Blog post by Steffen Oppel, Senior Conservation Scientist, RSPB Centre for Conservation Science
“Honey, I’ll be right back”. Maybe that’s what the croaky, wailing call of a Murphy’s Petrel means as it waddles from its shady nest 20 m down to the beach on Henderson Island, leaving its partner on the nest to incubate the egg. Once clear of the shrubbery, the bird spreads its wings and sets out to find food – in the most nutrient-deprived part of the South Pacific. New research published few weeks ago shows that these hardy seabirds routinely travel >12,000 km during a single foraging trip, leaving their respective partners on the nest for 3 weeks without a break or a snack.
Murphy’s Petrel sitting on a log on Henderson Island
During an expedition to Henderson Island in 2015, an RSPB team attached small GPS loggers to the tail feathers of Murphy’s Petrels while they were incubating eggs. Once the birds had returned from their journeys, the loggers revealed the extent of their enormous efforts in search for food.
RSPB Scientists Jennifer Lavers and Alice Forrest attaching a GPS logger to the tail of a Murphy’s Petrel
Henderson Island is in the subtropical waters of the South Pacific Ocean, half-way between New Zealand and Chile. Because the surrounding waters are fairly warm, there is very little food for seabirds. To grab a decent meal, Murphy’s Petrels therefore need to travel about 1500 km south-west to get to a cooler water mass where it is easier to find food.
Some of the birds spend a week or more in this area, before travelling straight back to their nest on Henderson. However, other birds – usually the ones that weigh less when they leave – embark on a massive loop that brings them close to the coast of Peru, 5000 km to the east of Henderson.
Foraging trips of Murphy’s Petrels from Henderson Island in the middle of the Pacific Ocean. The green land mass is South America. Blue trips are the trips going only south-west, red are the looping trips to the east.
In this recent study published in the journal Marine Biology, Thomas Clay and the RSPB team speculate that the big looping trips might be a clever adaptation of light birds. By travelling mostly downwind, the birds can get to distant foraging areas along the continental shelf, where they might be able to find more food without having to compete with too many other birds.
Although the birds on the looping trips gained slightly more mass (indicating that there was more food), there may be other disadvantages that prevent all birds from adopting this strategy. Unfortunately, it is currently impossible which of these strategies enables petrels to raise more offspring on Henderson Island: invasive rats that were introduced by people kill virtually all Murphy’s Petrel chicks within a matter of days. Thus, even the most amazing journey to find food yields currently no reward in terms of raising any chicks!
To help Murphy’s Petrels to raise chicks in the future find out more about Henderson Island restoration programme of the RSPB.