Adult monarchs eat nectar. Do monarchs travel when and where their needs for food can be met? By monitoring the availability of nectar-producing flowers during spring migration, we can study how closely the two events are ecologically matched.

What is nectar?

Nectar is a sweet liquid secreted by plants, and especially by flowers. Nectars range in sweetness from as little as 8% to as high as 50%. The concentration of sugar in Coca-cola is only 10%, for comparison. Although nectar is known for its sweetness, it also includes additional compounds such as vitamins, oils, amino acids and others. Nectar is produced in the plant by glands called nectaries. Floral nectaries can be located on various parts of the flower, depending on the species.

Why do flowers produce nectar?

Flowers produce nectar as a reward for pollination, the process of transferring pollen from flower to flower. Many flowers need pollen to reproduce. However, because plants are immobile they need help with pollen transfer. An animal that transfers pollen from flower to flower is called a pollinator. By rewarding pollinators with nectar, the animals inadvertently help the plant with pollen transfer. This monarch, covered with sticky grains of pollen, is serving as a pollinator.

How is nectar connected to migration?

Monarch butterflies need floral nectar in the springtime to fuel migration and reproduction. The rate at which spring-blooming flowers develop is largely temperature-dependent; flowers bloom earlier in a spring with warmer temperatures. Because adult monarchs are generalists, they are able to eat nectar from a wide variety of spring flowers. This fact gives them some flexibility. In contrast, monarch larvae are specialists; they can only eat milkweed. The need for milkweed may determine when and where monarchs travel because even though adult butterflies don't depend on milkweed, their offspring do.

When do flowers produce nectar?

Each species of flower has its own phenology (timing of life cycle events). The amount of nectar in a flower depends on the species.

Even within a species, the quality and quantity of nectar can vary according to the age of the flower, the length of its season, the amount of precipitation, the ambient temperatures, and even the time of day. For example, in a study of dandelions in Alberta, researchers discovered:

• Larger flowers produced more nectar.
• The quantity and concentration of nectar were significantly higher in flowers 2 days old than in those 1 day old.
• Most flowers opened in the morning and closed in the afternoon, so nectar was not available for the full day.
• Nectar-sugar concentration and sugar value increased with increasing temperature.
• High nectar-foraging activity by honeybees coincided with peak nectar-sugar production.

Observe and Report

Help explore the connection between nectar and migration by sharing your observations. Monitor monarch habitat and report details about plant phenology (date of first flowers, type of flowers available) and visiting pollinators.