Date: 11/07/2010

Number: 2000

Large quantities of overnight roosts of migrating Monarchs in the National Park Joya La Barreta just north of the City of Queretaro, Qro. Mexico.

I enclose some pictures I took yesterday afternoon. As you will see there were thousands of Monarchs, particularly in one tree. The location of the natural park can be seen in the Google Maps here: http://goo.gl/maps/fkzW

As you can see if you click on the Earth button, there is a mountain ridge just south of the parking/picnic area of the park. There are lots of oak species and other large trees to which the Monarchs seem to be drawn to roost. During daytime, they travel fast above this ridge, pulling south, but at aprox. 5 pm, i.e. one hour before sunset, they seem to start communicating among themselves and chose spots to roost for the night. All of the roosts are in parts of the trees where the sun shines until it sets. We always wonder how they communicate, my personal theory calls for pheromones, as they flutter their wings rapidly after landing on the tree. This seem to draw more and more butterflies to the same spot. Fascinating.

We saw no Monarchs drinking nectar, as if they do not have time for that. In the area there are lots of wild Salvia species in flower, I am not sure if they are good nectar sources. Otherwise it is poor at this time of year. We are deep into a cold front right now, last morning we had -4°C (wind chill -8°C) and this is the 3rd night in a row we have strong frost at night. I suppose this does not affect the Monarchs too much as the days are splendid and sunny.


The altitude of this roost is about 2600m.

The last picture was taken from a spot the sun had left about 15 min prior to sunset, as you see they have wings closed.

Queretaro, QUE

Latitude: 20.6 Longitude: -100.4

Observed by: Gunnar
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