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A monarch butterfly. (Credit: Chris Paparo)

With the passing of Labor Day, it is as if Mother Nature flips a switch and shuts down summer. The days are noticeably shorter. Winds begin to blow from the north, pushing in cooler temperatures and forcing local beach bums to vacate their favorite haunts. Not only do the beachgoers hightail it out of here at the onset of autumn, but so does much of our local wildlife.

Seasonal migrations are very common in the animal kingdom. The most noted of the local journeys is the one taken by the osprey. Osprey of the North Fork head to Central and South America every fall, returning the following spring. Although this is an extremely far distance, it is not hard to fathom how such a powerful bird can make such a flight.

And soon another winged animal, the monarch butterfly, will be making a similar trek. Weighing approximately half a gram, it seems very unlikely they could fly a single mile, yet they are about to embark on a 3,000-mile journey. If you think the distance they travel is incredible, wait until you hear their entire life story.

Every fall, monarch butterflies begin a southbound migration to hibernate in oyamel fir trees growing in the Sierra Madre Mountains of Mexico. Along the way, they feed on the nectar provided by autumn flowering plants such as seaside goldenrod. It is vital that they find enough food on this trip to not only be successful, but to store enough fat reserves to survive their winter hibernation.

Traveling only during daylight hours, monarchs will stop just prior to sunset to roost in tree tops to rest for the night. The number of butterflies in these roosts can be anywhere from just a handful of individuals to thousands. I have been fortunate to witness several huge roosts over the years and it is truly a magical experience. Butterflies will only stay at a specific roost for one night before continuing south at sunrise. During years with many butterflies, these same roosts will be used each night by the following day’s migrants. What is even more amazing is the fact that these roost sites are often used year after year, even though the butterflies that stay the night never return to it again. How do the next year’s migrating butterflies know where is a safe place to spend the night? This is just one of the many mysteries of the monarch butterfly.

Once at the Mexican wintering site, they will cluster together on the oyamel firs to aid in warmth. A single tree can have upwards of 10,000 butterflies clinging to it. Here they will use their fat reserves to make it through the winter.

Waking up from their winter sleep, these monarchs will begin a northbound migration to complete their lifecycle. After mating, females will search for the one plant that is necessary for the survival of her offspring, milkweed. After laying between 400 to 1,200 eggs, she will die, ending her long journey.

Four days after being deposited, the eggs will hatch and the newly emerged caterpillars will feed on the toxic leaves of the milkweed plant. The resulting diet makes the monarchs poisonous, which will hopefully deter most predation. Two weeks later, the caterpillar will be fully grown and will enter the next stage of its life, the pupa. Forming a chrysalis, the caterpillar will transform over the next eight to 10 days into the beautiful butterfly we are familiar with. Like their parents, this second generation of monarchs will travel north, however they are not as long lived. With a lifespan of only two to six weeks, they must complete the lifecycle by laying the eggs of the third generation. As their predecessors, they will continue to move north and with any luck will pass on their genes to the fourth generation. This cohort is special and very much different than their parents and grandparents. Hatching in early fall, food starts to become scarce as flowering plants begin to die back due to cold temperatures. Milkweed has already seeded and will not return until next spring. To survive, these butterflies will now make the same journey to Mexico that was taken on by their great-great grandparents the prior autumn. How these butterflies, which have never made this migration before, can return to the same wintering roosts in Mexico every year is another mystery that leaves researchers scratching their heads.

Monarch populations have declined dramatically over the last several years. Habitat destruction of the wintering grounds, pesticides, and herbicides (killing the vital milkweed) are all fueling this decline. The last fall migration roost I witnessed was during September 2012 in Hampton Bays. Since then, even spotting a single monarch has been extremely difficult. I am optimistic about this fall’s migration as I have been seeing more and more monarchs every day.

Although I have not personally found a fall roost on the North Fork, that does not mean they do not happen. Look for them in protected areas along the shore with lots of seaside goldenrod. Pine trees tend to be the tree of choice when selecting a roost site. The best time to scout for them is just prior to sunset or just after sunrise as they warm their bodies in the sun before continuing their journey to Mexico

Possible Places to Look

Indian Island, Riverhead

Mattituck Inlet, Mattituck

Orient State Park, Orient