Seasonal temperature changes are an important factor in determining when plants come into bloom. If there are significant changes in annual temperature cycles over time, the blooming schedule can be altered worldwide. This begs an important question for plant pollination. Have the insects and other animals that service animal-pollinated plants altered their behavioral calendar in a similar way?

Using historical museum datasets and recent bee-monitoring data, North American researchers have examined this question in ten species of wild bees: Colletes inaequalis, Andrena crataegi, Andrena carlini, Andrena miserabilis, Osmia pumila, Osmia bucephala, Osmia atriventris, Osmia lignaria, Bombus impatiens, and Bombus bimaculatus. Over the past 130 years, there has been a significant shift toward emergence earlier in the Spring among these bees, which average approximately ten days earlier now than in the late 1800s. This trend was most pronounced in the last forty years.(Bartomeus et al, 2011)

Does this shift resemble a shift in the bloom schedule of the plants these bees visit? Changes in plant bloom times in response to climate change have been a subject of intensive study recently and data is available through several studies of native plants in North America, from herbarium records and monitoring programs (Miller-Rushing et al, 2006; Primack et al, 2004; Bradley et al, 1999; Cook et al, 2008). Among 106 native plants that are visited by these ten bee species, there is also a significant trend toward earlier flowering. This trend also became more pronounced in the last forty years.(Bartomeus et al, 2011)

Do these two shifts mean that bees will continue to be active during appropriate periods to take advantage of the bloom calendar? That is difficult to say. Emergence and bloom dates are quite variable, and all ten of these bee species visit many different species of plant, which have different bloom calendars. Another important research question: do schedule shifts also correspond for specialist plant-pollinator pairs, where a single species of animal visits a single species of plant?