This week’s bird is the Inaccessible Island rail (IIR), named for the remote chunk of rock it calls home. It is the world’s smallest flightless bird, and for a long time scientists were baffled as to how a bird that couldn’t fly got way out in the middle of the south Atlantic. Because our understanding of the planet’s plate tectonics is fairly recent, 19th century naturalists came up with fun solutions like the bird had walked thousands of miles across now-submerged land bridges or my favorite, that it was a relic population left behind after Atlantis sank into the sea. Genetic testing carried out in 2019 showed it is closely related to the dot-winged crake and the black rail, relatives from North and South America respectively. The current theory is that the bird flew to the island, and like other birds that reached a paradise with abundant food and no predators, lost its ability to fly after arriving.

Although there are currently no predators on Inaccessible Island that could threaten the rail, it is considered vulnerable because of its small population and vulnerability to any predators which may be inadvertently introduced by visitors.

The IIR has several adaptations to its environment in addition to its lack of flight. It lays few eggs, a clutch typically only numbering two, and has a very low basal metabolic rate, measured in 1989 at around 60-68% of the expected rate for a bird of its size. Rather than continuing to paraphrase, please enjoy this excerpt on the relationship between basal metabolic rate, flightlessness, and the IIR’s unique environment.

“The scientists responsible for the study speculated that the low BMR was not as a result of flightlessness, which does not have this effect in other bird species but was instead the result of the rail’s island lifestyle. The island lacks predators and other competitors, and as such can be expected to be at full carrying capacity for rails. This in turn would favour energy conservation by the rails, resulting in small body size, low BMR and flightlessness. A comparison of flighted and flightless rails, including the Inaccessible Island rail, found that rails that lose the ability to fly also have low BMRs.”

IIRs have tiny terrotories, around 100-400 meters, and will defend them from other birds with calls, displays and fighting if necessary. The IIR has a slow and deliberate foraging style, apparently similar to a mouse, and our tiny new friend occupies a similar ecological niche on the island. It feeds on a variety of invertebrates and insects, including an introduced species of centipede. It’s nice to know that not every outside species is a disaster for native wildlife, sometimes it’s just lunch. IIRs build pear shaped nests out of grass or sedges, with the entrance at the narrow end of the nest. Both male and female IIRs incubate their eggs, and the partner not currently brooding will bring food to the other. Formatting is going to get weird from here on out. It has taken me about 90 minutes of wrestling with wordpress to get to this point. Something changed in the last couple of weeks and I can’t figure out what. I cannot seem to copy and past my essay, no matter how I try, without wordpress deleting it and replacing it with a new “spacer” feature. I really wanted to arrange a nice header for you all, but I am afraid to leave this paragraph lest it delete all my work AGAIN. I don’t understand what’s wrong, I don’t understand how to fix it, and frankly, I’m pretty bummed. I would prefer not to be forced into WPT retirement like this. But, you know, please have a good weekend. Momentary frustration is just that, momentary.

Links: https://tinyurl.com/2dk2np63, https://ebird.org/species/inirai1, https://tinyurl.com/at8ux43a, https://tinyurl.com/3ey7rva4