Monday, August 1, 2011

Zone-tailed Hawk: rare or not?

Today's post looks forward a little to what I'll be doing the next three months: participating in the world's biggest hawk migration census, in Veracruz, Mexico. It will be my third season there. One of the raptors that migrates through Veracruz is Zone-tailed Hawk. The first ones usually show up there late August. It then becomes an almost daily species in September. In Veracruz, the peak of their migration is during the last week of September and the first week of October, when double-digit days are regular.

Looking at the Veracruz River of Raptors dataset from the last 9 years, an increase from season totals of around 150 in the period 2002-2004 to totals around 250-300 for the period 2005-2010 is evident (source: Earlier, during the period 1995-2004, the season average for Zone-tailed Hawk at the site was 117.4 (Ruelas Inzunza, 2007). At least as a migrant in Veracruz, this bird clearly appears to be increasing.
Yearly totals Zone-tailed Hawk at fall migration counts in Veracruz, Mexico (2002-2010) [source:]
Only northern populations undertake a southbound migration, and this increase at a major raptor migration census station likely reflects an increase of this northerly, migratory population.

These photos of an immature zone-tail were taken last month in El Salvador, where Zone-tailed Hawk is a fairly common permanent resident species. Like White-tailed Hawk, this is a widespread yet little studied species: the BNA account (Johnson et al. 2000) calls the status and distribution south of the U.S. "problematic", meaning little is known of those Central and South American populations. Indeed, their map seems incorrect: it shows southern Mexico and all of Central America as "winter only", with only a couple of small, isolated breeding locations in Nicaragua and Costa Rica. Big question marks on the map highlight this 'problematic' aspect of our knowledge of this species' distribution. Howell & Webb (1995) show a similar map, including the question marks, with the range for most of Central America as "winter only".

The most detailed and up-to-date, but still incomplete, information on the status of this species in Central America can be found in the species account of The Peregrine Fund's Global Raptor Information Network (or GRIN). This is what they have for Honduras:

Honduras: Probably a rare resident in the interior highlands. Breeding is as yet unconfirmed, and all records are from the winter months (Monroe 1968), except for one seen in April along the road from Tegucigalpa to Bonanza (Jones 2004). Jones (2005) noted that this species was being reported on average only once every two years on the Caribbean slope of Honduras, but by 2006, it was being reported more frequently (one to three times per year) (Jones and Komar 2006). Most likely, this reflects better coverage, rather than an actual increase in the number of zone-tails in the region.

My own impression is that this bird is an uncommon to locally fairly common resident throughout Honduras, including the lowlands. I have seen and photographed a pair with nesting material in the southeastern province of Choluteca in January 2010. On the campus of Zamorano University near Tegucigalpa, where I have been these past couple of weeks, I see adults and immatures almost every day. I have also seen this species elsewhere in Honduras, and am surprised to find how little has been published on the distribution of this species in Central America, and how rare it is reported to be.

Is this species really rare in Central America, or has it been under-reported? And if it's not that rare, is that a recent trend?

Cited literature:

Global Raptor Information Network:
HMANA count data:
Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford Univ. Press, New York.
Johnson, R. Roy, Richard L. Glinski and Sumner W. Matteson. 2000. Zone-tailed Hawk (Buteo albonotatus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
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.

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