to the colony while raising chicks, so they can return each night or two to feed them, so it is likely that the nearby fish resources were much less abundant than normal.
If this wasn’t bad enough, the lack of fish has most likely contributed to more penguins being found dead during their annual two-week moult. Penguins cannot go to sea and catch fish while they are moulting, so they must build up enough fat and protein before moulting to “feed” this very energetically demanding process of making new feathers. If the fish are less abundant, and the penguins have to travel further to catch them, then they can’t build up enough reserves to last the fasting stage of moult.
A boat ramp has recently been constructed seven kilometres south of the colony. We don’t yet know if a potential increase in watercraft used in the area has caused this increase in deaths from injuries. The penguins could be weaker due to starvation and unable to get out of the way of the watercraft, or it could be a combination of both. We need to know more about the seasonality of dead penguins, where they are found and their causes of death, to know what effect the boat ramp is having.
Perth has just experienced its hottest summer on record. This also contributed to a number of deaths, particularly in moulting penguins. They are unable to leave the island until their new feathers have become waterproof, so some penguins died from overheating.
It was probably lucky that there were very few chicks that hatched this year. Otherwise they could have died from overheating too, as I have witnessed in past years. The predictions for the changes associated with climate change – warming temperatures and less rain in the south-west of Australia – do not bode well for this colony of penguins.
It’s hard to know how the mortality and low breeding observed in 2011 will affect the overall survival of the colony. Certainly, a population estimate I undertook in 2011 showed that there were fewer adults on the island compared to the estimate of 2369 penguins in 2007. However, this is likely to be an indication that there were fewer penguins breeding, as was certainly identified from the monitoring of nest sites.
Seabirds are long lived, the adults usually have a high survival rate, and young penguins don’t join the breeding population until they are two to three years old. Therefore, marked changes in the population are likely to occur over the macro-scale.
However, it is likely that the survival rate of the adults in 2011 was much lower than normal. Also, very few chicks were raised, and those that did leave the nest would have a slim chance of surviving if fish weren’t available close by.
It is likely that we will see a real decline in the population over a shorter time scale, especially if La Nina conditions continue.
But all is not lost for the Perth penguins; not yet, anyway. The colony on Garden Island did not appear to fare so badly. Their breeding participation and success was much better than that at Penguin Island – it usually is. This is probably because they feed in Cockburn Sound: just a short trip out the back door for these penguins. And for whatever reasons still to be identified, the fish stocks the penguins feed on in Cockburn Sound were apparently not affected by these high sea temperatures.
These penguins also nest in lovely cool limestone, unlike the penguins on Penguin Island who nest under bushes or in nesting boxes. So they are unlikely to be affected to the same extent by high air temperatures.
So this colony of penguins might be the saviour for penguin presence in Perth if we are unable to manage all the threats the penguins on Penguin Island are exposed to. We just need to maintain all the things that are responsible for them doing so well. We just don’t know what all of those are yet!
Watch a video about the Little Penguins.
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