About 50 species of Neotropical birds regularly feed on arthropods that try to escape from army ant swarms. Much of this ant-following behavior is still of most of these ant-following birds is still unclear, encouraging further research. Furthermore, the army ant species Eciton burchelli as well as ant-following birds are endangered: forest fragmentation and isolation have a strong negative impact on them.
In a montane rainforest in the northwest of Ecuador, I studied what type of ant-following behavior (obligate or opportunistic) different ant-following bird species show. To determine this, the first approach was to study their use of vocalizations of other ant-followers to track swarms of Eciton burchelli. It was hypothesized that only obligate ant-following birds find swarms by tracking the vocalizations of other obligate ant-following birds.
To test this, recordings of specific species were played back to see if they attract ant-followers (if they do, the species can be considered as obligate) and which ant-followers they attract (the species that are attracted can also be considered as obligate).
The second approach was to estimate territory size and travel distance of different ant-following bird species to potential army ant raids. As obligate ant-following birds track swarms of several army ant colonies per day, it is hypothesized that they have to travel greater distances in order to find the swarms and therefore have a bigger territory than opportunistic ant-followers.
To combine studying the response of the ant-followers to playback with studying territory size and travel distance, playback experiments were conducted at different locations. In this way, the individual ant-followers that were attracted to the playback were also used to estimate the territory size and traveling distance of their species.
Results showed that the Bicolored Antbird, the Zeledon’s Antbird and the Plain-brown Woodcreeper are obligate ant-followers, although the Bicolored Antbird did not seem to use vocalizations to track ant swarms. The Esmeraldas Antbird, Chestnut-Backed Antbird and Spotted Woodcreeper are considered as opportunistic ant-followers, although the Spotted Woodcreeper seemed to use vocalizations to track ant swarms.
For accurately estimating territory sizes and traveling distance the research area of 15 ha was found to be too small. For further studies on territory sizes and traveling distance, using radio tags and a bigger research area is recommended.