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Hummingbirds, lilies thrown off by climate change

Broad-tailed hummingbirds' relationship with glacier lilies is being threatened by climate change. (Bill Ratcliff/National Park Service)

The implications of climate change can reverberate through ecosystems, wreaking havoc on the delicate interactions that have evolved between species over millions of years.

In western North America, the relationship between the glacier lily and the broad-tailed hummingbird is in danger. The plant flowers in early spring, when the first hummingbirds arrive. Or at least it used to. A new study by AAAS member David Inouye and Amy McKinney of the University of Maryland and colleagues shows the lily's first blooms are appearing two to three weeks earlier than they did forty years ago. The timing of these first blooms is no longer synchronized with the arrival of the hummingbirds, who depend on the lilies for nectar.

AAASMC recently talked to Inouye about what this means for broad-tailed hummingbirds, glacier lilies, and other species threatened by our changing climate.

AAASMC: Can you explain the relationship between glacier lilies and broad-tailed hummingbird? Why is timing (of blooming and migration) especially important?
Professor David Inouye, University of Maryland
: Glacier lilies are the second species to bloom after the snow melts at our study sites, and the Broad-tailed Hummingbirds visit them for nectar when they arrive from their winter grounds in Central America. Changes in the phenology (seasonal timing) of migration and of flowering are one of the best ways to measure the ecological consequences of the changing climate. Given the scarcity of other floral resources early in the season, the glacier lily (and then larkspur) is an important component of the hummingbirds' diet.

AAASMC: You and your colleagues found that the time between the first hummingbird and the first bloom has collapsed by 13 days over the past 40 years. Is this a dramatic change? How could this affect the hummingbirds?
: Yes, 13 days is a significant portion of the flowering period for most of the high-altitude wildflowers, so that is a dramatic change. If this trend continues, the hummingbirds will arrive at their summer breeding grounds after one of the important nectar resources they now utilize is already finished flowering. In addition to this, Broad-tailed Hummingbird reproduction is synchronized closely with peak floral abundance of the later important nectar resource: larkspur (Delphinium nuttallianum). As stated above, if hummingbirds continue to arrive later into the flowering season, the timing of their reproduction may be mistimed (i.e., later) with peak floral abundance of the larkspur, resulting in fewer offspring.

AAASMC: In the paper, you say that the asynchrony between lilies and hummingbirds is more problematic in more northern climates. Why is that?
: Higher latitudes and higher altitudes are experiencing stronger and more rapid consequences of climate change than other areas, especially at lower latitudes and elevations. Our study site at 9,500 feet in the Colorado Rocky Mountains does seem to be characteristic of that pattern. These hummingbirds began their migration from Central America based on lower-latitude seasonal cues. Because the effects of climate change are occurring at a faster rate at higher latitudes compared to lower latitudes, hummingbirds do not appear to have much of a problem with the timing of food resources along the lower-latitude portions of their migration route, but arrive later at northern breeding grounds, after important early season flowers have already started to bloom. In this case, arriving later in Colorado may have strong consequences.

AAASMC: Do you think the hummingbirds will be able to adapt to this consequence of climate change?
: It's possible that hummingbirds could learn to change the timing of their migration, and that they could learn to use additional floral resources. But as the growing season is getting longer, it seems that a mid-summer period of low floral resources is developing, which will also challenge the ability of hummingbirds at this high-altitude site to reproduce.

AAASMC: Could a disruption to the hummingbird-glacier lily relationship have more far-reaching implications in the ecosystem?
: The hummingbirds are important pollinators of several species of flowers that are not usually visited by other pollinators, so for those species, and for the animals that depend on them as herbivores or seed predators, there would be significant consequences if the hummingbirds decline in abundance.

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Representative Image Caption
Broad-tailed hummingbirds' relationship with glacier lilies is being threatened by climate change. (Bill Ratcliff/National Park Service)
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