Jeffrey J. Lusk

The fall of the null hypothesis: Liabilities and opportunities

The collapse of null hypothesis significance testing as a statistical paradigm has created liabilities and opportunities in wildlife science. One liability is that some formalism for statistical hypothesis testing, such as likelihood with information theory, will simply replace null hypothesis significance testing as a rote approach to wildlife science. The principal intellectual instrument of the scientist remains the research hypothesis, not the statistical hypothesis. Accordingly, 1 opportunity arising from a change of statistical paradigms is that the research hypothesis will move to the foreground of wildlife science, the statistical hypothesis to the background. A second opportunity is a broadening of the suite of inferential methods considered orthodox in wildlife science. Realization of these opportunities should help wildlife scientists resist the social tendency to allow tools (means, statistical models) to supplant the search for reliable knowledge (end) as the benchmark of scientific endeavor. Science of the highest order, including virtually all discoveries that humankind extols today, is possible without the statistical hypothesis, but not without the research hypothesis.

Factors Influencing Northern Bobwhite Nest‐Site Selection and Fate

Abstract Understanding factors underlying nest-site selection is important for effective conservation and management of a declining and economically important species. We measured vegetation characteristics at nest sites of northern bobwhites (Colinus virginianus; hereafter, bobwhites) and at random points in the Texas Panhandle. We used these data to develop a neural network classification model for predicting nest-site suitability. We also compared the characteristics of successful nests with those of failed nests using the bootstrapping method. We monitored a subset of nests using video cameras during incubation and for 3 days postcompletion (succeeded or failed) to determine nest fate, cause of fate, and nest activity after completion. Nest-canopy height, percent shrub cover, and bare-ground exposure were important vegetation characteristics influencing nest-site selection. Sites became more suitable as canopy height exceeded 40 cm, shrub cover exceeded 25%, and as bare-ground exposure fell below 30%. Successful nests had higher canopies and more shrub cover than failed nests, but successful nests had more bare ground than failed nests. Nest visits were common at monitored nests after nest completion (failed, successful). Most visitors were adult bobwhites, but other species also visited nests. Such visits might bias the determination of nest fate if the determination is based on nest remains, especially if nests are not monitored daily. Bobwhites might select nest sites to maximize nest concealment compared with random locations.

Radiotelemetry studies: are we radio-handicapping northern bobwhites?

Abstract Having become suspicious of telemetry-based survival rates reported for northern bobwhites (Colinus virginianus), we surveyed the published record to determine whether reported survival rates were consistent with empirical expectations of production, for which there exists a vast database. If the production (juvenile/adult) required to stabilize a population at a reported or inferred annual survival rate was ≤7, we deemed the reported survival rate reasonable; otherwise, we deemed it not reasonable. We obtained 58 estimates of survival rates for unique points in space and time; 83% of these were not reasonable (apparently biased low). These results and supporting information strongly suggest (but do not necessarily prove) that radio packages (harness, transmitter, antenna) somehow handicap bobwhites. We recommend that researchers be extremely skeptical of telemetry data, plan telemetry studies such that independent data on population performance are available for comparison with telemetry estimates, and discuss the demographic implications of telemetry estimates. We also suggest that radiotelemetry might not always be appropriate for a given research question and that alternative methods be employed whenever possible.

Survival and cause-specific mortality of northern bobwhites in western Oklahoma

Abstract We present descriptive data on survival and cause-specific mortality of northern bobwhites (Colinus virginianus) in western Oklahoma, USA, during 1991–2002. We captured and radiomarked 2,647 bobwhites (286 adult [ad] M, 1,064 juvenile [juv] M, 185 ad F, and 1,049 juv F) to obtain estimates. We estimated that annual survival (Nov–Oct) averaged 0.068 ± 0.018 (SE) and ranged between 0.018 ± 0.048 and 0.211 ± 0.038. We pooled data over the study period and found that sex–age classes survived at similar rates. We estimated average annual isolated rates of bobwhite mortality (rates in the absence of other causes) to be 0.63 ± 0.027 from raptor predation, 0.45 ± 0.021 from mammal predation, and 0.45 ± 0.043 from harvest. Under the additive theorem of probability, the isolated rates translated to an average annual mortality rate of 0.88 ± 0.017. The bobwhite population had variable and sometimes low survival in November–February inclusive. Low monthly survival (<0.5, n = 7) during winter was due primarily to harvest (0.57 ± 0.099 losses/known-fate individual) and raptor predation (0.25 ± 0.051 losses/known-fate individual). We discuss evidence indicating that radiotransmitters handicapped bobwhites and resulted in survival estimates biased low and to uncertainty in interpretation of cause-specific mortality.

Northern bobwhite (Colinus virginianus) abundance in relation to yearly weather and long-term climate patterns

Abstract We used a multilayered, backpropagation neural network to investigate the relative effects of yearly weather and long-term climate patterns on the abundance of northern bobwhites (Colinus virginianus: hereafter, bobwhite) in Oklahoma, USA. Bobwhite populations have been declining for several decades across the United States, and predicted global climate change might accelerate the rate of decline. We were interested in whether bobwhite abundance was more responsive to yearly precipitation and temperature, or to annual deviations from long-term mean climate patterns. We used roadside count data collected over a 6 year period (1991–1997) by the Oklahoma Department of Wildlife Conservation as a measure of bobwhite abundance. We standardized quail counts among counties by calculating the standard normal deviate for each county. Weather data were obtained from weather stations closest to the roadside-count route. We had 280 training cases and 68 test-validation cases. Two data sets were constructed: one using yearly weather data (actual rainfall and temperature) and the second using annual deviations from long-term mean values. We conducted simulation analyses to determine the nature of the relationship between each dependent variable and the standardized bobwhite counts. A neural network with eight neurons was most efficient for the yearly weather data, accounting for 25% of the variation in the training data. The adjusted sum-of-squares for this model was 2.42. A four-neuron network was selected for the deviation-from-normal data set, accounting for 23% of the variation in the training data. The adjusted sum-of-squares for the deviation model was 1.44, indicating it performed better than the model for yearly weather patterns. Deviation from long-term mean July and August temperatures combined contributed 31.5% to the climate networks predictions, and deviations from mean winter, spring, and summer precipitation combined contributed 42.8% to the networks predictions. As July temperature increased over the long-term mean, the number of bobwhites counted increased over the route mean, but the relationship decelerated at high July temperatures. Predicted increases in bobwhites counted were highest when August temperatures were below the mean and decreased rapidly for all temperatures greater than the mean. Predicted bobwhite counts increased asymptotically as winter rain increased over the long-term mean, but were greatest at mean spring-rainfall amounts and at below average amounts of summer rainfall. We conclude that the absolute changes in yearly weather pattern predicted by some global change models will not have as great an impact on bobwhite abundance as will the magnitude of the deviations of these values from the climate bobwhites are adapted to in this portion of their range.

Relative abundance of bobwhites in relation to weather and land use

Weather and land use are important factors influencing the population dynamics of northern bobwhites (Colinus virginianus) in Texas and elsewhere. Using an artificial neural network, we studied the effects of these factors on an index of bobwhite abundance (hereafter, index) in 6 ecoregions in Texas. We used roadside-count data collected by the Texas Parks and Wildlife Department (TPWD) during 1978-1997. Weather variables were June, July, and August mean maximum temperatures, and winter (Dec-Feb), spring (Mar-May), summer (Jun-Aug), and fall (Sep-Nov) rainfall. We also included the proportion of county area in cultivation, the number of livestock per hectare of noncultivated land, and the previous years bobwhite count in the analyses. The data were partitioned into training and validation data sets prior to analyses. The neural model explained 65% of the variation in the training data (n = 72) and 61% of the variation in the validation data (n = 17). The most important variables contributing to network predictions were July temperature, fall rainfall, cattle density, and the previous years bob-white count. State-level simulation results indicated that the bobwhite index decreased with increasing June temperature and livestock density. The bobwhite index increased with July and August temperature, fall rainfall, and the previous years bobwhite count. Bobwhite abundance increased with the proportion of county area in cultivation up to approximately 20% cultivation and then declined. Winter, spring, and summer rainfall had little effect on the bobwhite index. Although many relationships appeared approximately linear or were decelerating, proportion of county area in cultivation and livestock density on noncultivated land showed strongly curvilinear responses. Therefore, cultivation up to approximately 20% of county area was beneficial, but the benefits disappeared as cultivation increased beyond this level. Further, at low livestock densities, between 0.15 and 0.40 head/ha, small increases in head/ha resulted in a decrease in the bobwhite index of 156.4%/head/ha. The results also indicated that a potential bias might exist in the survey protocol resulting in artificially inflated counts under some weather conditions.

LARK SPARROW (CHONDESTES GRAMMACUS) NEST-SITE SELECTION AND SUCCESS IN A MIXED-GRASS PRAIRIE

Abstract Lark Sparrows (Chondestes grammacus) are declining throughout most of their range. Effective management for this species is hampered because relatively little is known about nesting ecology. We studied habitat characteristics affecting Lark Sparrow nest-site selection and nest success at nine study pastures in a southern mixed-grass prairie in Oklahoma. We used a neural-network technique to discriminate between nest and random locations, and bootstrapping with 95% confidence intervals to compare habitat features of successful and unsuccessful nests. We quantified habitat features at the nest and random points during the breeding seasons of 1999 and 2000 among three grazing treatments (control, moderate, and heavy). We located 40 nests during two years of the study, for which crude nest-success was 26.3%. Most nests were located in either moderately grazed pasture (55%) or heavily grazed pasture (40%). The neural model correctly identified nest and random points 91% of the time. Percentage of structural cover, distance to nearest structural element, bare-ground exposure, and percentage of litter cover were the most important nest-site selection criteria according to the model. Simulation analysis indicated points were classified as nest sites if they were <270 cm from structural elements, <87% bare-ground exposure, <74% litter cover, and >9% structural cover. Successful nests had less bare-ground exposure (x̄ = 6.2 ± 1.9% [SE]) and more litter cover (x̄ = 18.0 ± 4.6%) compared to unsuccessful nests (x̄ = 17.5 ± 3.8% and 10.1 ± 1.6%, respectively). These results suggest that habitat management for Lark Sparrows in mixed-grass prairie should focus on creating abundant structural cover with moderate levels of litter accumulation and bare ground.

EFFECTS OF BAG LIMITS ON BOBWHITE HUNTERS AND HARVEST

Abstract Scientific management of quail harvest at the state level must be based on a clear understanding of the effects of hunting regulations on hunters and populations. Therefore, we assessed how reduction in bag limits would affect hunter opportunity and harvest rates of northern bobwhites (Colinus virginianus) in Oklahoma, USA, using harvest data from questionnaire surveys. Reductions in bag limits were regressive because reductions had relatively less effect on hunting opportunity and harvest rate at low populations than at high populations. Based on data primarily from Oklahoma and Missouri, we found that the negative binomial distribution described the probability of an integer bag (0, 1, 2, 3, … birds) if the mean and variance of daily bag were known. The negative binomial distribution provides a general method of assessing the effects of bag-limit reduction on hunting opportunity and harvest rates. The skill of the average hunter apparently declined as the statewide bobwhite population increased. Although hunting was self-regulatory in that the number of hunters declined as the bobwhite population declined, it was not self-regulatory when adjusted for the relative skill of hunters at low and high populations. We argue that fixed, relatively low bag limits established as a risk-aversive strategy for low populations of bobwhites may not necessarily have large impact on hunting opportunity with high populations.

Evidence for Regionally Synchronized Cycles in Texas Quail Population Dynamics

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.

REPRODUCTION BY NORTHERN BOBWHITES IN WESTERN OKLAHOMA

Abstract We studied northern bobwhites (Colinus virginianus) in western Oklahoma, USA, during the nesting seasons of 1992–2001. We obtained latitude-specific information on nesting biology and tested hypotheses on the cause of declines in clutch size with progression of the nesting season and on the phenological relation of first, second, and third nesting attempts. For pooled data on bobwhites alive during 15 April–15 September, 64 ± 6.5% of juvenile females (n = 56), 90 ± 10.0% of adult females (n = 9), 13 ± 4.1% of juveniles males (n = 68), and 41 ± 10.7% of adult males (n = 22) incubated ≥ 1 nest. Bobwhites that entered the reproduction period starting on 15 April (n = 229) accumulated 203 nesting attempts (male and female incubations), which translated to 1.7 attempts/hen for all hens that entered (n = 117) and 3.1 attempts/hen for hens that survived to 15 September (n = 65). Overall success for incubated nests (48 ± 2.8%, n = 331) was independent of sex-age class and nesting attempt (1, 2, 3), but it declined at a rate of 2.37%/year (95% CL = 1.10–3.64%/year) during the study. Clutch size declined by 1 egg for every 14–20 elapsed days in the nesting season and the rate of decline was independent of incubation attempt (1 or 2); this result suggests that lower clutch sizes later in the nest season were not necessarily a function of re-nesting. Ending of nest-incubation attempts (1, 2, 3) occurred within an 8-day period from 26 August–2 September. Our results implied that early-season nesting cover is a management concern and that high nest success is possible in the absence of nest predator suppression where abundant nest sites occur across the landscape.