Scoutdog,
I certainly won't claim comprehensive knowledge of the situation in Colorado, but there have been analyses of the impacts of reduced buck harvest on fawn ratios and population productivity. There's a brief discussion of the CO situation on muledeernet.org (
http://www.muledeernet.org/statuscolorado.htm) and a technical paper in the Wildlife Society Bulletin (Bishop, C. J., et al. 2005 Effect of limited antlered harvest on
mule deer sex and age ratios. Wildlife Society Bulletin 33:662-668). The basic conclusions thus far have been...
From the CO status report on muledeernet: "Although a full analysis is still pending, there does not appear to be a clear relationship between reduced buck harvest and posthunt fawn:doe ratios (i.e., fawns/100 does) in Colorado. In some units where major reductions in hunter numbers resulted in large increases in buck:doe ratios, fawn:doe ratios have remained low. Conversely, in some units with only minor reductions in hunter numbers and small increases in buck:doe ratios, fawn:doe ratios have increased considerably. In many units, observed fawn:doe ratios went from being consistently low in the late 1990?s to showing considerable year to year variation since 2000."
and
"The decline in Colorado?s deer populations in the 1990?s appeared to result primarily from reduced early fawn survival. During this period, posthunt fawn:doe ratios steadily declined in most of the state with the exception of the eastern plains. Radio-telemetry studies of early fawn mortality in western Colorado indicated that disease and malnutrition were at least as important as predation in reducing early fawn survival. Another study showed that improved nutrition and condition of does during the winter resulted in higher survival of fawns the following summer. Improved nutrition and condition of fawns during the winter resulted in highly significant increases in survival. The predation rate on fawns was inversely related to fawn nutritional status and condition."
From a paper at the 2007 Deer/Elk Workshop (Bergman et al.):
"Despite an overall trend of increasing posthunt fawn:doe ratios between 1999 and 2006, our post hoc analysis indicates that the statewide limited draw system has likely had a negative impact on fawn:doe ratios. However, between 1999-2006, the total mule deer population as well as buck:doe ratios have steadily risen as a result of limiting buck licenses statewide. Our analysis indicates that the majority of population growth is attributable to the mature buck population segment and there is little or no indication that herd productivity has been improved by harvest management actions."
From Bishop et al.: "Based on our analysis, factors other than buck harvest were regulating population productivity, and limiting buck harvest to enhance fawn recruitment is not justified in Colorado. Limited buck harvest should be considered an issue of quality hunting opportunity rather than deer productivity."
I agree that increasing bull ratios and therefore the number of mature bulls can create an earlier, shorter rut, and a subsequent earlier, shorter calving period. And yes the logical consequence is larger calves going into winter and greater calf survival. In fact, I have been a promoter (albeit a fairly cautious one) of spike-only hunts, in part because of this reasoning (there are other good reasons for spike-only as well). But research has also failed to demonstrate this effect in managed elk populations (e.g., Bender, L. C. et al. 2002. Effects of Open-Entry Spike-Bull, Limited-Entry Branched-Bull Harvesting on Elk Composition in Washington. Wildlife Society Bulletin 30:1078-1084). They actually documented a reduction in calf ratios under the higher bull ratios generated through spike-only/limited branch bull hunting and contend cow nutritional condition has much greater influence on calf production and survival than bull ratios.
Sometimes our most logical thoughts are rendered invalid by real-world complexity and interactions. That's why research of "common sense" and "logical assumptions" is an important part of the learning and management process.
Tom Keegan
IDFG Salmon Region Wildlife Manager