Aphenotypical: the House Mouse’s Dark Secret

MONDAY, 18 MAY 2020

When researchers at Marion Island began investigating why albatross populations were declining, they discovered something no one could have imagined. Dozens of birds had been scalped with raw wounds all around their crowns and necks. They were being eaten alive by – that’s right – mice. The inconspicuous house mouse had developed a taste for blood.

A wandering albatross parent shelters its chick from the rain Marion Island, where precipitation is very common.

A wandering albatross shelters its chick from rain on Marion Island. Photograph by Thomas P. Peschak, National Geographic.

Albatrosses are known to be some of the largest seabirds on the planet. With wingspans reaching about three meters in adulthood, these majestic creatures have had nearly no natural predators – until the accidental introduction of house mice. The critters were likely introduced to Marion Island some 200 years ago by seal hunters, but it wasn’t until 2003 that initial signs of mouse predation – on the rumps and wings of seabirds – were first recorded. In 2009, scalping attacks in isolated regions were noted for the first time. Six years later, infrared camera footage finally caught the mice in the act, and an island wide survey revealed that about a tenth of albatross fledglings on Marion Island had been scalped by mice, half of which were already dead.

With no natural predators of their own on this remote oceanic island, the mice have sought out these seabirds to nibble away at their flesh throughout the night. Part of the problem is rooted in global climate change, which has allowed more mice to survive through warmer winters, resulting in greater depletion of the mice’s usual prey, such as moths, weevils, and seeds. Unfortunately, the albatrosses lack an instinctual fear of Dracula’s best friends and do not retaliate against the mice. While attacks were initially targeted at the rump and wings, the thinner feather lining on the head means that scalping is now the preferred mode of attack by mice across the island.

A seabird chick making unwanted rodent friends. Photograph by Peter Ryan, Royal Society for the Protection of Birds.

Over the past decade, this invasive species has begun feeding on albatross and petrel chicks, which are routinely left in their unguarded, warm underground nest for months while their parents are busy fishing or prepping for photoshoots with National Geographic photographers. More recently, however, it has been shown that the mice have started to predate on adult birds, putting further pressure on the island’s endangered seabird populations.

Thankfully, BirdLife South Africa and the South African government have swooped to the rescue, having implemented a program to drop poisoned grain as bait in an effort to clear the entire island of mice by the end of 2021. The mission is not a simple one – pilots will need to navigate extreme weather and brutal wind conditions to drop the bait on every square meter of the island, with an area spanning over eight times that of Cambridge. From there, it will take two years before researchers can assess whether the program worked and the mice have stopped giving non-consensual scalp massages. Until then, all there is to do is wait.

References:

Caravaggi, A., Cuthbert, R., Ryan, P., Cooper, J., & Bond, A. (2018). The impacts of introduced House Mice on the breeding success of nesting seabirds on Gough Island. Ibis, 161(3), 648-661. doi: 10.1111/ibi.12664
Davis, J. (2018). Gangs of mice are eating seabird chicks alive on a remote Atlantic island. Accessed 9 March 2020.
Dilley, B., Schoombie, S., Schoombie, J., & Ryan, P. (2015). ‘Scalping’ of albatross fledglings by introduced mice spreads rapidly at Marion Island. Antarctic Science, 28(2), 73-80. doi: 10.1017/s0954102015000486
Jones, C., Risi, M., Cleeland, J., & Ryan, P. (2019). First evidence of mouse attacks on adult albatrosses and petrels breeding on sub-Antarctic Marion and Gough Islands. Polar Biology, 42(3), 619-623. doi: 10.1007/s00300-018-02444-6
Jones, M., & Ryan, P. (2009). Evidence of mouse attacks on albatross chicks on sub-Antarctic Marion Island. Antarctic Science, 22(01), 39. doi: 10.1017/s0954102009990459

Saving a remote island’s birds—by getting rid of its mice.

Anna Tran is a BlueSci contributor.