14 September, 2022

Evaluating effects on pollinator counts

By Neil Mahon and Simon Hodge
Irish meadow with pollinators

Insect pollinators, including bumble bees, honey bees, and hoverflies, are experiencing substantial declines across the globe because of habitat loss, modern agricultural practices, invasive species, and climate change. To truly understand the cause of these declines, it is essential that pollinator sampling techniques, even those that are widely accepted, are validated and standardized. This study investigated how sampling duration, weather conditions, and the local abundance of flowers influenced the results of pollinator counts in an Irish meadow. Over 20 days, we recorded 876 foraging pollinators within 2m X 2m quadrats, which included 467 bumble bees, Bombus spp., 64 honey bees, Apis mellifera, 64 solitary bees, and 281 hoverflies, Syrphidae. We found that factors such as cloud cover, light intensity, wind speed, and humidity had strong influences on the number of foraging pollinators, while the number of bumble bees, solitary bees and hoverflies increased with both the density and cover of flowers. However, the number of flowering species, air pressure, and temperature had no notable effect on the count of any pollinator group. We also found that the probability of detecting a foraging pollinator was improved if the duration of the observation period was increased from 5-minutes to 30-minutes. Accordingly, the diversity of pollinators we perceived to be present in the meadow was also affected by the sampling duration. Overall, our results suggest that both the consistency and comparability of pollinator field studies could be improved by sampling in areas with a high density of flowers, and only when weather conditions are favourable. Additionally, pollinator monitoring programs would benefit from evaluating how erroneous non-detection of a species can be reduced to acceptable levels by modifying the sampling duration.

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