One of the more lovelier birds in west Mexico is the west Mexican endemic, the Russet-crowned Motmot (Momotus mexicanus), shown below with a cockroach.
It was my good fortune to watch a breeding pair provisioning their offspring from around the middle of June to the beginning of July. I took pictures and made videos. While doing this, I was reminded of something I read in John Terborgh’s book Diversity and the Tropical Rainforest.1 In his book Terborgh argues that one component of increased biological diversity in tropical rainforests as compared to elsewhere is a greater number of niches. One such niche created by the presence of large tropical rainforest insects is the large tropical rainforest insect eating guild of birds, exemplified by the motmots.
While this wasn’t the rainforest and the insects and other things brought back to the nest weren’t all big, it was nevertheless an interesting assortment of food items. Because motmots nest in burrows and the chicks are hidden away, I couldn’t see them receiving their meals. Suffice it to say, though, for a motmot chick a meal can be a real surprise!
Caterpillars are an important nestling food source for neotropical migrants. For the photographed pair of Russet-crowned Motmots, they were important too. At times it appeared that the pair identified a particular caterpillar host plant and returned to that plant repeatedly for the same species of caterpillar. The first of three caterpillar photographs is also further evidence that the eversible osmeterium (the yellow “horn-like” projection arising from just behind the head) of swallowtail butterfly larvae, while secreting substances that deter ant and other invertebrate predators, is relatively ineffective against vertebrate predators.2
The motmot pair also commonly fed their offspring adult cicadas and less commonly juvenile forms (the first photo).
Beetles too were important components of the nestling’s diet. In the early part of my observations, elongate beetle larvae like the one shown in the last picture were frequently brought back to the nest.
The adult pair also fed their nestlings an assortment of other animal foods including, among other things, ant alates, millipedes, crabs, snakes, frogs, and terrestrial slugs. The last photograph shows a bird with a vertebrate whose tail is missing although I can’t tell if it’s a lizard or young mammal.
Finally, fruit – particularly guamuchiles (Pithecellobium dulce) shown in the first photograph – was also an important component of offspring diet.
These photographs show that Russet-crowned Motmots feed their nestlings a variety of foods from locations as diverse as the crowns of trees to leaf litter on the ground. They also provide additional evidence that the assumed chemical defenses of things like papilionid larvae2 and millipedes3 often do not deter bird predation.
1Terborgh, J. 1992. Diversity and the tropical rain forest. Scientific American Library, W. H. Freeman, New York.
2Leslie, A.J. and M.R. Berenbaum. (1990). Role of the osmeterial gland in swallowtail larvae (Papilionidae) in defense against an avian predator. Journal of the Lepidopterists’ Society 44(4): 245-251.
3Enghoff, H., N. Manno, S. Tchibozo, M. List, B. Schwarzinger, W. Schoefberger, C. Schwarzinger, and M. G. Paoletti. (2014). Millipedes as food for humans: their nutritional and possible antimalarial value—a first report. Evidence-Based Complementary and Alternative Medicine (2014): 1-9. https://doi.org/10.1155/2014/651768. (see references therein).