Wednesday, June 19, 2013

By Matt Pelikan
Published: July 2, 2009

As I sit down to finish this column on the penultimate day of June, it is - surprise! - overcast, cool, and drizzling outside. As June 2009 vies for the dubious title of the least sunny June on record in eastern Massachusetts, consequences ripple across the Vineyard.

In the human domain, many effects are economic. The gloom has surely done the tourism industry no good. And last week, this paper reported the near-total loss of the early-season hay crop - not through lack of growth, which has been vigorous, but through lack of weather suitable for cutting and drying hay. Closer to home, half the beans I planted rotted in the ground, and many of my vegetable transplants, insufficiently hardened off, were surprised and badly sunburned by one of the few sunny days we did have.

Wild Side has also been pondering the effects of a dismal June on Island wildlife. The picture is a complicated one; such unusual weather undoubtedly causes strong and potentially far-reaching effects, but generalizations are elusive. Particular species gain or lose depending on their requirements and the nature of their interactions with other species.

Birds as a group tend to be vulnerable to sustained bad weather during their breeding season. Rain poses the threat of hypothermia to unfeathered nestlings, and, by suppressing insect activity, cool, wet days complicate the task of adult birds foraging for insects to feed their young. Smaller bird species, which tend to lose body heat faster than larger ones, are at particular risk, as are species that rely heavily on insects. Swallows and chimney swifts, for example, may face a near-washout this nesting season; aerial insectivores with an energy-intensive lifestyle, they can lose all their young to a few consecutive days of rain in June. Historically, rainy Junes have caused periodic population crashes among swallows that have taken many years for the birds to fully recover from.

Some larger species fare better. Common grackles, for example, appear to have launched a bumper crop of squawking fledglings this season (this species is already beginning to aggregate into large, post-breeding flocks). Aggressive predators with diverse tastes in prey, grackles have had no problem keeping their young well fueled. Perhaps surprisingly, chickadees, one of our smaller nesting birds, also appear to have fared well (the pair in our yard recently fledged four vigorous youngsters). But chickadees nest in holes and cavities, which shelter their young from inclemency, and the adults are notoriously versatile and intelligent foragers, well suited to respond to difficult conditions. For birds that have strategies to deal with bad weather, the hard times their competitors face will simply prove to be one more advantage.

In terms of plant life, the cool, damp weather has prompted vigorous growth among species equipped to take advantage of it. Lawns and hay fields have exemplified this, as most of the species used for these purposes thrive in cool, wet conditions. But much of the Vineyard's native flora, adapted to heat and drought instead, languishes from insufficient sun and derives no benefit from extra water. Our various milkweed species offer good examples: while local variation is certainly evident, overall these plants are suffering through a season of limited vegetative growth and delayed flowering.

Insects, too, are likely to find their development delayed, and their reproduction inhibited, by dreary weather. Dependent on sunlight and the ambient temperature to regulate their body temperatures, many insects have surely fed less actively and mated less successfully than in a typical year. On the other hand, their reduced activity may have made these insects less visible to predators, enhancing survival. And lush, fresh growth resulting from rain translates into more digestible, nutritious food for insects, at least species that feed on plants that have benefited from the rain. The net effect may be beneficial for many insects: a delayed season, but high survival and vigorous health.

Assuming summer weather finally kicks in, what then? Very likely a lot of frantic catching up by plants and insects that have had their life cycles delayed. The result may be a sudden burst of flowering, and of emergence of adult insects. This phenomenon, too, will have complex effects. Predators and parasites will be overwhelmed by this sudden wealth of resources, and overall mortality of prey species may be lower than normal as a result. While it may not be evident to the casual observer, it seems likely that some dramatic changes in population will be evident among insects, and these changes may persist over several more seasons before a normal balance is restored.

Upcoming months, then, should be entertaining for observers of natural history. There will surely be consequences from this dismal June. But beyond that, about all that can safely be said is that those consequences will be far-reaching, unpredictable, and sometimes surprising.