Saturday, September 14, 2013

Monarch Migration - No; Green Darner Migration - Yes!

A migrant male Monarch Butterfly - a rare sight this summer
Monarch Butterfly migration was a complete bust this season. My unofficial count for Monarchs flying through the nature preserve so far is around 4 individuals total. By contrast last year was amazing - thousands of the iconic species passed through during the late season peak bloom of goldenrod and asters. Of course, though an individual Monarch will make the epic journey to Mexico, it takes a number of generations for its descendants to repopulate the northern parts of its range.
A massive bloom of Asters and Goldenrod help fuel the Monarch's long journey

A lack of Monarchs this year shows that there are potentially serious problems on the breeding grounds in the US and Canada and/or on their wintering grounds in Mexico. Deforestation on their crucial wintering grounds is likely the main cause of their decline, but an increasing use of genetically modified crops in the US is being pointed to as  another significant factor. As herbicide tolerant crops can now be doused with herbicides like "Roundup", vital milkweed stands are disappearing - and with them the Monarch's livelihood.
Monarch caterpillar on a Milkweed seed pod in 2012 - we found no caterpillars in 2013
Milkweed is popular with other insects like this Swamp Milkweed Leaf Beetle
Milkweed Tussock Moth Caterpillars also munch on milkweed 
A migrant Green Darner Dragonfly perches along a meadow trail
While Monarch numbers have been low this year, the number of migrant Green Darner Dragonflies has been up sharply – and yes, the Green Darners do migrate. Around a dozen species of Dragonfly migrate in the US. That's especially interesting considering that less than 50 species out of over 5,000 species of dragonfly in the world are known to migrate.
Dozens of Green Darners perched alongside the meadow trails
The dragonflies were zigzagging back and forth over the trail  catching prey
At the nature preserve, on several trails that pass through large meadows, Green Darners line the sides of the trail and take to the air when someone walks too close. The darners blend in so well with the vegetation that it’s really difficult to pick one out until it takes flight. Given that, it was somewhat frustrating trying to get pictures of them as they perched. The swarm of darners flying over the field was also also hard to photograph. There were at least 50 of them zooming back and forth all over the meadow, scooping up smaller flying insects on the wing.
The female Green Darner lays eggs into the water while the male clasps her neck
A shed dragonfly nymph exoskeleton still hangs onto a leaf  
I know that the 2013 breeding season was excellent for dragonflies locally, but a healthy number of migrants tell us that they also did well on breeding grounds in the Adirondacks and Canada. This year, the early part of the breeding season was particularly wet in parts of the Northeast, and so it makes sense that these wetland dependent insects would've fared well. Pools of water that are rich in insect larvae (including mosquito larvae), but not rich in predatory fish are ideal for dragonfly larvae to develop in.
A Green Darner is more slow to take off on a cool morning
Other dragonfly species like this Black Saddlebags were seen with the darners
Meanwhile, Red Saddlebags were still breeding at the Frog Pond
Dragonfly migration is very similar to bird migration. Just like most migrant birds, the dragonflies don’t make their entire journey in one “bound”, instead they utilize migratory stop-over sites. Apparently our habitat-rich nature preserve is one such site – at least it is this year. Since the dragonflies use the same migratory flyways that birds do, at some hawk watch sites across the eastern US, this year there should be thousands of Green Darners passing over. It’s thought that American Kestrels especially take advantage of these dragonfly swarms as a source of food to help fuel their own southward migration.

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