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Ecologists Map Mule Deer Reproduction with NASA Satellites
National Park Service

Utah State University ecologists recently partnered with NASA to study how the timing of mule deer fawning tracks vegetation growth in parts of the Intermountain West.


Dr. David Stoner and his colleagues recently published a study in the open access scientific journal PLOS ONE about how mule deer respond to climate patterns in Utah and Northern Arizona. Findings from the paper indicate that when mule deer give birth closely tracks when vegetation growth and abundance is at its peak.

“What we found was that deer are hitting this optimal point just after the start of season but just before the peak of season, and that on average this represents the optimal time for giving birth, supporting fetal growth and supporting lactation in the early phases of fawn growth,” says Stoner. Not all mule deer will hit this moving time window (which varies from North to South and year to year) but the fact that most do is an adaptation that helps mule deer provide for their young and helps ecologists predict how mule deer will respond to a changing climate.


"Our eyes, are sort of our own satellites."

Much of the data used in the research was collected by NASA satellites. That may seem an unusual tool for an ecologist, but it is really just a matter of scale. “Our eyes, are sort of our own satellites -- we remotely sense information -- but satellites do it from a higher vantage point and have the ability to see parts outside the visible spectrum,” says NASA scientist Dr. Allison Leidner.


Leidner says that NASA’s “eye in the sky” can monitor many of the same things that ecologists also measure from the ground:



“Fundamentally, what we call passive satellites, or passive remote sensing does, is looks at the reflectance of sunlight on the earth’s surface and measures that. Plants absorb red and blue light and they reflect green light. They also reflect a lot of light in the near-infrared. So, we use that information about the amount of light that’s reflected and the amount of light that’s absorbed to build vegetation indices to see how green the surface of the earth is and how that changes through time.”


"The strength of the climate signal in deer natural history is overwhelming."

Such vegetation indices are key to Stoner’s study. The papers’ findings show that the changing greenness of our planet can tell us a lot about our changing climate and how our wildlife are likely to respond. In the future, where mule deer are likely to be found and in what abundance will depend in large part on how a changing climate alters when, and to what extent, their food grows and gets green.


“The strength of the climate signal in deer natural history is overwhelming. I mean it is very clear that climate is really an extremely important factor in producing these patterns,” says Stoner.




The scientific paper referenced in this article, Ungulate Reproductive Parameters Track Satellite Observations of Plant Phenology across Latitude and Climatological Regimes, can be accessed for free from the PLOS ONE website.