Pollinators of the San Juan Islands

The pollinator network of the Haro archipelago is distinct from that found on the mainland. Geography and climate limit the dispersal of pollinators and the kinds of habitats available to them for feeding and nesting.

Preliminary studies of the San Juan and Gulf Islands and lower Vancouver Island (the Victoria Capitol Region) since 2010 suggest that while about 80 percent of the pollinator species recorded in the Salish Sea lowlands of Washington State and British Columbia are also seen in the archipelago as a whole, there are far fewer species on the smaller more isolated islands. Small islands offer limited floral resources and nesting area. Most insects can fly, moreover, but few are adapted to flying long distances without a break. One exception is the ability of bumblebees (Bombus) to fly “bee lines” between islands. As a result, bumblebees form a larger proportion of pollinator networks on smaller islands. The Salish Sea as a whole has relatively cold, windy springs cool, dry summers that can be challenging for insects that rely on sunshine and air temperature to warm their muscles for flight. Some bees can “shiver” to warm their muscles up internally, like the way that people wave their arms or jump up and down to generate muscle heat. And insects vary in how much heat they need to start, and how hot they can get in full-speed flight before they need to rest and cool down. Hover-flies, which become active at about 7°C , and bumblebees, which can fly at about 7-10°C, are advantaged by cool weather. Similarly, the drenching winter storms of the Pacific Northwest challenge the ability of solitary bees to keep their nests waterproof.




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Bombus mixtus, Blind Island

The length of the growing season is a related factor in the geography of pollinator species. The shorter the growing season, the less time bees have to collect pollen for their offspring. Nests may be smaller, with fewer eggs and less stored provisions in each egg chamber. While Syrphid flies do not make or provision nests, over-wintering in leaf litter or ponds as pupae (or sometimes as adults,) they produce multiple summer broods, so a short summer means one or perhaps two generations rather than the three or four that are possible in regions with longer growing seasons. Summers throughout the Salish Sea are relatively short due to latitude and the influence of the Pacific Ocean on climate. But the Haro archipelago falls within the “rain shadow” of coastal mountains, so its summers are uncommonly dry as well: a cool seasonal desert with annual precipitation as low as 36 cm. Plants respond by leafing out early and flowering before July: another challenge for pollinators.