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The lower South Platte River (SPR) corridor Greeley to the state line has historically supported the highest numbers of wintering ducks and highest hunter numbers and duck harvest of any region in the Colorado. Over the past decade there has been increasing concern that harvest pressure has led to reduced numbers of wintering ducks and low harvest success, which could in turn lead to lower hunter satisfaction and declining hunter recruitment and retention. These concerns have prompted discussions about creating refuge areas and implementing more restrictive hunting regulations on public and private lands along the SPR in an effort to increase the quality of duck hunting. However, decisions about the most effective management actions to take were hampered by a lack of basic information about duck use of SPR habitats and hunter activity, success, and satisfaction.   

During the 2004-05 and 2005-06 waterfowl seasons, baseline information was collected on patterns of waterfowl abundance and distribution along the SPR corridor during waterfowl seasons, the range of hunting activity on public and private lands, use of and crowding on public hunting areas, waterfowl harvest, and hunter perceptions and preferences about hunting quality along the SPR, primarily on public lands. These results were used to formulate directed field research projects to examine specific questions about duck hunting management.

Mallard Behavioral Response to Hunting Disturbance and Winter Survival
During the 2006-2007 and 2007-2008 hunting seasons, the Colorado Division of Wildlife (now Colorado Parks and Wildlife) and Colorado State University supported a graduate student, Josh Dooley, who conducted a study on mallard (Anas platyrhynchos) response to hunting disturbance and winter survival along the SPR corridor. Mallards were radio-marked and monitored throughout the hunting season, and shooting and walk-in disturbances were administered to radio-marked mallards to determine their response. Key results include:

• Radio-marked mallards redistributed on a small spatial scale after disturbance
  • Average distance ≈ 3 km
  • 16 of 276 flew > 10 km
  • No radio-marked mallard completed vacated the study area
• Use of the South Platte River channel was minimal for radio-marked until late in the hunting season when off-river habitats were frozen
  • Only 1 of 126 radio-marked mallards disturbed on off-river habitat went to the South Platte River during September, October, and November
  • Radio-marked mallards disturbed on off-river habitat were 24 times more likely to use the river channel in December, January, and February
• Many mallards quickly returned to areas where they were disturbed
  • 70–75% of radio-marked mallards returned to areas of disturbance at least one time within the following 5 days
    • Most radio-marked mallards that did return, returned within 1 day
    • Few returned the afternoon of disturbance
  • Overall waterfowl (i.e., all ducks and geese) occupancy and abundance levels on disturbed wetlands returned to pre-disturbance levels within 1 day
• There were minimal differences in behavioral responses of radio-marked mallards between shooting and walk-in disturbance
• Most radio-marked and legbanded mallards remained in the study area throughout the winter
  • 89% of radio-marked mallards and 86% of legbanded mallards that were harvested were shot within the study area
  • Low proportions of radio-marked mallards went missing (3–15%)
• Hunting was the main cause of winter mortality
  • 67% hunting mortality vs. 33% non-hunting mortality
  • Survival was lower during hunting seasons vs. non-hunting periods, especially opening weekends
    • Survival was lowest during the first 2–3 weekends of hunting splits
      • 49% of all hunting mortality occurred within the first 3 weeks of hunting seasons; 37% during the first 3 weekends
    • Hunting mortality was higher for males than females
• Hunting mortality of radio-marked mallards occurred on both public (43%) and private lands (57%)
• Winter survival was lower for radio-marked mallards in poorer body condition at capture
• Daily survival was lower during periods of high accumulated snowfall (≈ 10 in) and low temperatures (< 10° F)

Full results of this study are available in a thesis, “Mallard response to experimental human disturbance and non-breeding survival along the South Platte River in Colorado ”, by Joshua Dooley (2008).

Evaluating Waterfowl and Small Game Hunting Regulations on State Wildlife Areas
Restrictive hunting regulations (e.g., access only by reservation and only 3-4 days per week) are used on some SWAs along the SPR corridor in an effort to improve hunting quality, whereas other SWAs have no property-specific restrictions in an effort to maximize access to hunting opportunity. However, no formal evaluation of the effectiveness of property-specific hunting restrictions has ever been conducted. 

Beginning with the 2008-2009 duck hunting season, a study was initiated to compare waterfowl and small game hunter success, hunter activity, and hunter satisfaction between a set of SWAs with restrictive hunting regulations and a set of SWAs without restrictive hunting regulations. We will also examine how the influence of regulations varies among SWAs with differing habitat conditions. 

Restrictive regulations include:

1. Reservations are required for hunting access (a limited number of parties on the property, with no more than 4 hunters per party)
2. All parties must leave the property by 2 p.m.
3. Hunting is allowed only on Saturdays, Sundays, Wednesdays, and legal holidays
4. Hunting parties are assigned to specific areas on the property. 

These restrictions apply only to waterfowl and small game hunting during the regular duck hunting season. Study SWAs were paired by habitat type and regulations were assigned to each property:

1		Hunting Season Regulations (R=Restricted U=Unrestricted)
Type	State Wildlife Area	2008	2009	2010	2011	2012	2013
Off-river channel	Jackson Lake	R	R	R	U	U	U
	Red Lion	U	U	U	R	R	R
On-channel small property	Overland Trail	R	R	R	U	U	U
	Atwood	U	U	U	R	R	R
On-channel large property	Bravo	R	R	R	U	U	U
	Jean K. Tool & Brush	U	U	U	R	R	R

Regulation assignments will be switched beginning with the 2011-2012 season, in order to account for site-specific differences between properties in each pair.

Check stations have been established at these 7 SWAs, and access to these areas is from designated parking areas only. During the regular duck hunting season, all waterfowl and small game hunters on these SWAs are required to check out at the check station before leaving the property. Check station attendants interview all hunters and record information on their hunting experience and methods, harvest success, and satisfaction. These results will be compared for each pair of SWAs annually. Monthly aerial counts of waterfowl along the SPR corridor are also being conducted to track changes in overall numbers and distribution of ducks throughout the hunting season each year.

This study is planned to continue through the 2013-2014 hunting season. Results will be used to develop future recommendations for waterfowl and small game hunting regulations on SWAs in northeastern Colorado. See the 2012 progress report  for results from the first year of the study.