Monitoring early season bee activity and the first nectar flow

With the arrival of spring the bees are increasingly active however the weather is still changeable and nectar flows can be short and intermittent. Monitoring hive weight, colony activity and weather during this important time provides valuable insight into colony status to help your bees get the best possible start to the season.

First Nectar Flow of the Year

Bee on Tree Heather

Bee on Tree Heather

There has been some fabulous weather at our apiary in Italy this spring. The nectar from tree heather (Erica arborea), dead nettles (Lamium purpureum) and fruit trees (pears, peaches) began to flow around the middle of March.

The weight graph from one of the hives (Figire 1 below) shows the nectar flow beginning on 19th March when the hive weight starts to increase. However the rise in weight is short lived as it starts to fall away again after only a few days.

Figure 1: Hive Weight

Figure 1: Hive Weight

Overlaying the cumulative rainfall readings taken from our integrated weather station shows there was a few days of rain around this time (March 23rd – March 26th). Rainfall can stop some flowers producing nectar for a day or two after the rain has stopped, so hive weight can continue to fall even when good weather returns as the bees consume stores.

 Figure 2: Hive Weight and Cumulative Rainfall

Figure 2: Hive Weight and Cumulative Rainfall

This can be seen on the graph above, with weight starting to increase again around 29th March, a few days after the rain stopped. This time cherry (Prunus avium) nectar is in abundance too.

Examining the hive weight graph more closely reveals fascinating insight into bee activity at the hive. With Arnia’s high precision hive scales you can see the weight of foragers leaving and returning to the hive.  This is shown by the daily fluctuation in hive weight.

 Figure 3: Weight showing foraging activity

Figure 3: Weight showing foraging activity

In the above graph, hive weight drops in the morning by around 300g as foragers leave the hive. This equates to about 3000 bees (an average bee weighs 0.1g). Weight increases again in the afternoon as bees return with nectar, and by the end of the day the hive is heavier than at the start of the day. Overnight there is a steady decrease in hive weight; this is the bees fanning to evaporate moisture to process the honey ready for capping. Also, if you look carefully you can see that in the middle of the day there is a time when many bees come back to the hive before going out again. We have noticed this before; we jokingly call it their lunch break! By adding temperature to the graph from the weather station it shows the temperature at which the bees start flying.

Figure 4: Hive weight and temperature in the sun

Figure 4: Hive weight and temperature in the sun

Monitoring acoustics adds to the richness of the data and the understanding of bee activity at the hive. The graph below shows the start of a nectar flow at a hive in the UK.  You can see intermittent hive weight increase from the end of March through early April.

Figure 5: Hive Weight

Figure 5: Hive Weight

Adding flight noise to the graph clearly shows forager activity. In the graph below you can see flight noise (red line) corresponding to the hive weight changes as foragers are collecting nectar.  However on some days flight noise is reduced and the hive shows no weight gain, or a slight weight loss. (e.g. 4th- 5th April)

Figure 6: Hive Weight and flight activity

Figure 6: Hive Weight and flight activity

Focusing in on that period and adding temperature in sun (blue line), temperature in shade (light green) and rainfall shows exactly what is happening (Figure 7 below). There is rainfall early morning of 4th April and the rest of the day is cool and cloudy with no sunshine. You can tell this as temperature in the sun and shade are the same. The bees are still flying, though activity is reduced (as shown in the graph above), and there is no weight increase. The weather gets warmer and sunnier on 5th April but nectar isn’t flowing again until 6th April, when hive weight starts to increase.

Figure 7: Hive weight and weather conditions

Figure 7: Hive weight and weather conditions

One final insight from the same colony is to map fanning noise with hive weight. This shows clearly the night time fanning activity of the bees to evaporate moisture and process honey. This corresponds to the overnight decrease in hive weight.

graph8 uk weigh and fanning

The graph shows a big increase in fanning activity (green line) in the evening following a day when nectar is brought back to the hive. However following days with no weight gain, fanning activity is reduced.

The example hive data presented shows the impact on bees of changeable weather and intermittent nectar flows during spring. It highlights the need for beekeepers to remain vigilant during this important early season period. The ability to overlay different sensor data to build a picture of what is happening at your hives provides valuable knowledge of colony strength and behaviour in the context of the prevailing weather.