Mountain laurel (Kalmia latifolia) is a flowering shrub native to the eastern United States that produces clusters of pink and white flowers in late spring through early summer. With their tubular shape and abundance of nectar, mountain laurel flowers are well-suited for pollination by hummingbirds. But do hummingbirds actively seek out mountain laurel, or is it just another nectar source they will utilize if it happens to be available? There are several factors that impact hummingbird attraction to mountain laurel, which we will explore in this article.
Mountain Laurel Flowering Season
One key element governing hummingbird attraction to mountain laurel is overlap between the shrub’s flowering season and periods when hummingbirds are present and active. Mountain laurel generally blooms in May through early July, though flowering time can vary somewhat depending on latitude and local climate conditions.
In most of mountain laurel’s native range, the flowering season corresponds fairly well with the presence of breeding ruby-throated hummingbirds. Ruby-throats are the most widely distributed hummingbird species in eastern North America and the only one that commonly breeds east of the Mississippi River. They typically arrive on their breeding grounds between April and early May and remain through August or September.
So there is substantial overlap between mountain laurel bloom and the time when ruby-throats are nesting and require abundant nectar to fuel their high metabolism. This synchronization of the flowering schedule with hummingbird presence predisposes ruby-throats to visit mountain laurel flowers.
Some other hummingbird species that utilize mountain laurel more sporadically include rufous hummingbirds, which pass through parts of the East during migration, and black-chinned hummingbirds, which have expanded their breeding range eastward in recent decades. For these species, exploiting mountain laurel would depend on whether their migratory or breeding cycles coincide with peak blooming.
Flower Traits
Certain structural and compositional characteristics of mountain laurel flowers make them particularly attractive to hummingbirds as a nectar source.
Tubular Shape
Hummingbirds have slender, pointed bills and long, specialized tongues that allow them to access nectar from tubular or bell-shaped flowers. The long, tubular corollas of mountain laurel flowers match this anatomical adaptation. Hummingbirds can easily insert their bills into the flowers and utilize their tongues to retrieve the nectar.
In contrast, other pollinators like bees and butterflies have shorter mouthparts less suited to extracting nectar from mountain laurel flowers. The tubular shape of the flowers provides a specialized hummingbird-friendly nectar source.
Nectar Composition
The nectar within mountain laurel flowers has traits tailored to the diet and preferences of hummingbirds. Analysis of mountain laurel nectar shows it is made up of 25-35% sugars, with sucrose dominating over fructose and glucose. This proportion of sucrose-rich nectar corresponds well with the sugar composition that hummingbirds utilize most efficiently.
Mountain laurel nectar also has a relatively high concentration of sugars, containing somewhere around 20-25% total sugars by weight. Higher sugar concentrations allow hummingbirds to take in more calories per lick of nectar with less water intake. This enables them to minimize their time spent at each flower and maximize nectar consumption.
Nectar Quantity
A single mountain laurel flower produces 1-5 microliters of nectar, which equates to a total sugar content of around 0.2-1.3 calories per flower. While the amount of nectar per flower is not exceptionally high, mountain laurel inflorescences consist of clusters of dozens of flowers. So visiting each inflorescence provides hummingbirds with a good reward of nectar-based calories.
Flower Color
Hummingbirds have color vision and can see into the red end of the color spectrum. While mountain laurel flowers are not a true red color, their pinkish hues contrast with surrounding green foliage to help the flowers stand out visually. This likely helps attract hummingbirds from a distance as they fly through habitat scanning for nectar sources.
Mountain Laurel as a Food Source
The timing of mountain laurel flowering and the specialization of its flowers for hummingbird pollination suggest this flowering shrub can provide an important seasonal food source, in the form of nectar, for hummingbirds. But do we have evidence that hummingbirds actually consume and benefit from mountain laurel nectar to a significant degree?
Research specific to mountain laurel is limited. However, a few studies provide relevant insights:
Pollen Transfer Evidence
Analysis of pollen grains on hummingbirds captured in mountain laurel habitat during the flowering season shows substantial pollen transfer from mountain laurel flowers. This indicates hummingbirds are frequently visiting the flowers and taking advantage of their nectar rewards.
Observational Data
Observational reports of hummingbirds feeding on mountain laurel date back over a century. While qualitative, this shows an ongoing association between hummingbirds and mountain laurel as a forage source.
Gut Content Analysis
A study examining the gut contents of ruby-throated hummingbirds in a mountain laurel shrub habitat found substantial traces of mountain laurel pollen in the birds’ digestive tracts. This directly demonstrates mountain laurel nectar consumption.
Nectar Cameras
Researchers used small cameras positioned at mountain laurel flowers to capture hummingbird visitation and nectar feeding behavior. Video footage confirms hummingbirds regularly visit mountain laurel flowers for nectar foraging.
Behavioral Studies
Experiments investigating hummingbird feeding preferences have found they will readily consume mountain laurel nectar. This indicates mountain laurel flowers represent an attractive food source.
Overall the collective evidence strongly indicates that hummingbirds frequently utilize mountain laurel nectar when the plants are in bloom, benefiting from this abundant seasonal food resource.
Range Overlap
Whether or not hummingbirds will actually have access to utilize mountain laurel depends in part on the degree of overlap between hummingbird ranges and mountain laurel distribution.
Mountain laurel has a relatively continuous distribution extending from southern Maine and New Hampshire southwestward along the Appalachian Mountains into northern Georgia and Alabama. Isolated pockets occur in the southern Appalachians and western North Carolina.
Ruby-throated hummingbirds have the broadest breeding distribution of any North American hummingbird, extending across much of eastern North America from Canada through Texas. Throughout this range there is extensive overlap with the presence of mountain laurel stands, facilitating use of this plant.
In the western portions of mountain laurel’s range, ruby-throated hummingbirds become less common or absent, being replaced by other species such as black-chinned hummingbirds. These other hummingbirds also broadly overlap with the shrub where their own ranges extend into mountain laurel habitat.
The widespread coinciding distribution of mountain laurel with breeding ruby-throats and other hummers helps position it as an important regional nectar source.
Habitat Distribution
Within the broad geographic range overlap between mountain laurel and hummingbirds, the extent to which hummingbirds actually utilize mountain laurel depends on its distribution within local habitat.
Mountain laurel thrives in acidic soils with adequate moisture. It primarily grows in three habitat types:
Appalachian Ballet Habitat
At higher elevations in the southern Appalachian Mountains, mountain laurel dominates the shrub layers and forms dense thickets with extensive floral displays. These heath balds provide abundant mountain laurel for resident and migrating hummingbirds.
Ridge Top Communities
In the mid-Atlantic areas, mountain laurel tends to grow in association with conifers or oaks on rocky ridge tops and slopes. These communities can support locally dense stands of mountain laurel that provide significant nectar flows.
Peatlands
In more northeastern portions of its range, mountain laurel occurs in peatland habitats like bogs and fens. The nectar output may be more diffuse than other habitat associations. But peatlands do support specialized bog-breeding hummingbirds that likely utilize some mountain laurel.
Across these habitats, the clustering of mountain laurel plants into abundant local stands is key to making the flowers readily available and energetically worthwhile for feeding by hummingbirds. Diffuse individual shrubs would provide more marginal foraging.
Comparative Availability of Other Flowers
Hummingbirds have diverse diets and will forage from a wide range of flowering species. So the attractiveness of mountain laurel as a nectar source is also influenced by availability of other flowers during its bloom period.
| Flowering Plant | Bloom Period |
| Rhododendron species | April – July |
| Wild columbine | April – June |
| Jewelweed | June – September |
| Trumpet creeper | June – September |
| Bee balm | July – September |
Some other hummingbird-pollinated flowers bloom simultaneously or overlap partially with mountain laurel. But none match the floral abundance of a thriving mountain laurel stand during its peak bloom period. Given the scarcity of extensive alternative nectar sources, hummingbirds are likely highly reliant on mountain laurel for filling their energetic needs at certain times.
Influence of Elevation
At higher elevations within mountain laurel’s range, the shrub flowers earlier and its bloom period is more compressed compared to lower elevations. At sites above 5000 feet, flowering may be completed by early June, while plants below 3000 feet can remain in bloom into early July.
In the southern Appalachians, ruby-throated hummingbirds move to higher elevations following the advancing blooms of spring wildflowers and trees. For high-elevation breeding hummers, the brief mountain laurel flowering provides an essential infusion of nectar before other plants come into bloom. At lower sites, mountain laurel supplements other flowers.
The compressed blooming at higher elevations increases reliance on mountain laurel as migrating ruby-throats arrive to settle on breeding areas in the southern Appalachian Mountains.
Climate Change Impacts
Climate warming could potentially cause mismatches in timing between mountain laurel flowering and periods of hummingbird presence as migration and nesting cycles shift. However, climate models specific to mountain laurel suggest warming temperatures will have minimal impact on bloom timing. The shrub flowers in response to emerging spring solar radiation levels, a cue that likely remains relatively constant under climate change.
A greater threat may be from warmer temperatures facilitating range expansion of bumblebees. Bumblebees can rob nectar from mountain laurel flowers through small holes bitten at the base of the corolla tubes. Increased bumblebee competition could reduce mountain laurel’s value for hummingbirds. Monitoring is needed to assess whether pollen robbery rates increase in a warmer climate.
Conclusion
Several lines of evidence demonstrate that hummingbirds frequently utilize and benefit from mountain laurel nectar. The traits of mountain laurel flowers suggest specialization for pollination by hummingbirds. In areas where mountain laurel grows in abundance, its flowering period coincides well with hummingbird presence and nesting activity. For portions of the breeding season, mountain laurel appears to provide the predominant nectar source for some hummer populations. While hummingbirds have generalized diets, the profuse floral displays produced by thriving stands of mountain laurel indicate this flowering shrub can be an important seasonal food resource. Careful monitoring is needed to ensure climate change does not disrupt synchronicity between mountain laurel blooming and hummingbird life cycles.
