Swarm-raiding army ants- like toucans and spider monkeys- are iconic animals of lowland tropical rainforests. So much so that you might be forgiven for assuming that they are found only there.
But that’s not the case. New quantitative surveys reported in Insectes Sociaux show that the common swarm-raiding species Eciton burchellii and Labidus praedator actually peak at higher elevations over 1000 meters.
Abstract: Geographic and elevational variation in the local abundance of swarm-raiding army ants has implications for the population dynamics of their prey, as well as affecting the profitability of army-ant-following behavior for birds. Here, we analyze systematically collected data on E. burchellii and L. praedator raid rates from geographically and elevationally wide-ranging sites, from lowland to montane forests. We show that raids of each species, and of both species pooled, reach peak densities at intermediate (premontane) elevations. These patterns suggest that army ant swarm raids are relatively abundant in Neotropical montane forests. Therefore, a paucity of ant raids does not explain the absence of obligate ant-following bird species, particularly true antbirds (Thamnophilidae), from montane forests. As army ant raids are relatively common at middle elevations, opportunities exist for other montane bird taxa to exploit army ant raids as a food source.
While it isn’t news that the swarm-raiders occur in the mountains (I watched Eciton burchellii raiding at the foot of Machu Picchu once), it is something of a surprise that the best way to find them is to head for the hills.
source: O’Donnell, S., Kaspari, M., Kumar, A., Lattke, J., Powell, S. 2010. Elevational and geographic variation in army ant swarm raid rates. Insectes Sociaux, online early.