Flowers of a given species all produce nectar at about the same time each day, as this increases the chances of cross-pollination. The trick works because pollinators, which in most cases means the honeybee, concentrate foraging on a particular species into a narrow time-window. In effect the honeybee has a daily diary that can include as many as nine appointments — say, 10:00 a.m., lilac; 11:30 a.m., peonies; and so on. The bees’ time-keeping is accurate to about 20 minutes.
Honey bee nectaring on button willow (from NY Times article cited below)
The bee can do this because, like the plants and just about every living creature, it has a circadian clock that is reset daily to run in time with the solar cycle. The bee can effectively consult this clock and “check” off the given time and associate this with a particular event.
Honeybees really are nature’s little treasures. They are a centimeter or so long, their brains are tiny, and a small set of simple rules can explain the sophisticated social behavior that produces the coordinated activity of a hive. They live by sets of instructions that are familiar to computer programmers as subroutines – do this until the stop code, then into the next subroutine, and so on.
These humble little bees have an innate ability to work out the location of a food source from its position in relation to the sun. They do this even on cloudy days by reading the pattern of the polarization of the light, and pass this information to other bees. In the dark of the hive, they transpose the location of a food source in the horizontal plane through the famous “waggle” dance into communication in the vertical plane of the hive.
Honeybees can tell their sisters how far away the food is up to a distance of about 15 kilometers. For good measure, they can also allow for the fact that the sun moves relative to the hive by about 15 degrees an hour and correct for this when they pass on the information. In other words, they have their own built-in global positioning system and a language that enables them to refer to objects and events that are distant in space or time.
German scientists in the early part of the last century called this ability of bees to learn the time of day when flowers start secreting nectar and visit the flowers at appropriate times Zeitgedächtnis, or time-sense. But the species of flowers in bloom, say, this week, is likely to be replaced by a different species at a different location next week or the week after. The bee needs a flexible, dynamic appointments system that it continually updates, and it has evolved an impressive ability to learn colors, odors, shapes and routes, within a time frame, quickly and accurately.