Evaluating the effects of observation period, floral density, and weather conditions on the consistency and accuracy of timed pollinator counts

Abstract

Insect pollinators are experiencing substantial declines as a result of habitat loss, agricultural intensification, invasive pests, and climate change. To investigate factors causing pollinator declines, evaluate the success of conservation measures, and institute long-term monitoring schemes, it is essential to validate and standardize pollinator sampling techniques. This study investigated how sampling duration, weather conditions, and abundance of floral resources influenced the results of timed pollinator counts by repeatedly sampling the same pollinator assemblage in an Irish meadow. The likelihood of detection of Apis mellifera, Bombus spp, solitary bees, and Syrphidae was strongly associated with the density of floral units or floral cover in the observation plot. Also, even though protocol criteria restricted pollinator counts to the middle of the day and benevolent weather, pollinator counts were strongly influenced by factors such as cloud cover, light levels, wind speed and relative humidity. Increasing the duration of the timed counts from 5-minutes to 30-minutes considerably increased the probability of detection of each pollinator group. Additionally, the perceived diversity of the pollinator assemblage at the meadow was markedly affected by sampling duration and floral abundance. To improve the consistency or comparability of studies using timed pollinator counts, we recommend that criteria are set restricting surveys to narrow ranges of weather conditions and floral density when possible. Additionally, pollinator field investigations or monitoring programs would benefit from a systematic evaluation of how erroneous non-detection of target taxa can be reduced to acceptable levels by modifying sampling duration.

Responses in honeybee and bumblebee activity to changes in weather conditions

“…This variability makes Ireland an ideal location for assessing the effects of weather on bees, and, as Irish weather is distinct from the rest of Europe, a study here could provide valuable insights as to how pollinator behaviour may change under different climate change scenarios (Sanderson et al 2015 ). Although the effects of weather on honeybee and bumblebee activity have been previously explored (Corbet et al 1993 ; Tuell and Isaacs 2010 ; Lee et al 2016 ), simultaneous observations of the two species at the colony are scant; at the time of writing, the only study on the effect of weather on pollinator activity in Ireland was made by Mahon and Hodge ( 2022 ), although this was performed at flowers, not the colony, and only within a narrow, pre-determined range of weather conditions.…”

Glacier retreat decreases plant-pollinator network robustness over space-time

“…To standardise observations over time, we walked transects at a slow and steady pace for 15 minutes per orthogonal line, for a total of 30 minutes per transect (Martínez-Núñez et al 2022 ). Sampling sessions were carried out on sunny and low-windy days from 8:30 a.m. to 5:30 p.m. (Fijen et al 2018 , Martínez-Núñez et al 2022 , Mahon and Hodge 2022 ). We sampled each site eight times, for a total of n =128 temporal replicates.…”