Nectar flow is when one or more major nectar sources are blooming and producing nectar. An important factor in the plants ability to secrete nectar is the weather, in particular the ambient weather conditions. Plants have an optimum range of temperature for nectar production, determined by their habitat and species characteristics. For example, cold night temperatures in spring affect the nectar production. But also later in summer with aridity and high temperatures (esp in places like the Mediterranean) plants stop secreting nectar. The bees are happy to fly, but there is no nectar to forage for.
When nectar is available, bees (and other pollinators) will collect it for the colony . It is usually easy to detect pollen being carried into a hive, as bees place it in their pollen baskets. Nectar however, is impossible to spot since it is carried into the hive via the stomachs of foraging bees.
How do you know there is a nectar flow?
Increases in hive weight indicate that the bees are collecting nectar and making honey. This is not a straight line on your weight graphs as you will see below.
The above graph shows you this weight increase (pink line), the peak flight noise (green line), and mean fanning (black line). The overall weight goes up – but you see the daily variances. During the day the weight increases, and you see the flight noise peaking. At night, when the bees do a lot of night time fanning to evaporate the water in the nectar, the weight drops. The fact that the overall weight of the hive increases, means that there is a nectar flow on.
The opposite of nectar flow is when there is no nectar available for bees to forage on. In the United Kingdom, there is a well known ‘June Gap’ with a sudden reduction in the availability of pollen and nectar. This is a period just after Spring flowering in May and before Summer flowering in July and August where not many plants flower.
A good example can be seen in the following graph ;
This graph shows warm June weather with good daytime temperatures (green line), no rainfall (as shown by flat red line) and the bees out flying (yellow line). However hive weight is static/slight decline (blue line).
These hives were located is an area of arable farmland in the UK with a predominance of Oil Seed Rape (OSR). Once the OSR had finished flowering in May there is no local forage for the bees. This shows the effect of intensive monoculture with very little natural wild flower or trees. In the UK this is referred to as the June Gap. In these sort of landscapes beekeepers sometimes have to feed bees in June or move them.
Based on anecdotal evidence it appears that the June Gap does not occur in all areas of the UK or even every year but it is common enough to be established in beekeeping folklore. The weather will affect the times when plants flower and can make the gap greater or smaller. Also, some plants will be in flower – just less of them.
Climate Change and Nectar Flow
Nectar flow can be seen as an indicator of environmental changes over time. As we know, scientific research produced climate change models which predict an increase in temperature for the end of the 21st century. This reduces the nectar secretion in plants and therefore significantly reduces available resources for both wild bees and honeybees.