1. Habitat destruction and illegal logging in protected areas.
2. Massive drought in Texas two years ago that left few nectar sources for migrating Monarchs. Many Monarchs may not have reached the overwintering site because they ran out of fuel (nectar).
3. Spring 2103 was cold in the Southern states for a lengthy period and that may have delayed the northward migration.
4. The cold weather may have resulted in the loss of one generation. Typically the numbers of Monarchs in the first (migrating) generation are small in number. Subsequent generations increase in number. The generation that migrates south will be the largest. If the last generation is missing the migrating population will be far smaller.
5. Changes in agricultural practices have led to a decline in the population of all milkweed species in many areas of the midwest. One study estimates a 60% reduction in milkweed populations.
6. Agricultural practices are reducing the numbers of nectar producing plants that provide food to adults.
Our own observations at the Tippecanoe County Butterfly Encounter have noted similar declines. The spring weather in 2011 was very cool and we noted lower counts. To be fair, some of the lower numbers may have been due to longer development times and delayed emergence of the population. 2012 was a record low count: 2 Monarchs. It was a drought year with many 100 degree (F) days in the week prior. We saw some Monarchs early and a huge migration of Red Admirals but they appeared to pass through and not stop in the area. In 2012, Monarchs were reported in far northern Canada, unusually far north. We don’t know what limits the northern migration of Monarchs. Perhaps the warmer weather encouraged more movement north? In 2013, we saw more Monarchs, but numbers were far below median numbers.
Will Monarchs recover? We don’t know. We do know that habitat protection, steps to increase or protect milkweed and increased numbers of plants that produce nectar would be a positive step.