On a recent trip to Spain it was interesting to note how many butterflies there were near the tops of hills and mountains. There were a few swallowtails (Papilio machaon) and large numbers of cardinals (Argynnis pandora) and clouded yellows (Colias croceus) all feeding on plants high on the mountain.
The explanation for this is a phenomenon known as “topping out”. Topping out is a process where male butterflies try to out compete each other and get higher and higher up a hill or mountain in order to impress the females and mate with them.
