Several posts on this blog (here and here and here) have reported interactions between birds and our favourite lizards, most of which have involved predation (but see here). Here’s a slightly different twist on the theme.
Boal (2008), in a paper in the Journal of Caribbean Ornithology, described the response of a female Antillean Crested Hummingbird on Guana Island in the British Virgin Islands to an Anolis stratulus that got too close to her nest. Anyone who has watched hummingbirds interact with each other for even a little while (particularly around hummingbird-feeders) will know how vicious they can be, and it isn’t surprising that a nesting female wouldn’t hesitate in attacking a lizard likely bigger than herself.
Boal describes how the hummingbird returns to its nest to find the anole about 10cm from the nest, and proceeds to make “rapid darting motions” to chase the anole until it’s about a metre away from the nest. To evaluate whether this was a one-off behaviour, Boal placed another A. stratulus in a similar position near the nest and elicited a similar response from the female hummingbird. However, while the first interaction occurred when the nest contained an egg, the second interaction took place when the mother was brooding a four-day-old nestling. This suggests that the females are not simply guarding against egg-predation (predation on nestlings has been proposed but doesn’t seem to have ever been shown; do you think an anole would eat a four day old hummingbird nestling? I’m not sure). Boal proposes an interesting alternative:
“The perceived threat could be a risk to the stability of the nest; conceivably, a climbing anole could destabilize a hummingbird nest such that the contents are dumped”
If this explanation is true, such interactions must be pretty common in the hummingbird breeding season in places where they are sympatric with anoles. Have any of you witnessed anything similar?
This tarnishes my view of hummingbirds as the sweetest and cuddliest of birds! I don’t see why the bird should distinguish among potential threats to the nest – the presence of any animal, potential predator or not, could trigger a similar neural response, leading to similar behaviors whether there is an egg, a hatchling, or no baby at all. It might not be the correct terminology, but maybe spotting some types of animals in the vicinity of the nest falls into some sort of “equivalence class,” in turn stimulating similar neural pathways and, consequently, similar response behaviors.
Interesting observations. I’ve definitely never seen a hummingbird attacking a lizard!
Martha’s explanation mirrors exactly what I was thinking — perhaps anoles fall into a sign stimulus category that hummingbirds indiscriminately respond to with aggressive behavior when in close proximity to their nests. This at least seems plausible, given that other reptiles (i.e. snakes) are well-known nest predators.
Thanks for the post — very interesting!