Sensitivity Analyses of a Population Projection Model of Ring-Necked Pheasants

Abstract

A large literature exists on population dynamics of ring‐necked pheasant (Phasianus colchicus) in North America, but there has not been an attempt to formulate a matrix model nor a sensitivity analysis of the relationships between vital rates and population finite growth rate (Λ) that can be used to guide management. We summarized demographic data available from a 5‐year field study in Iowa, USA, collected in Kossuth County (low composition of perennial habitat) and Palo Alto County (high composition of perennial habitat) into a 2‐stage (young and adult) matrix projection model. We estimated Λ1 (the dominant eigenvalue of the deterministic matrix), the stable age distribution (ω), relative reproductive value vector (n̈), other demographic parameters, and Λiid, a bootstrap estimate of growth that includes interannual variation in life history parameters. We analyzed the relative importance of vital rates on population growth rate using sensitivity and elasticity of both matrix elements and lower‐level parameters such as winter survival and nest success. We first characterized general life history using averaged data from both areas and all years that yielded Λ1 = 1.086, and a stable stage distribution of. Minimum success of the initial nesting attempt (H1) that would maintain Λ ≥ 1 under average conditions was estimated to be 42%. Changes in Λ1 were most sensitive to survival of chicks during brood rearing (SB), followed in importance by survival during the subsequent winter (SW), followed by H1. We followed the general analyses with analyses that helped us to focus on the differences in the landscapes of northwest Iowa. Λiid was ≥1 in only 9% of simulations of data from Kossuth whereas estimated Λiid was ≥1 in 88% of simulations from Palo Alto. Our analyses of the relative importance and interactions between SB, SW, and total recruitment (M, including H1 and renesting), if combined with data more specific to a local area, would guide management aimed at affecting multiple life history stages whose relative importance will vary across the landscape.

Mid‐contract management of Conservation Reserve Program grasslands provides benefits for ring‐necked pheasant nest and brood survival

“…Also, our simulation model predicted that productivity, a function of nest success and brood success, and population growth rates were dramatically greater when the simulated landscape contained ≥ 50% DI-CRP. Our nest success rate in unmanaged grasslands (31%) was similar to rates from Illinois reported by Warner et al (1987) but below the benchmark stated in Clark et al (2008) of 42% nest success, which they suggested is needed to maintain a stable population under average conditions. Certainly, sub-optimal nest success in unmanaged, low diversity grasslands could be partially responsible for the recent decline in pheasant numbers throughout most of the Great Plains states, even after the introduction of CRP Rodgers 1999).…”

“…A landscape-level approach to pheasant habitat management enhances nest and brood survival by creating a heterogeneous landscape, at both the macro-and microhabitat levels. Such heterogeneity may cause the greatest effects on pheasant populations (Clark et al 2008). Landscape-level efforts are labor intensive, as they require assistance and consultation with many landowners.…”

Why do many pheasants released in the UK die, and how can we best reduce their natural mortality?

“…In the relatively few releases of reared birds in the USA, where management such as predator control is rare, mortality may reach levels of 60-85% in the first 2 months post release (Burger 1964;Hessler et al 1970;Krauss et al 1987). These mortality levels compare poorly to those of 2-month-old wild-born birds that have survived to a similar period (September-April) in the USA, which range from 43 to 48% (Clark et al 2008).…”

Factors influencing reproductive performance of northern bobwhite in South Florida

“…Although nesting success seems to be the key reproductive parameter in many short-lived species of birds (see Clark and Martin 2007 for a review), the relative contribution of various components of reproduction on Communicated by C. Gortázar Electronic supplementary material The online version of this article (doi:10.1007/s10344-010-0479-5) contains supplementary material, which is available to authorized users. overall reproductive success and population growth rate remains poorly explored in most species (but see Wisdom and Mills 1997;Bernard-Laurent and Leonard 2000;Clark et al 2008). Furthermore, reproductive parameters can vary substantially over space and time, and understanding causes and consequences of such variations is important for understanding population dynamics, regulation, and persistence (Frederiksen et al 2005;Jenouvrier et al 2005;Saether et al 2006).…”