Research Article Evidence for Regionally Synchronized Cycles in Texas Quail Population Dynamics JEFFREY J. LUSK, 1,2 Department of Forestry, Oklahoma State University, Stillwater, OK 74078, USA FRED S. GUTHERY, Department of Forestry, Oklahoma State University, Stillwater, OK 74078, USA MARKUS J. PETERSON, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843, USA STEPHEN J. DEMASO, Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, TX 78744, USA ABSTRACT Knowledge of the possible role of cyclic behavior in wildlife dynamics assists in understanding and managing populations. Using spectrum analysis, we analyzed time series (1978–2002) on the abundance of northern bobwhites (Colinus virginianus) and scaled quail (Callipepla squamata) in several ecological regions in Texas, USA, to test for the presence of cycles; we also tested whether drought severity (Modified Palmer Drought Severity Index) exhibited cyclic dynamics and whether quail and drought cycles were synchronized among regions. We found evidence of population cyclicity in all ecoregions we tested (5 for bobwhites, 4 for scaled quail) based on both Texas Parks and Wildlife and North American Breeding Bird Survey count data. Periods of the observed cycles generally were 5–6 years (bobwhites) or 2–3 years (scaled quail), depending on ecoregion and data source. Cyclicity was most pronounced for bobwhites in the Rolling Plains (north TX) and the South Texas Plains. The Palmer Index exhibited a roughly 5-year cycle in 5 of 6 regions we tested. A 5-year bobwhite and Palmer Index cycle were synchronous in 3 contiguous ecoregions totaling 27,200,000 ha. Wet–dry cycles seemed to synchronize bobwhite cycles in Texas. Our results suggest that habitat manipulations aimed at improving habitat conditions during dry periods, such as reducing livestock stocking rates, could provide ground cover similar to that available in wet periods. ( JOURNAL OF WILDLIFE MANAGEMENT 71(3):837–843; 2007) DOI: 10.2193/2005-729 KEY WORDS Callipepla squamata, Colinus virginianus, cycles, northern bobwhites, Palmer Drought Severity Index, population dynamics, scaled quail, synchrony. Cyclicity in wildlife dynamics has intrigued humankind since the sixteenth century, when ‘‘reliable men of great probity’’ observed Norwegian lemmings (Lemmus sp.) falling from the sky in large numbers on a 4-year cycle (Elton 1927:133). Cyclicity in North American grouse (Tetraonidae) has long been recognized (Leopold 1931, Schorger 1944, Darrow 1947). Northern bobwhites (Colinus virginanus) were early on considered noncyclic and the dynamic behavior of southwestern quail was unstudied (Leopold 1933). However, Errington (1945) conjectured that wild higher vertebrates of small to moderate size, including bobwhites, showed some semblance of 10-year periodicity in North America. Preno and Labisky (1971) noted, without formal analysis, an approximate 5-year cycle of bobwhites in Illinois, USA, based on calling-male surveys during 1956–1969. Subsequently, cyclicity in quail dynamics has been assessed with greater quantitative rigor. Roseberry and Klimstra (1984) analyzed cyclicity in bobwhite dynamics in southern Illinois and identified an 8–10-year cycle that was coincident with the nodal cycle of the moon (Archibald 1977). In a more comprehensive examination of 73 time series largely on bobwhites in the eastern United States, 37 times series showed evidence of cyclicity with periods ranging from 4 to 17 years (Thogmartin et al. 2002). Excepting Williams (1963) and Thogmartin et al. (2002), who reported cycles for California quail (Callipepla californicus), we know of no analysis for species of New World quails other than bobwhites. Proposed causes of population cycles are numerous and involve both intrinsic and extrinsic factors, although some form of density dependence seems necessary for cycles to develop in a population (May 1974, Kendall et al. 1999). Extrinsic factors proposed to explain cyclic trends include predator–prey and host–parasite interactions and environ- mental variation. Current theory holds that density-depend- ent factors are responsible for population cycles, whereas density-independent, extrinsic factors can alter the perio- dicity of the cycles and synchrony among spatially disjunct populations. The Moran effect (Moran 1953, Koenig 1999) has been proposed as such a density-independent, extrinsic mechanism leading to synchrony in population dynamics. Moran (1953) suggested that correlations in fluctuations among spatially disjunct populations (i.e., population synchrony) should equal correlations in environmental noise (e.g., weather) experienced by all populations, if the populations are regulated by the same density-dependent processes. Annual variation in weather variables strongly influences quail dynamics, especially in semiarid environments. For example, the timing and quantity of precipitation affect the productivity of Montezuma quail (Cyrtonyx montezumae; Brown 1979), Gambel’s quail (Callipepla gambelii; Swank and Gallizioli 1954), northern bobwhites (Kiel 1976), and scaled quail (Callipepla squamata; Campbell et al. 1973). Likewise, lower temperatures during a breeding season generally foster production, whereas higher temperatures tend to suppress it (Heffelfinger et al. 1999, Guthery et al. 2002). Thus, it is 1 E-mail: jeff.lusk@ngpc.ne.gov 2 Present address: Nebraska Game & Parks Commission, 2200 N. 33rd Street, Lincoln, NE 68503, USA Lusk et al.  Bobwhite Population Cycles 837