During the past month I have twice written articles about our well known Ruby-throated Hummingbirds and their remarkable energetic lifestyles with particular interest directed to their endurance in making long flights. Last week I discussed the possible scenarios for their return to the tropics for the winter. Whether they return to their wintering grounds over water or over land, they are very difficult and energy-consuming trips for birds that weigh only a few grams each. The rubythroats do not do anything different than their larger migrant bird relatives when traveling.
In the insect world only a few species attempt to migrate over long distances, Monarch butterflies and Wandering Glider dragonflies. As adults, insects have very short life spans ranging from a few weeks to a few months. For the sake of brevity, I will only compare the Monarchs’ lifestyle and travels with those of birds. The life span of birds is not well documented; however, normally songbirds live for several years compared to many decades for larger raptors and seabirds. Most Monarchs live for shorter periods, typically a few weeks during which they need to find a mate to propagate their species before dying.
The short life cycle for Monarchs is controlled by reproductive hormones that dictate their short lifespans. In the fall, the last generation of Monarchs to hatch have a built-in delay in the reproductive hormones that allows the butterflies to live for an additional five to six months before the hormones activate. This increased term of life allows these butterflies to migrate from Canada to Central Mexico to overwinter in the mountainous Michoacan region of Central Mexico. The Monarchs have built-in instincts that funnel them southwestward through Texas and the Hill Country and southward into Mexico.
The Monarch migration is not that different from that of migratory birds other than that the birds can cover the long distance in much shorter time periods. Along the southward migration routes the butterflies are helped by northern winds to help push them southward in the same fashion as experienced by the birds. One big difference between birds and butterflies is that the butterflies do not travel at night. Another factor favoring birds is that they can store up fat to allow them to fly longer distances without feeding. The butterflies often pick roosting sights along their journey to spend the night.
Like birds, the butterfly internal alarms signal them when it is time to head northward in the spring. Unlike birds, the butterflies’ alarm also triggers the insect’s reproductive hormones to start their mission to head northward in search of milkweeds to serve as larval food plants for their offspring. Slowly the generational “leap-frogging” continues until the butterflies reach their northern limits in our northernmost states and southern Canadian provinces. The birds reach their breeding grounds in the same time frame as one of the Monarch’s generations covers its leg of the northward journey.
Over the past years, the Monarchs have taken some hits that have caused their numbers to dramatically drop. Increased habitat loss in Mexico and increased use of pesticides in the United States has had negative impacts on the numbers of these large black and orange butterflies. Occasional winter storms have also reduced their numbers in Mexico, and our prolonged drought in the United States has limited milkweed production for the butterflies to utilize along their migration route.
If you are a gardener, please consider adding a variety of milkweeds to your mix of plants for your garden next spring. Some milkweeds are sold in nurseries, but another solution is to collect milkweed seeds and sow them in any meadows or open space on your property.
Antelope-Horn, Texas Milkweed, Hierba de Zizotes, and Purple Milkweed Vine are a few native plants that could boost the available larval food sources for the Monarchs next year. Go on the internet to learn about Monarch Watch and other initiatives to help save these beautiful butterflies. As we help our endangered birds, we need also to show these butterflies the same compassion.