First, that’s what my research project is about: little birds (Dark-eyed Juncos weigh about 20 g; that’s the same as about eight bite-size Frosted Mini-Wheats biscuits, or 1/4 of a single package of ramen) that are tough. They are tough because they can breed at sea level or high on a mountain—that’s a lot of variation to adapt to! The high-elevation ones are especially tough, since on the tops of mountains there is snow, often into June, and the juncos have a very short window in which to raise their chicks before it gets cold and harsh all over again in the fall. They are also tough, or will need to be, because of climate change. Patterns of temperature and precipitation are shifting, and species are shifting too, but not all at once and not in the same ways, which means that habitats are changing. Juncos will need to be tough to handle that.
Second, the title reflects one of the reasons I am passionate about birds: they are little, or if they aren’t little they are fragile in other ways* (hollow bones, long thin legs, etc.), and yet they constantly astound me with their toughness. They live in deserts or on ice sheets or they stay aloft over the open ocean for months at a time. Tiny birds will migrate across whole continents, twice a year. Hummingbirds are so delicate that they sometimes have to slow down their metabolisms overnight to keep from starving to death before morning—and yet hummingbirds are very successful, and can live more than ten years. Birds are awesomely tough.
*Exception: ostriches. They do not look fragile to me at all. Ostriches, this blog is not about you.