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Morgart-Sheppard Letter

Editor: Birdscapes’ Fall 2002 Issue featured an article about the status of Sonoran pronghorns by Ben Ikenson. As a result, I received an e-mail from Jay Sheppard, asking a question about the movement of pronghorns in relation to rain storms. I forwarded the message to Dr. John Morgart, the article’s contact person, for a response. I thought the exchange would be of interest to you. I have their permission to print the correspondence.

I just read your nice piece in the latest Birdscapes re the Sonoran pronghorn. I thought I might relay an observation I made in early Fall 1967. I was flying from Tucson to L.A. As we gained altitude and headed west, I could look down and clearly see where all the rain storms had crisscrossed the desert that past summer. What a truly interesting sight: green rivers of vegetation a mile or two wide, moving first in one direction, and then altering course 5 to10 degrees to the right or left for another dozen miles or so. Most petered out before crossing the Colorado. Many crossed the paths of others and that created an extra bright green patch. All were headed in the typical SE to NW general direction. Obviously, our flight path took us almost directly over CPNWR [Cabeza Prieta National Wildlife Refuge]. . . a great area where I have spent a small amount of time birdwatching, collecting beetles, etc.

Since I did a lot of my early studies in birds but also in other verts and insects out on the deserts of the Southwest, I always remembered that trip. I am sure your folks have long known about this and have satellite and other imagery to follow the storm tracks each summer and monitor the pronghorns' movements. I would assume that they have a great sense of smell and can follow the storm tracks from some distance away?

Jay

Hi Jay, I read with interest your message to my friend Dee. Your observation of some years ago was very astute. Sonoran pronghorn are indeed very aware of summer monsoon storms and will quickly move 20 to 40 miles in response to these patchy and often localized events. This is a behavioral trait we hope to exploit with our ongoing efforts to recover the population. Specifically, the [U.S. Fish and Wildlife] Service and its partners are in the process of placing a series of small forage enhancement plots across the range of the Sonoran pronghorn. These areas will be sprinkler-irrigated during drought periods to mimic natural rainfall patterns. Our hope is that the native seed bank in the soil will respond to the extra moisture during these critical times and provide a nutritious source of green forage for pronghorn and their fawns.

We assume, but don't know for sure, that the animals respond to a combination of visual and olfactory cues when they move into seasonal green-up areas. Given the often scattered and widely located nature of these rainfall events, I can't help but think that a highly developed sense of smell is of key importance in helping pronghorn locate these areas, however. For example, I was flying around the Cabeza Prieta National Wildlife Refuge in a helicopter last week, surveying for desert bighorn sheep. Off to the west 2 to 3 miles, a small rain cell dumped more than an inch of precipitation in an approximately 1-square-mile area. So much rain fell in a short period of time, that the entire area was covered with sheet flow, and all the washes ran. Admittedly the wind was in my favor, but even at this distance, with the pounding of the rotor wash of the helicopter all around (and an admittedly inferior sense of smell as compared to a pronghorn), I could clearly discern the indescribably clean smell of the Sonoran Desert and creosotebush after a thunderstorm.

Anyway, hopefully this answers your question. If there's anything else you would like to know about Sonoran pronghorn and I can help, please don't hesitate to contact me.

Best regards, John