Fascinating bird poop!!

The Golden-rumped Euphonia (Euphonia cyanocephala) feeding on mistletoe. Photo: Lou Jost/EcoMinga.

This picture took ten years of planning. The Golden-rumped Euphonia (Euphonia cyanocephala) is one of the most beautiful birds in our area, but it is hard to see and hard to photograph well. It is a mistletoe specialist; about 80% of its diet consists of mistletoe berries. Its digestive tract is much simplified compared to other birds, so that a mistletoe berry passes through them in just 7-8 minutes (compared to 15-20 minutes for unspecialized birds). These mistletoes, like their temperate-zone relatives, are parasites on trees and shrubs, usually high off the ground, so the euphonias which feed on them are usually out of photo range. Another challenge is that mistletoes are sparsely distributed here, so the euphonias have very large territories and don’t spend much time in any one area.

But these euphonias are so beautiful! So when I was building my house ten years ago, I planted a good host tree for mistletoes next to my kitchen window. Five years ago it was big enough to start hosting mistletoes, so I planted some mistletoe seeds on its lower branches next to my window. Then I waited. After another five years, my mistletoes began to make fruits. Finally one day I was working on my computer when I heard the euphonia’s distinctive call. I grabbed my camera, snuck up to the window, and waited as a male euphonia worked its way down to the lowest mistletoe, right where I wanted it. I only had a few seconds, and all but one of the pictures were blurry. But I was happy.

Mistletoe seeds evenly spaced in the strand of sticky euphonia poop. Only one mistletoe seed is in each fruit, so these seeds are stuck together in the bird’s intestine. Photo: Lou Jost/EcoMinga.

After it left the mistletoe, it perched on a branch and wiggled its butt like an American football player doing a victory dance in the end zone after scoring a touchdown. I didn’t realize it at the moment, but it was actually wiping its butt on the branch to remove the stringy poop it had just made. The poop is a remarkably long (12-15 cm) transparent sticky thread, with big green mistletoe seeds embedded in it at regular intervals. The dangling sticky seeds get stuck on branches, and the bird’s wiggling butt-wipes also plant some of the seeds directly on the branches of the host. The remarkable structure of the poop is especially surprising considering that each mistletoe berry contains only one seed. The glue in the berries (viscin) joins the seeds together into these long chains inside the bird’s intestines!

The top seed in this chain of poop has stuck to a host branch and may produce a new mistletoe plant. Photo: Lou Jost/EcoMinga.

Three strands of euphonia poop on the tree with the mistletoe. Note the chains of mistletoe seeds embedded in the strands. Photo: Lou Jost/EcoMinga.

These strands of euphonia poop are well-known to indigenous people wherever these birds live, and indigenous words for “mistletoe” often refer to its origin from bird poop.

Lou Jost