Karen Oberhauser, Director of the Monarch Larva Monitoring Project, at the University of Minnesota has been studying this year's mass migration of Monarch Butterflies and is somewhat surprised by her own findings. Firstly, there aren't as many Monarchs as predicted and secondly, they seemed to have missed out a generation.
The Monarch migration is a relay-race; hundreds of millions of butterflies from the same generation move, lays eggs, die, leaving the next generation to complete the next leg until the whole population reach the upper range of their migration around the Great Lakes. However, this year the Monarchs left Mexico later than expected and as a result, to make up lost time, they skipped a generation as they moved up through the US.
This does not seem to have had any lasting impact as the Monarchs are now moving southward. It's going to be a journey of some 2,000 km but unlike the spring migration, they won't be streaming as one united front (like in this video) but filtering down in smaller pockets. Interestingly, the Monarchs can adapt to varying weather conditions and maximise their speed using wind currents. If there is a strong southward wind, the butterflies will move up into its stream to make the most of the prevailing current.
El Dia de los Muertos (The Day of the Dead) is 1st November and is when the locals from the forests of Central Mexico welcome back the Monarchs to their hibernating sites. We'll hopefully catch up with the Monarchs then.