Merlin and Long-winged Harrier co-operation

The South Oropouche Lagoon, located south of San Fernando, is an open marsh environment inhabited by several resident Long-winged Harriers (Circus buffoni) and, in the latter months of the year, a few Merlins (Falco columbarius). I have noticed Merlins and Long-winged Harriers forming (temporary) symbiotic relationships, probably best described as a form of commensalism. Typically harriers fly low over the ground searching for reptiles and small mammals. They are neither fast nor agile enough to chase and capture healthy birds that have taken flight. Only if a bird is on the ground (nesting, hiding or injured) will the harrier have any real chance. The Merlins on the other hand fly higher and dive at flying birds, depending on their agility and speed. Once a bird is on the ground however, the Merlin is unable to hunt.

Both in 2007 and 2008 I have witnessed Merlins flying above and alongside hunting harriers in the South Oropouche Lagoon. Typically the Merlins flew in circles above the harrier. As the harriers search for prey, smaller birds take flight to avoid the harrier, which brings them in range of the overhead Merlins. I have seen Merlins make kills several times in this way. And while I have not actually seen a harrier benefit from this, I have seen harriers chasing successful Merlins who, weighed down by their catch, are now slow enough to be overtaken and this gives the harrier a chance to steal their catch.

It will be interesting to see if this is repeated in the years to come and at other locations.