Monarchs On The Wind
Mid-August last year I returned to a familiar late summer haunt, a picnic table on a dune overlooking the northern tip of Lake Michigan. I go there each August to do my table-top survey of one of the world’s most beautiful insects—the Monarch butterfly. Monarchs have always been special to me, even as a little boy I would chase them through fields to get a closer look. Now as most time lies behind me my attention has returned to the butterfly of my youth. Who doesn’t want this miraculous flapper to draw future generations of kids to the same fields.
So I count Monarch butterflies as they fly over or past me, heading westward down the beach toward their destiny—Mexico. My survey is rather crude, a time-count that I made up. All I need is my notebook, pencil, watch and a beer to survey the fall flight. I measure the interval, in seconds, between animals to get a long time average. In the mid-2000’s the flies would pass my position every 10-15 seconds if I hit the peak of migration at a spot six miles east of Manistique. Peak numbers were late in 2012, September 1-2. I counted butterflies on both days, with the same disappointing results-a fly every 45 seconds. Could the butterfly numbers have fallen by 70% in just 5 years?
My answer came from an internet search of the website –Monarch Watch. This group of butterfly conservationists is performing wonderful educational and research work in an attempt to help the Monarch. They are involved with the World Wildlife Fund and the science people from Mexico to document the wintering population of Monarchs in the mountains of North Central Mexico. The animals wintering roosts were first discovered in 1975 in the states of Michoacan and Mexico.
Good population estimates were first attempted in 1993 when an index was devised to gauge their relative abundance by measuring the roosting area occupied by butterflies during the winter. This was made possible by the communal behavior of the Monarch to “pack” together in roost trees. Because of this “packing” behavior we can compare butterfly numbers on the wintering grounds from year to year by simply measuring the area occupied.
In the winter of 93-94 that area measured 6.23 hectares (15.39 acres). Butterfly numbers rose the next three years to an all time recorded high of 20.97 hectares (51.8 acres) in 96-97. But from that highpoint numbers have been in a decline until last winter the Monarchs occupied only 1.19 hectares (2.94 acres). That probably represents less than 100 million individual animals, a decline of almost 59% from the area occupied just one year ago.
Dr. Chip Taylor, Director of Monarch Watch, and a prominent Midwest butterfly researcher, cites several important factors to explain the Monarch butterflies precipitous decline:
1) The loss of milkweeds in row crops (corn and soybeans) due to the adoption of seed varieties genetically modified to tolerate treatment with herbicides. The utilization of these herbicide tolerant crops has all but eliminated milkweeds from these fields.
2) The push for the production of biofuels, which has resulted in the planting of 25.5 million more acres of corn and soybeans than were planted as recently as 2006. This increase has been at the expense of milkweed-containing Conservation Reserve Program land, grassland, and rangeland (as well as other crops).
3) Development, which consumes 6000 acres a day or 2.2 million acres a year.
4) Intensive farming that reduces the area from the edge of the road to the field, and management of our roadsides with the use of herbicides (and excessive mowing) which also eliminates milkweeds.
5) Deforestation of the oyamel fir forests – although this has declined over the last few years, the condition of these forests is less than optimal for the survival of overwintering Monarchs.
6) Unusual weather – and we had plenty of that during the 2012 Monarch breeding season. March was the warmest recorded since nationwide record keeping began in 1895. Warm weather tends allow returning Monarchs to spread north rapidly and arrivals of Monarchs in areas north of Oklahoma in April are often followed by low temperatures that delay development of the population. In 2012, first generation Monarchs moving north-northeast out of Texas arrived much earlier in the northern breeding areas than previously recorded. Historically, low overwintering numbers have followed the early arrival of Monarchs. These early establishments were followed by one of the hottest and driest summers in recent decades. Hot and dry conditions probably have the effect of reducing adult lifespan and therefore the number of eggs laid per female over its lifetime.
Some of these ominous trends are not likely to be reversed. One can only conclude that the survival of this beautiful animal is in peril.