Hummingbird Monitoring Network

Research

Research is one of the most important aspects of conservation because it helps us better understand hummingbirds and the role that they play in their environment. By furthering our understanding of the birds, we are better able to protect them. Research at HMN is question driven. As scientists learn about HMN and propose new research for us to sponsor, our research will broaden in its scope. Currently, our active research is based on questions arising from our monitoring work.

Projects

Feeder/flower study at Tohono Chul Park
Question: How do nearby nectar resources affect hummingbird visitation rates to feeders?
Background: In order to estimate hummingbird populations and identify trends effectively, we need to understand how the distribution and abundance of nectar resources affects hummingbird abundance and distribution in a region. Our first project investigates the effect of flower abundance on feeder visitation at a garden park. As we expand our investigation to the landscape level, we need to both map the nectar resources in regions and then determine how to estimate the abundance of these floral resources.

» View Research Summary

Claret Cup Cactus

Botany Program
Question: How does the distribution of nectar resources affects hummingbird
abundance and in turn what factors are beneficial for maintaining these resources
Background: Thanks to a National Park Service grant, the Hummingbird Monitoring Network's botany research program began in May, 2004. An Arizona botanist, Meg Quinn, began mapping locations of plant species used as nectar resources by hummingbirds in the Chiricahua and Huachuca Mountains of southeastern Arizona. In 2005, she will continue mapping these resources and begin to quantify their abundance. To see some of the results of 2004 and learn more about the 2005 season, visit the botany section. Once we have mapped the nectar resources and are able to quantify them, then we will be able to ask large- scale questions such as how does fire history and management practices or other disturbances such as grazing affect the distribution of nectar resources.

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Pollination Ecology

Question: How important is this plant as a nectar resource for hummingbirds and to what extent do hummingbirds serve as pollinators for this plant.

Summary: Dr. Marilyn Loveless, Wooster College, OH, will head a study in collaboration with the Hummingbird Monitoring Network and the Southwestern Research Station to study the hummingbird/plant interaction of the desert shrub, Erythrina flabelliformis (Southwestern Coral Bean). The shrub can grow to 15 feet in height but is usually much shorter. It has bright red to reddish-orange tubular flowers about three inches long arranged in a terminal cluster. Flowers appear before the leaves in May and June usually on dry rocky hillsides at elevations between 3,000 and 5,000 feet. The plant is a member of the pea family (Leguminosae) and produces pods filled with bright red seeds that are very poisonous. We are interested in determining the importance of this plant species as a nectar resource for hummingbirds in the southwest during a period when other nectar resources can be scarce. We will also quantify the pollination service of hummingbirds to Erythrina as they distribute pollen among individual plants to minimize the negative effects of in-breeding. We hope to obtain authority to mark individual hummingbirds with tiny bits of colored thin foam-board in order to estimate how many birds of the four to five species of hummingbird use this nectar resource in the areas studied. Dr. Loveless will be employing at least one student to assist in the project that will take place during May and June 2007.

Anna's Hummingbird

Nesting Habitat Study
Question: What are the habitat requirements for successful nesting of breeding hummingbird species in the Madrean Pine-Oak Woodlands and does grazing affect these requirements
Background: Another question arising from our monitoring work deals with the evaluation of breeding success. Currently, we evaluate this by using the numbers of breeding females and juveniles that are captured at our monitoring sites. However, we suspect that this measure is biased. It is likely that the willingness of gravid females to enter our traps varies among species and that the juveniles entering our traps may not be locally hatched. Thus, we have built a partnership with the American Museum of Natural History at the Southwestern Research Station in the Chiricahua Mountains of southeastern Arizona. We are conducting nesting success studies to help develop a more reliable measure of breeding success for hummingbird. The study's objectives are to:

Determine if there are specific habitat requirements for nesting of hummingbird species in this zone.
Determine if grazing alters the habitat sufficiently to effect change in nesting success.

Harold Greeney from Mexico is an excellent nest finder and has already found many Black-chinned and Magnificent Hummingbird nests. We will report on this study as it progresses.

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Energetics of Flight in Hummingbirds

Question: Wht is the energetic cost of extended flight in hummingbirds.

Summary: Dr. Donald Powers, George Fox University, working at the Southwestern Research Station in the Chiricahua Mountains and at Dr. Susan Wethington’s station in the Patagonia Mountains, will continue his studies on the energetic cost of hummingbird flight in collaboration with the Hummingbird Monitoring Network. Because of their small size and therefore the need for high metabolic rates to maintain body temperature, metabolism of hummingbirds has been a subject of study for many years. But many aspects of the cost of extended flight are still unknown, especially during flight-feather molt, when birds are flying in wind, when birds move over long distances, and when they fly at varying ambient temperatures. This study will concentrate on the effect of wing feather molt on the energetic cost of flight of free-living hummingbirds. Two students will partner with Dr. Powers in the project during the summer of 2007.

The following study is an integral part of the Energetics study above.

Respiratory Evaporative Water Loss During Hover Flight in Hummingbirds

Question: What is the extent of water loss from the respiratory system of hummingbirds during flight.

Summary: Dr. Philip W. Getsinger, Donald R. Powers, Bret W. Tobalske, and Susan M. Wethington are studying the loss of water from the respiratory system of hummingbirds during hovering flight. This is a collaborative effort among George Fox University, University of Portland, and the Hummingbird Monitoring Network. All birds (and mammals) that live in dry climates inhale very dry air. The air comes in contact with the moist respiratory membranes in the lungs and air sacs of birds. The moisture evaporates into the dry air and the water vapor is expelled with each breath. Over time, this creates a significant water loss for the bird. During flight, respiration increases and so does respiratory evaporative water loss. Studies were done on free-living hummingbirds whose water loss can be determined by analysis of the air exhaled during hovering flight while feeding at a special feeder that collects the expired air. Results to date show that water loss increases linearly with feeding time, that water loss increases linearly with increasing ambient temperature, and is greater in hovering as compared with forward flight. They also found out that there is a difference in water loss between sexes of the same species that might be related to wing loading (the relative amount of flight generating surface of the wings). Hummingbirds have much greater rates of water loss than that of other small birds studied (e.g. the Verdin). Studies are continuing.

The use of stable isotopes to estimate the wintering ranges of Rufous Hummingbirds.

Question: Where do populations of Rufous Hummingbirds that breed in different areas of British Columbia overwinter?

Summary: Jonathan Moran, professor at Royal Roads University in British Columbia, is undertaking a study to determine if different populations of breeding Rufous Hummingbirds in southern British Columbia overwinter in the same or different areas. The reason for the study is that disjunct populations show markedly different trends in populations over time. Populations nesting on Vancouver Island appear to more stable than those nesting on the western mainland that are in a long-term state of decline.

The Rufous Hummingbird is a Species of Continental Importance as designated on the Partners in Flight watch list and is also on the National Audubon Society’s Watchlist as a Species in Decline. HMN banders in Arizona have documented a decline in numbers of Rufous Hummingbirds over the last five years of monitoring.

The study is based on the fact that Deuterium, a naturally-occurring stable isotope of Hydrogen, varies in relative abundance with rainfall and temperature so that there is a gradient from Northwest to Southeast in North America. The deuterium is contained in all living tissues and therefore in the feathers of hummingbirds. By removing and analyzing a single feather from a bird, we can determine the latitude at which the feather was grown – and therefore where the bird was during its annual molt. Rufous Hummingbirds molt their flight feathers in late winter before their annual northward migration. By sampling birds both on the migration route and on the breeding grounds, we can determine at what latitude the birds spent the winter. This may show that the two populations (or more) of Rufous Hummingbirds breeding in British Columbia overwinter in different areas and that factors in the wintering areas may be causing the decline of the western mainland population.