Anhingas

Yesterday, the river of raptors here in Veracruz was momentarily dwarfed by the river of Anhingas. In Cardel, Citlali, Lynn and I counted 'only' 3,001 Mississippi Kites, a number that would be astounding at any other North American hawk watch, but early September in Veracruz is easily dismissed as 'nothing much'. And indeed we saw more Anhingas than Mississippi Kites, which does not happen very often.

In Cardel, we ended up with a count of 3,622 migrating Anhingas yesterday. Like raptors, they are diurnal migrants depending on thermals for lift, and are often found kettling up and then streaming out in search of the next thermal. Unlike raptors, they tend to all move synchronized when riding a thermal, a character that serves as an identification clue at great distances.

The species is resident in the area, but resident populations are augmented with northern migrants during the winter. eBird's Anhinga filter insists that any count over a few hundred individuals is a "great number" that it wants me to confirm, but counters and visitors to the project know that it is by no means unusual to see more than a thousand Anhingas in just one day here.

Seasonal counts at the site during the period 1995-2004 yielded a seasonal average of 31,000 individuals (Ruelas Inzunza 2007), with the 2002 count being exceptional with 40,000 Anhingas counted, i.e. 20% more than the estimated entire North American population! Clearly, those estimates need to be updated. This count in Veracruz provides valuable data not only for population estimates but also for population trends.

Cited literature:
Ruelas Inzunza, E. (2007) Raptor and wading bird migration in Veracruz, Mexico: spatial and temporal dynamics, flight performance, and monitoring applications - Dissertation University of Missouri - Columbia.