Monday, April 5, 2010

The Spring Migration in Phoenix

Last Friday, April 2, a male monarch butterfly was spotted at the Desert Botanical Garden in Phoenix 2:15 in the afternoon. It was a sunny day with temperatures in the low 70's. Earlier we had a few days of strong winds from the south that could have thrust him into the Phoenix area. Monarch butterflies love to hitch a ride on thermals and gust fronts. While we have no way of knowing for sure that this is the case, it is interesting to record and note.

If you look closely at the color of the monarch butterfly in this picture, the orange color is rich and the wings look new. This male is likely a freshly emerged monarch rather than one that traveled from overwintering sites in Mexico or California. In comparison, the female spotted laying eggs on March 15 was faded and a tad tattered from her journey. Of course this raises the question, WHERE did he emerge? This monarch butterfly likely came from the first generation of a monarch that either overwintered nearby in Arizona, or flew from Mexico or California and laid eggs on available milkweed.

On Friday the male monarch was "patrolling" the milkweed in the Herb Garden. Male monarchs will often fly over milkweed patches looking for a female mate, driving off other butterflies to protect his field. In this picture he took a rest to sun on a plant for a moment, but was quickly back in the air cruising the thicket. Its interesting to just sit back and watch their flight pattern that resembles a jet in a flight hold over an airport, circling around and around. Today I returned to see if he was still at DBG, but he was gone, likely moving north or northeast. In fact I didn't see a butterfly of any kind that morning despite the sunny and delightful temperatures. So often what we see is a matter of timing.

We watched the three monarch eggs deposited on a milkweed plant at the Desert Botanical Garden on March 15.  One egg developed into a tiny caterpillar with its large dark head, but was gone two days later. The other two eggs never developed. Monarch eggs have a high mortality. Studies indicate only one egg of ten becomes a monarch butterfly. The numbers are even lower if more predators are present.

Several milkweeds are beginning to bloom: Tropical Milkweed (Asclepias curassavica), Narrowleaf Milkweed (Asclepias angustifolia), Pineleaf Milkweed (Asclepias linaria). Desert Milkweed (Asclepias subulata) will likely bloom in the next few weeks savoring the warmer temperatures and also extending the milkweed availability for migrating monarchs.

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