Hummingbirds at Home: the effects of climate change on feeding behavior

Planning a vacation to an exotic location several time zones away is usually cause for joy and excitement, but what if you arrived at the airport only to discover your flight departed the day before and no one told you? What if your road trip to your favorite mountain lake was marred by a lack of signs to tell you where the gas stations are?  These challenges are similar to what hummingbirds may be confronting as they deal with the impacts of global climate change. Hummingbirds may be without the information they need to find their important nectar sources after migrating to their breeding areas.

Charts showing historic changes in temperature, sea level, and snow cover. IPCC, 2007
Source: Intergovernmental Panel on Climate Change (IPCC) (2007) IPCC Fourth Assessment Report: Climate Change 2007.
Fig 1.  Historic changes in temperature, sea level, and snow cover. Source: Intergovernmental Panel on Climate Change (IPCC) (2007) IPCC Fourth Assessment Report: Climate Change 2007.
A growing body of research (McKinney, et al. 2012) indicates flowers are blooming earlier because of warming temperatures.  There is potential for this change to impact the established synchronous relationship between hummingbirds arriving on their breeding grounds and bloom times of their food sources.  The degree to which hummingbirds are able to adapt to accommodate these changes is poorly understood and a comprehensive feeding behavior survey of hummingbird species across the country has yet to be undertaken.

Audubon's Hummingbirds at Home program was designed to mobilize citizen scientists across the US to bolster current research by documenting the feeding patterns of hummingbirds.

Figure 1 shows the historic trends in surface temperature, sea level, and snow cover that  document evidence of climate change.  These higher temperatures are driving sea-level rise and changes in snowpack which in turn are reshaping when and where the nectar resources hummingbirds rely on are available.   

Hummingbirds rely on nectar for up to 90% of their diet and rely heavily on the timing of nectar blooms during their breeding season.    The breeding distribution of Broad-tailed Hummingbirds, for example, corresponds very closely with the start of the growing season in the western U.S. Birds tend to breed in areas that start greening up in mid- to late May (Map 1). The importance of timing for migrating Broad-tailed Hummingbirds is also evident when you look more closely at availability of the flowers they depend upon for nectar, such as the Glacier Lily. 

Map showing breeding distribution of Broad-tailed Hummingbird and growing season.
Left map: National Audubon Society, Right map: Courtesy of the U.S. Geological Survey, http://phenology.cr.usgs.gov/get_data_1km.php
Map 1. Breeding distribution of Broad-tailed Hummingbird (left) coincides with the start of the growing season (right) in that landscape.  Source: Left map: National Audubon Society, Right map: Courtesy of the U.S. Geological Survey,  http://phenology.cr.usgs.gov/get_data_1km.php
If the timing of blooms of these plants were to change, what kind of impact would this have on the Broad-tailed Hummingbird? Will the Broad-tailed Hummingbird be able to find new sources of nectar during this important part of its lifecycle? Is this also happening to other hummingbird species?   The timing of arrival of at least one hummingbird species, the Ruby-throated Hummingbird, onto their breeding grounds, is changing (Courter, et al. 2013). Will these changes affect local pollination systems and will the Ruby-throated Hummingbird be able to keep pace with the accelerated warming?

These are the types of questions Audubon hopes to gain insight into through data collected with Hummingbirds at Home. The program was developed to help us learn where these important nectar rich flowers are and how climate change is affecting when they bloom. Citizen scientists in this project document hummingbird feeding behavior across the country by recording the timing of nectar plant blooms locally, what hummingbirds are feeding on, and when feeding occurs as they arrive on their breeding grounds and throughout the breeding season.   Are hummingbird feeders and/or non-native plants supporting hummingbirds at a level that native plants do not because of the change in bloom times?  Where and when might hummingbirds be most vulnerable due to a scarcity of nectar resources? These are some of the question that guided the design of this program.

As the data collected shows Audubon scientists what the hummingbirds are feeding on, we can determine  if these birds are changing their feeding behavior.  Focused on the relationship between hummingbirds and their feeding sources, Hummingbirds at Home differs from other bird monitoring programs in that participants do not record the numbers of birds seen, but record the species, nectar sources, and feeding behavior seen.  

Spring of 2013 is the first year of the program and it will take a few years of data collection before patterns begin to emerge. We will look to the data to determine if recommendations should be made encouraging participants to plant certain flowering plants in their survey locations and then to follow up with additional surveys to measure the impacts.  In the case of bloom timing mismatches, we hope eventually to learn if alternate nectar sources, like feeders, make a difference in hummingbird breeding success and survival.      

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Want to help hummingbirds? Hummingbirds at Home  welcomes your participation to report the hummingbirds in your yards!  The project joins Audubon's Christmas Bird Count and the Great Backyard Bird Count as part of Audubon's year-round citizen science programs.  

Find out more at www.hummingbirdsathome.org

References:

Jason R. Courter, Ron J. Johnson, William C. Bridges, and Kenneth G. Hubbard. Assessing Migration of Ruby-Throated Hummingbirds (Archilochus colubris) at Broad Spatial and Temporal Scales. The Auk 2013 130 (1), 107-117 http://www.bioone.org/doi/abs/10.1525/auk.2012.12058

Amy M. McKinney, Paul J. CaraDonna, David W. Inouye, Billy Barr, C. David Bertelsen, and Nickolas M. Waser 2012. Asynchronous changes in phenology of migrating Broad-tailed Hummingbirds and their early-season nectar resources. Ecology 93:1987-1993. http://dx.doi.org/10.1890/12-0255.1, http://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=124345&preview=false