Seabirds foraging at sea face deadly threats from eating plastics and being caught up in longline fisheries bycatch, but a new study reveals their colour preferences play a big part in their vulnerability to these human activities.
The Honours study published in Animal Behaviour explored the colours seabirds preferred using different coloured baits, and how avoiding these colours in both fisheries and plastic ingestion contexts could prevent seabird mortalities.
"This is the first time seabird colour preferences have been tested while seabirds were eating the bait, rather than afterwards such as in bird vomit called 'boluses' or opening their stomachs after they had died," said lead author Elliot Styles, who completed his Honours at the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS).
"The problem with studying boluses and stomach contents is that we can't know what colours of plastic the bird had to choose from, or if only a few specific colour choices were available. But our new approach eliminates this problem, and it has the exciting potential to begin a new theme of seabird colour preference studies," he said.
The study team headed out to the waters over the continental shelf in southeastern lutruwita / Tasmania, where they offered wild seabirds baits dyed white, yellow, red, green, black or blue. They then recorded the order these were eaten in and by which species of wild seabird.
"We found that seabirds do have a preference for the colours of bait they consume, and the order that they consume them in. Overall, we found white was eaten more often than the other colours we tested, but blue was the least preferred," said IMAS ecologist and co-author, Dr Lauren Roman.
Across 117 trials at sea, two bird species mainly interacted with the study – Shy-type albatrosses Thalassarche cauta and Thalassarche steadii and kelp gulls Larus dominicanus.
"Both species showed a clear colour-preference order, favouring white first, yellow and red second, and green and black third – with blue the last choice," Elliot said.
"We also found that multiple species of seabirds being present affected how many baits were eaten by each species. For example, Shy-type albatrosses tended to outcompete other species like kelp gulls, eating their most preferred colours and leaving the 'scraps' for the gulls."
While blue-dyed bait has sometimes been used in global longline fisheries to reduce seabird by-catch, the Agreement for the Conservation of Albatrosses and Petrels (ACAP) released a statement in 2023 advising against using this method as there was 'no experimental evidence of effectiveness in pelagic longline fisheries'.
"With the results of our recent study, we've shown that blue-dyed bait may actually have a place in longline fisheries, so it's important for further studies to be conducted to confirm our findings," Elliot said.
"Studies using our method would help build the knowledge of seabird colour preferences, and this could inform decisions around the colour of items most commonly lost at sea, such as fishing ropes and nets, and even equipment like weather balloons which are usually white or grey."
"Weather balloons pose one of the highest risks to seabirds because, when they burst, the fragments can resemble squid on the ocean surface – which is a preferred meal for seabirds."
The study suggests that simply colouring weather balloons and other items in the less preferred colour, like black or blue, could reduce seabird mortalities from mistaking equipment or plastics adrift in the ocean as food.
"This data provides useful information on what choices seabirds make when foraging, with implications for both plastic ingestion and use of blue-dyed bait as a bycatch mitigation measure," Dr Roman said.
Cover by Elliot Styles, looking back on the south-eastern coastline
of the Tasman Peninsula from waters over the continental shelf.
