How low can they go? Hummingbirds can eat dilute nectars, but it may require more time on the wing.

Hummingbirds consume energy at the highest rate of vertebrates, using the calories they take in to rapidly flap their wings, keep their tiny bodies warm, and travel on the wing. There are over 350 species of hummingbirds, many competing over food resources to meet their high demands. While we humans need a balanced diet, the food hummingbirds most often fuel up on is nectar (sugar water produced by flowers)! Nectar quality can change based on season, temperature, and rainfall but hummingbirds’ limits feeding on them remain unclear. We wanted to know how dilute nectars can become before the payoff isn’t worth it and hummingbirds can’t or won’t drink them. To tackle this, we worked in six field labs spanning North and South America to measure the maximum rate hummingbirds can eat, and the nectar concentration where this maximum occurs. To put this in real-life context, we collected nectar from wild, hummingbird-pollinated flowers across Ecuador. There we also measured how much energy wild hummingbirds use each day. Armed with this, we could better understand what happens when hummingbirds feed on dilute nectars.

We found hummingbirds can eat a lot: over 2/3 of their body weight per hour! Across body size, when nectars got too watery, hummingbirds either slowed down their eating rate, rested more, or both. This usually occurred when the nectar was 6% sugar (or 94% water). While nearly three quarters of the nectar concentrations that we measured in the field were over this threshold, some nectars were still low quality. What’s more, a flower well-stocked with nectar may not be accessible if another hummingbird is monopolizing it and chasing away others! To meet all their energetic needs, a hummingbird that can access all the most sugary nectars would only need to feed for 2 hours over the course of a day—but a sub-dominant hummingbird forced to feed on low-quality nectar might have to constantly forage from dawn to dusk. As climate change intensifies and competition escalates, hummingbirds may find it harder and harder to drink from flowers that “hit the sweet spot.”

Cover Photo credit: Timothy Kenney/Burke Museum of Natural History and Culture