Filed under Monarch Population Status | 14 Comments »
It was apparent as early as late May that the migration, and the subsequent overwintering population, was going to be much lower this year than in 2015-2016. The projections outlined in the Blog post of 7 July have largely come true. The one surprise has been the production of late season monarchs in Kansas, Missouri and North Carolina. There have been reports from each state describing sites with large numbers of monarch larvae defoliating patches of naturally occurring milkweeds and in some cases milkweeds in gardens. The numbers of larvae reported by observers in these areas exceed anything reported this season further to the north, where most monarchs are typically produced.
The timing of this production, along with summer observations of low numbers of adult and larval monarchs in these states, suggest a southward movement of reproductive monarchs in late July and early August – a possible manifestation of the little-understood late summer movement southward of monarchs that I’ve dubbed the “pre-migration migration”. How much this more southerly monarch production will contribute to the migration and the overwintering numbers remains to be seen. That said, it still seems likely that the area of trees occupied by monarchs in Mexico this winter will be similar to that measured in 2014 (1.13 hectares).