Virginia et al, I suspect the answer to your question is complicated and involves more than one factor. In reading about our two jackrabbit species in Mammals of Colorado (by Fitzgerald, Meaney, and Armstrong), some of the more pertinent factors determining their population levels seem to be:
Populations naturally go thru wide fluctuations (Black-tailed on about 5-year cycles, White-tailed on about 10). White-tails are probably the more common species on the West Slope, but encroachment on their former dominance west of the Divide by Black-tails has been noted. White-tails suffer more from loss of native vegetation than Black-tails. Juvenile jackrabbit mortality is high during any year (55-70%). Given their high reproductive capacity (up to 5 broods a year, with 1.9 to 6.4 young per brood), if you do the math, a slight increase or decrease in survival could lead to wide population swings. Both eat a lot of grasses and forbs in the summer, a lot of shrubs and other woody browse plants in the winter. Coyotes, foxes, badgers, eagles and humans are the main predators (between 1893 and 1985, organized hunts in Prowers and Las Animas Counties reported killing 32,000 rabbits!). 1 Cow equals 74 Black-tailed Jackrabbits in terms of forage consumption (5.8 to 30 jackrabbits = 1 domestic sheep): both from studies in Arizona and Utah. My personal comment would be that I consider any sighting of a White-tailed Jackrabbit these days, particularly on the eastern plains, to be noteworthy. Apparently this did not used to be the case, but with all the modifications of the plains by people (agriculture, housing developments, oil/gas, etc.), the Black-tailed is predominating. I would also say that human sprawl seems to favor an increase of free-roaming domestic and feral dogs, foxes, and coyote, which probably isn't good for rabbits of any kind. Dave Leatherman Fort Collins From: VIRGINIA SIMMONS Sent: Sunday, April 08, 2012 2:49 AM To: [email protected] Subject: [cobirds] Nonbirding question When birdwatching in rural areas in Colorado in Colorado, have you observed a decline in numbers of Jackrabbits in the past 15-20 years? If so, do you have any explanation, anecdotal or scientific, such as predators, disease, climate, human activity, habitat change? Thank you. Virginia Simmons, Del Norte -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
