>> it's the kind of bird that hides deep in these swampy mangrove jungle gyms on isabela. how can you tell it's amman donndon -- abandoned from here? okay. >> oh, the mangrove finch. did you hear that? toot, toot, toot. >> that's a good sign all right. they say completely hidden during our hike. but here's footage from francesca's team. not only are these birds threatened by rats but in the 1950s a random load of cargo brought a certain kind of fly to the galapagos, a fly that feeds on the little beaks of baby finches. >> it's sort of like a horror story really, that the fly lies its eggs in the nest, then the first larval stage enters the nasal cavities of the nestlings, so a lot of the birds die.