Fishing nets pose a serious risk to the survival of penguin species, according to a new global review of the toll taken by “bycatch” from commercial fishing. Fourteen of the world’s 18 penguin species have been recorded as fishing bycatch.
Among the species under threat are Tasmania’s little penguins and New Zealand’s yellow-eyed penguins, as detailed in a review, published in the journal Endangered Species Research.
The review shows the level of bycatch is of greatest concern for three species: Humboldt and Magellanic penguins, both found in South America, and the endangered New Zealand yellow-eyed penguins.
On New Zealand’s South Island, yellow-eyed penguins are down to fewer than 250 nests. Previous population strongholds have declined by more than 75%. Conservative population models predict local extinction of yellow-eyed penguins by 2060, if not earlier.
Penguins are among the world’s most iconic and loved birds, despite the fact that many people never get to see one in the wild. Indeed, the opportunities to do so are diminishing, with ten of the 18 penguin species threatened with extinction. After albatrosses, penguins are the most threatened group of seabirds. And, like albatrosses, bycatch is thought to be a serious issue for some species.
On land, many penguins are now well protected, thanks to the efforts of conservation researchers, government agencies, community groups and tourism operators. Where many penguins were once vulnerable to attack from introduced predators, or to habitat loss from farming or development, today the biggest worry for many penguin chicks is how to get more food out of their parents.
But below the waves it’s a different story. Over thousands of years, these keen-eyed seabirds have evolved to catch food in the depths, while avoiding natural predators such as seals and sharks. But they cannot see the superfine nylon fishing nets invented in the 1950s which fishers now set in penguin foraging areas.
Little penguins, whose scientific name Eudyptula minor literally means “good little diver”, typically forage in the upper 20 metres of the ocean, with each dive lasting about 90 seconds. The larger yellow-eyed penguin – Megadyptes antipodes, the “big diver of the south” – prefers to hunt on the seafloor some 80-90m down, holding their breath for 2-3 minutes before coming up for air. If they do not encounter a fishing net, that is.
Gillnets (also called set nets) in particular are very dangerous for penguins. These nets are set in a stationary position rather than being dragged through the water. They are designed to catch fish around their gills, but can just as easily snare a penguin around its neck.
If it gets tangled in a net, a penguin will panic and drown in minutes. In Tasmania, nets with more than 50 drowned little penguins have been found washed ashore. Other penguins are found on beaches with characteristic bruising from net entanglement around their necks.
When a penguin is killed at sea, this has knock-on effects back at the nest. The chicks will die of hunger or fledge underweight, with little chance of surviving their first year at sea.
The breeding partner left behind will probably skip a breeding season; some penguins never find another partner after losing their mate. I have seen them calling plaintively from their nest, or even going down to the shore in the evening to look out to sea, before returning to their nest all alone.
In New Zealand, the endangered yellow-eyed penguin is declining. Current population models predict their extinction on the New Zealand mainland by 2060, or potentially even earlier. Yellow-eyed penguins are facing many threats mostly because they are simply living too close to humans.
Whereas threats on land are reasonably well managed, threats at sea need urgent attention. Marine habitat degradation by industries that damage the seafloor will take decades to recover. Similarly, pressures from climate change will not have a quick enough fix to save yellow-eyed penguins from local extinction.
There is one thing, however, we can change immediately: the needless death of penguins in fishing nets. This will give already struggling penguin populations a bit of a breather and maybe even the resilience required to deal with the many threats they face in their daily fight for survival.
Judging by the number of penguins washed ashore with net injuries, many fishers simply discard penguins’ carcasses at sea rather than reporting bycatch or working towards solutions to mitigate it.
Do we really want penguins to drown for our treat of fish and chips? Less destructive fishing methods are available that do not cause penguin bycatch and the death of other protected species.
But these more selective fishing methods would require fishers to change gear, which costs money. Currently, there is very little legal or commercial incentive for fishers to do anything about penguin bycatch.
But there are a couple of things you can do. Please do not just buy any fish with your chips – ask which species it is and how it has been caught. You can use a sustainable seafood guide, such as New Zealand’s Best Fish Guide or Australia’s Sustainable Seafood Guide. That way you can help the penguins snag a safe fish supper of their own.
Crested pigeons are a common sight in many Australian backyards, and are noted for the rapid trilling sound they make when they take flight.
In our research, published today in Current Biology, we show that these sounds are produced by feathers in the wings that have evolved to communicate about danger.
These sounds were long suspected of being produced by the wings, so we used high-speed video and acoustic recording to investigate this.
The key finding is that a pair of unusual primary flight feathers, half the width of the others, produce a high-pitched sound as the wing pushes down through the air. This sound is a critical part of the alarm signal that warns the flock.
No other related pigeon species has these unusually narrow wing feathers. The narrowness of these feathers, known as the the 8th primary feathers, suggests that they have evolved to produce this high-pitched sound.
Feathers to the test
We discovered that the 8th primary feathers produce the high-pitched sound, by trimming pairs of feathers and recording the sounds of pigeons fleeing. But we were also interested in how trimming the 8th primary feathers would affect the response of other crested pigeons that heard these modified fleeing sounds.
We developed a speaker set up that let us broadcast the recorded fleeing sounds of birds from the side of a vehicle. We would then drive next to pigeons foraging in parks and on nature strips around Canberra, and broadcast one of the recordings at random.
When we played recordings of crested pigeons with both the 8th primary feathers removed, the birds looked up, but almost never flew off.
Our suspicions were correct – this unusual pair of 8th primary feathers and their high-pitched sound were necessary for warning other pigeons to flee.
So what about the neighbouring 9th primary feathers? We discovered that these produce a low-pitched sound during take-off.
When we played recordings of crested pigeons with both the 9th primary feathers removed, the birds flew off just as often as if they’d heard an alarm. These feathers were not necessary for warning flock mates.
All in a flap
Signals evolve when the creature producing the signal and the one responding to it both benefit.
Crested pigeons that see predators can benefit by inciting the rest of the flock to flee with them, much like redshanks and Belding’s ground squirrels, whose coordinated fleeing confuses predators.
The benefit from communication to every individual could explain why the 8th primary is so unique – it has evolved to exaggerate the sounds of fleeing to trigger a coordinated response.
While these pigeons always produce some sound when they take off, the sounds produced when fleeing danger are distinct. They are louder and have a higher tempo.
Footage from high-speed video cameras showed that fleeing pigeons flap faster when trying to escape a threat. Flapping faster speeds up their escape and it also increases the tempo of the sound, thus transforming the take-off sound into an alarm.
While these differences in the sound can be quite subtle to the human ear, crested pigeons are able to respond to them in about a third of a second. (Can you tell the difference between these two sounds?)
All animals produce some sound as they move, and these sounds are intrinsically informative. They tell the listener where the individual is and how it is moving. This is in stark contrast to the sounds produced by our voices, which are not the result of specific actions.
The same is true for animals: vocal calls are notoriously unreliable, even being used deceptively to steal food. Africa’s fork-tailed drogos, for example, often use their own, and even other species, vocal alarms to scare competitors away and steal their food.
Non-vocal sounds, by comparison, are unable to be faked. If a crested pigeon flees it cannot help but warn its flock mates, just as it cannot warn its flock mates without fleeing.
This means that these non-vocal alarms are a very reliable indicator of danger – and, more broadly, that non-vocal sounds produced by movement are intrinsically informative and so are likely to evolve for communication.
Other feathered messages
Crested pigeons aren’t the only birds that use their feathers to communicate. We know of several other pigeon species that produce conspicuous sounds with their wings that are just waiting to be investigated, such as the Spinifex pigeon.
Mourning doves and zenaida doves from the Americas also make sounds, that appear to be produced by their wings, that warn their flock mates of danger.
Non-vocal acoustic signals are used in many other groups to maintain territories and attract mates – manakins and hummingbirds being the most widespread examples.
It appears that non-vocal acoustic communication is much more common than most people thought, and so we hope a new generation of curious people are inspired to listen closely to the animals around them and discover even more of these unusual signals.
The fourth Aussie Backyard Bird Count has just ended, with nearly 2 million birds from 635 species submitted to the BirdLife Australia app. The count, which is in its fourth year, has created a national database of birds found in our backyards.
We don’t know yet exactly how many people participated this year, but more than 60,000 people submitted checklists in 2016. Participants span the whole country, though participation is highest in our urban areas. By surveying our backyards (rather than “good” bird spots), these citizen scientists provide ecologists – like me – with information from urban areas we would not otherwise sample.
This includes data on a range of common bird species that are not frequently analysed because these species are believed to be secure. One of the most surprising results is a decline in the frequency of occurrence of the laughing kookaburra across southeast Australia.
Everyone has a bird story – and fortunately for ecologists, everyone is willing to share them. With 85% of Australia’s population living in cities and towns, birds are an important connection to our natural environment.
But birds are also good environmental indices. They’re generally easy to measure, they respond quickly to environmental change and we know a reasonable amount about the ecology of most species.
Between 1998 and 2014, BirdLife Australia volunteers collected a significant amount of data. This was used to develop a terrestrial bird index in 2015 – a bird “Dow Jones” to track our biodiversity. It was here that the decline in kookaburras was first identified.
The data were drawn from BirdLife Australia’s ongoing atlas project, now called Birdata. However, there are biases in this data set, as people obviously like to go birdwatching where they will see more birds. This may inflate the frequency of encountering some species and decrease the chances of encountering others – particularly rare and cryptic species.
For the last four years, we’ve asked volunteers to add to this data by counting birds around their home for a week in October, when many birds are highly active and visible. These counts complement the data already available in Birdata by allowing access to backyards across Australia, which are generally poorly represented in the larger data set.
While there are still limitations in the Backyard Bird Count data, such as the risk of mis-identification, for common species like the laughing kookaburra we can generally be confident that the identification is correct. Even if the same bird is counted multiple times, our models report only a species’ presence or absence, so inflated numbers don’t affect the trend.
Are kookaburras really declining?
The below figures show modelled trends for the kookaburra across metropolitan Melbourne and Sydney. These figures are derived from the volunteer-collected Birdata, much of which comes from green spaces and remnant vegetation in these landscapes.
I wondered whether these declines are true changes in the populations, or reflect a change in the way kookaburras are using the landscape, possibly moving into the matrix of urban backyards that just don’t get surveyed. Looking solely at the backyard count data, I found similar trends in the reporting rates of kookaburras as those in the models, supporting that this decline is at the population level. What started out in 2014 as a way of engaging the broader community with their birds is now collecting useful ecological data.
Further exploration of the ABBC data across other capital cities found some interesting things. In both Perth and Hobart, where the kookaburra is considered an introduced species, the birds are recorded more frequently than in Melbourne and across the ACT. In Perth, increases in 2016 compared to previous years suggest an increase in the species there.
While three years does not make a trend, Aussie Backyard Bird Count data from heavily urbanised areas suggest we are seeing a decline in this iconic species in the eastern capitals. Likely reasons for this are the loss of nesting hollows and possibly reductions in the availability of prey as we increasingly modify our urban landscapes. We don’t really know as this is not an area that has been researched.
We need citizen scientists
Collecting enough data (especially from the backyards of towns and cities) to detect these kinds of changes can be an overwhelming task. This is where citizen science programs like the Aussie Backyard Bird Count can help.
As well as helping ecologists track large-scale biodiversity trends, it also gives people the chance to connect with their natural environment and gain a greater appreciation of our unique fauna.
As with all citizen science projects, there are limitations in the data being collected. However, the Backyard Bird app has been designed to make counting as simple and standardised as possible, providing confidence in the tally of common and “iconic” species, and filling in the gaps found in other data sets.
The good old kookaburra is neither rare or cryptic. If anything, if people are seeking out “good” bird habitat to survey we would expect that kookaburras would be one of those species subject to inflated reporting. But this is not what we encountered.
If we are starting to see declines in species that we have traditionally considered secure, what does this mean for those that are already at risk? Once all the data from the Aussie Backyard Bird Count have been collated and vetted we will continue to explore the developing trends in Australia’s urban birds. Increasing engagement and awareness in our communities can help ensure our backyard birds are still around to count next year.