>ISSUE: Mass deaths of Swainson's Hawks are occurring in Argentina due to
>insecticide spraying
>
I would like to add a bit of info on Swainson's Hawks, based on what
I learnt while in Argentina a few years ago. First of all, the numbers being
retrieved dead are worrying. This is a lot of dead hawks, birders should be
very concerned about this issue.

>........ In addition the area affected by sprays is larger that
>his study area. Thus he believes his count of 3909 hawks may represent
>20,000 dead hawks in this region of Argentina. Most (90%) of the dead hawks
>were adults (ie. the breeding population). The winter range of the
>sub-adults is unknown.

In fact, the wintering range of juvenile Swainson's Hawks is known.
Almost all of many thousand Swainson's Hawks that I observed in eastern
Buenos Aires province were juveniles. I saw only two adults in two seasons
of observations there, both were rufous morph adults. The largest flock of
juvenile Swainson's Hawks over my study area was estimated at 5000
conservatively, but likely was twice that size!! Swainson's Hawks were
present between mid November and up until mid January (when I left), so they
were indeed wintering in the area. My field site was roughly 300 km south of
the city of Buenos Aires, near the town of San Clemente del Tuyu, right on
the Atlantic coast. It is roughly 650 km straight east of General Pico where
the deaths are being reported. My impression is that juvenile
Swainson's Hawks winter in the wet Pampas of eastern Buenos Aires province
while the adults winter in drier areas to the west, south and northwest. I
have seen adult Swainson's Hawks as far south as the Valdez Peninsula in n.
Patagonia. Their wintering range is large.
In my study area, Swainson's Hawks fed almost exclusively on the
migrant dragonflies Aeshna bonariensis and Aeshna confusa, not grasshoppers
or locusts. These dragonflies arrive in massive swarms during cold fronts,
the hawks follow the swarms and feed on them on the wing. Large numbers of
hawks were seen only when the dragonflies were going through, their numbers
diminished quickly afterward as the swarm finished passing over our area. I
was able to conclude that 92.3% of the prey in regurgitated pellets were
dragonflies, with most of the rest made up by ground dwelling insects. The
San Clemente del Tuyu area is strictly ranching country, there is no crop
agriculture in the area and I assume no spraying of pesticides.
>
>The study area is at the junction of the three states of Cordoba, Buenos
>Aires, and La Pampa. This is only a small portion of the winter range of
>Swainson's Hawks and a small portion of the cultivated agricultural land in
>the grasslands of Argentina. The geographic extent of the problem is
>unknown.

If my info can be generalized to the eastern Pampas, then perhaps
the hawks are relatively safe from pesticides during their first winter (as
juveniles). However, more cencuses and studies should be conducted to
determine if this is true.

For those that are interested, this info was published as: Jaramillo, A.
1993. Wintering Swainson's Hawks in Argentina: food and age segregation.
Condor 95: 475-479.

Let's work to get this problem resolved.

Alvaro Jaramillo "You are better off not knowing
Half Moon Bay, CA how sausages and laws are made"
alvaro at quake.net Otto von Bismarck,
but I saw it in a fortune cookie!

http://www.quake.net/~alvaro/index.html