Michael W. Hubbard

Analysis of Resource Selection Using Utilization Distributions

Abstract Often resource selection functions (RSFs) are developed by comparing resource attributes of used sites to unused or available ones. We present alternative approaches to the analysis of resource selection based on the utilization distribution (UD). Our objectives are to describe the rationale for estimation of RSFs based on UDs, offer advice about computing UDs and RSFs, and illustrate their use in resource selection studies. We discuss the 3 main factors that should be considered when using kernel UD-based estimates of space use: selection of bandwidth values, sample size versus precision of estimates, and UD shape and complexity. We present 3 case studies that demonstrate use of UDs in resource selection modeling. The first example demonstrates the general case of RSF estimation that uses multiple regression adjusted for spatial autocorrelation to relate UD estimates (i.e., the probability density function) to resource attributes. A second example, involving Poisson regression with an offset term, is presented as an alternative for modeling the relative frequency, or probability of use, within defined habitat units. This procedure uses the relative frequency of locations within a habitat unit as a surrogate of the UD and requires relatively fewer user-defined options in the modeling of resource selection. Last, we illustrate how the UD can also be used to enhance univariate resource selection analyses, such as compositional analysis, in cases where animals use their range nonrandomly. The UD helps overcome several common shortcomings of some other analytical techniques by treating the animal as the primary sampling unit, summarizing use in a continuous and probabilistic manner, and relying on the pattern of animal space use rather than using individual sampling points. However, several drawbacks are apparent when using the UD in resource selection analyses. Choice of UD estimator is important and sensitive to sample size and user-defined options, such as bandwidth and software selection. Extensions to these procedures could consider behavioral-based approaches and alternative techniques to estimate the UD directly.

SURVIVAL OF POSTFLEDGING GRASSLAND BIRDS IN MISSOURI

Abstract We describe survival patterns during the postfledging period for two species of grassland birds in Missouri. We monitored 155 radio-marked juvenile Dickcissels (Spiza americana) and 107 juvenile Eastern Meadowlarks (Sturnella magna; hereafter meadowlark) in southwestern Missouri, from 2002 to 2004. We used an information theoretic approach to evaluate support for biological, temporal, and spatial covariates on survival estimates using Cox proportional hazards models, and also identified cause-specific mortality. For Dickcissels, the model with biological covariates containing body mass had the lowest score using Akaikes information criterion, corrected for small sample sizes (AICc) and almost twice the support of the second-best model. For meadowlarks, the null model had the lowest AICc score, but the second-best model containing body mass was also competitive (within 2 AICc units), so we used the latter model for inference. Hazard ratios indicated that a 1 g increase in body mass was associated with a 3% (Dickcissels) and 2% (meadowlarks) reduction in the risk of death. The cumulative probability of surviving the study period (Dickcissels, 58 days, meadowlarks, 72 days) was 0.56 (95% CI: 0.49–0.65) for Dickcissels and 0.63 (95% CI: 0.54–0.74) for meadowlarks. Predation was the largest source of cause-specific mortality for both species and responsible for 56% (Dickcissels) and 70% (meadowlarks) of deaths. Snakes were the numerically dominant predator of juvenile Dickcissels, but there was not a numerically dominant predator of juvenile meadowlarks. Our results emphasize the importance of body condition on postfledging survival. Future studies should consider estimating postfledging survival rates within species across systems to understand the potential impacts of different predator communities on juvenile survival.

EFFECTS OF RADIO-TRANSMITTERS ON FECAL GLUCOCORTICOID LEVELS IN CAPTIVE DICKCISSELS

Abstract We determined the effects of a leg-harness transmitter on fecal glucocorticoid levels of wild male Dickcissels (Spiza americana) in captivity. During the postbreeding season of 2001, we captured 10 male Dickcissels in central Missouri and housed them in individual pens of an outdoor aviary. We radio-tagged five birds; the other five were captured and handled, but were not radio-tagged. We collected fecal samples every other day prior to attachment (31 July–21 August) and after attachment (24 August–20 September). Body condition and morphology were similar between control and transmitter-equipped birds. We observed a significant interaction between transmitter attachment and time since attachment. Compared to baseline levels, fecal glucocorticoid metabolites were significantly lower in control (6.1 ± 13.7 ng g−1) than transmitter-equipped (102.3 ± 13.7 ng g−1) birds during the first 24 hr after attachment. Although transmitter-equipped birds showed elevated fecal glucocorticoid levels, the response was acute and returned to baseline levels within 48 hr. Efecto de los Radiotransmisores en los Niveles de Glucocorticoides Fecales en Individuos Cautivos de Spiza americana Resumen. Determinamos los efectos de poner un transmisor con arnés de pata en los niveles de glucocorticoides fecales de machos silvestres de Spiza americana en cautiverio. Durante la temporada post-reproductiva de 2001, capturamos 10 individuos de S. americana en la parte central de Missouri y hospedamos estas aves en jaulas individuales que formaban parte de un aviario al aire libre. Pusimos radio-transmisores en sólo cinco de estos pájaros, los otros cinco sólo fueron capturados y manipulados. Colectamos muestras fecales en días alternados antes (31 julio–21 agosto) y después (24 agosto–20 septiembre) de poner los transmisores. La condición corporal y morfología fueron similares entre individuos con transmisor y individuos control. Observamos una interacción significativa entre poner los transmisores y el tiempo desde que fueron puestos. Comparados con niveles iniciales, hubo diferencias significativas en los metabolitos de los glucocorticoides fecales entre los pájaros control (6.1 ± 13.7 ng g−1) y con transmisores (102.3 ± 13.7 ng g−1) durante las primeras 24 hr despues de ponerlos. Aunque los pájaros con transmisores mostraron niveles elevados de glucocorticoides fecales, la respuesta aguda regresó a niveles iniciales en menos de 48 hr.

Movements of Translocated and Resident Three-toed Box Turtles

Abstract Translocation of terrestrial turtles occurs to mitigate habitat loss, increase population size or genetic diversity, and to establish new populations. The success of many translocation efforts often depends on social and economic factors, but ecological factors may also affect translocation success. We used radiotelemetry to evaluate Three-Toed Box Turtle (Terrapene carolina triunguis) movements before and after translocation from a continuously forested site to a highly fragmented site and made comparisons to resident turtles. The average distance moved between consecutive 28-h relocations (dist_move) pretranslocation versus posttranslocation depended on turtle origin. Turtles translocated from the continuously forested site had greater mean dist_move following translocation, whereas resident turtles at the fragmented site had similar dist_move in both periods. Translocated turtles traveled greater total distances, had greater net displacement, and greater home-range size than resident turtles. Additionally, translocated turtles had directed movements, whereas resident turtles did not. Homing behavior or directed movement toward continuous forest adjacent to the release site may account for the movement patterns observed. Future translocations should consider the landscape context of the release sites as well as the landscape context of the original capture location.

Wild turkey poult survival in southcentral Iowa

Poult survival is key to understanding annual change in wild turkey (Meleagris gallopavo) populations. Survival of eastern wild turkey poults (M. g. silvestris) 0-4 weeks posthatch was studied in southcentral Iowa during 1994-97. Survival estimates of poults were calculated based on biweekly flush counts and daily locations acquired via radiotelemetry. Poult survival averaged 0.52 ± 0.14% (x ± SE) for telemetry counts and 0.40 ± 0.15 for flush counts No within-vear or across-vear differences were detected between estimation techniques More than 72% (n - 32) of documented poult mortality occurred ≤14 days posthatch and mainmalian predation accounted for 92.9% of documented mortality. If mortality agents are not of concern e suggest biologists conduct 4-week flush counts to obtain poult survival estimates for use in population models and development of harvest recommendations.

Evaluation of transmitter attachment techniques on growth of wild turkey poults

We compared the effects on growth of backpack-mounted and surgically implanted radiotransmitters used as marking techniques in studies of wild turkey (Meleagris gallopavo) poult survival. We applied repeated-measures analysis of variance (ANOVA) and Bayesian analysis to evaluate the null hypothesis that marking technique did not affect growth. Growth in body mass was similar among treatment groups. We did, however, find differences in wing-growth rates among treatment groups. The control group had the highest wing-growth rate, the backpack group had the lowest growth rate, and the surgical implant group was intermediate. Latex backpack harnesses also caused physical developmental problems that would have negatively biased wild poult survival estimates in the field. Surgically implanted transmitters affected wing growth less than the backpack harnesses and are therefore recommended for attaching transmitters to wild turkey poults.

Effects of radiotransmitters on fecal glucocorticoid metabolite levels of three-toed box turtles in captivity

Abstract The increased use of radiotelemetry for studying movement, resource selection, and population demographics in reptiles necessitates closer examination of the assumption that radiotransmitter attachment does not bias study results. We determined the effects of radiotransmitter attachment on fecal glucocorticoid metabolite levels of wild three-toed box turtles (Terrapene carolina triunguis) in captivity. During May 2002 we captured 11 adult three-toed box turtles in central Missouri. We housed turtles in individual pens in a semi-natural outdoor setting. We radiotagged 6 turtles, and the remaining 5 turtles served as controls. We captured and handled all turtles similarly during treatments. We collected feces daily prior to attachment (14 June–05 July 2002), while transmitters were attached (06 July–02 August 2002), and after transmitters were removed (03 August–24 August 2002). We conducted a standard assay validation and found that the assay accurately and precisely quantified fecal glucocorticoid metabolites of box turtles. We did not find a significant effect of radiotransmitter attachment on fecal glucocorticoid metabolite levels of three-toed box turtles (F1,9 =0.404, P = 0.541). Fecal glucocorticoid metabolite levels of control and treatment turtles increased significantly during the study (F2,166 =7.874, P = 0.001), but there was no treatment:period interaction (F2, 166 = 0.856, P = 0.427). Additionally, we did not find a significant relationship between glucocorticoid metabolite levels and time in captivity (r2 = 0.01, F1,179 = 2.89, P = 0.091) or maximum daily temperature (r2<0.01, F1,179 = 0.301, P = 0.584). Our results suggested that radiotransmitter attachment did not significantly increase fecal glucocorticoid metabolite levels in adult three-toed box turtles; however, we conducted our study in captivity and sample sizes were small. Thus, more research is needed to assess potential effects of radiotransmitters on turtles in the wild. We believe this study is the first to validate the use of fecal glucocorticoid metabolite measures for reptiles, which might prove useful in other research studies.

Factors influencing wild turkey hen survival in southcentral Iowa

A decline in the population of eastern wild turkeys (Meleagris gallopavo silvestris) in southcentral Iowa necessitated more current estimates of population parameters. Survival of 126 eastern wild turkey hens in southcentral Iowa was investigated during 1993-96. Estimates of annual survival averaged 0.676 ± 0.048% (x ± SE) for adults and 0.713 ± 0.125 for subadults. Mammalian predators, primarily coyotes (Canis latrans) and red fox (Vulpes fulva) accounted for 64% of all documented mortality. Age-specific annual survival distributions differed within years (P < 0.03), but no difference was detected in survival between age classes across years (P = 0.49). Based on chronological dates, survival of adult hens differed among seasons across years (P = 0.03). However, seasonal survival was not different when estimates were based on hen behavior (P = 0.48) Risk of mortality for hens increased by 2.0% for every 100-m increase in dispersal distance, decreased by 2.0% for every 10-ha increase in home range size, and decreased by 3.5% for each 1.0% increase in proportion of home range in woody cover. Although the exact cause of the population decline remains unknown, we sugges it was more likely related to a decrease in production than changes in hen survival. Declining turkey populations would likely benefit more from management designed to increase reproduction rather than hen survival.

Resource Selection by Translocated Three-Toed Box Turtles in Missouri

Abstract Resource selection is a multi-staged process of behavioral responses to various resource cues or stimuli. Previous research suggests some aspects of resource selection may be inherent (i.e., genetic predisposition) or based on early experience and that individuals respond to certain resource cues but not to others. In other words, resource selection may be based on a template that specifies which cues to use in the resource-selection process and the appropriate response to those cues. We used resource utilization functions (RUFs) to examine the resource-selection template of translocated three-toed box turtles (Terrapene carolina triunguis; hereafter turtles) and made comparisons to resident turtles. Translocated turtles, previously residents of a predominantly forested landscape with low edge-density, used forest openings, forest edges, and southwest-facing slopes before and after translocation to a fragmented site containing resident turtles. In contrast, resident turtles used forested areas and northeast-facing slopes within a predominantly open landscape with high edge-density. Our comparison of resource selection by translocated and resident turtles revealed population-specific resource selection and consistency in selection following translocation, which reinforces the idea of a resource-selection template and suggests that in the short-term box turtles may not adapt their predisposed behavior to local conditions. Thus, translocated animals may evaluate and respond to resource cues as if they were at the original site. Lack of site fidelity may result from individuals seeking additional resources to match their resource-selection template. Successful translocation of turtles may require an assessment of resource selection prior to translocation and development of management strategies that mitigate turtle response to translocation.

Factors Affecting Home Range Size and Movements of Post-Fledging Grassland Birds

Abstract We describe post-fledging movements and evaluate the effects of local vegetation, temporal, and biological factors on home range size for two species of declining grassland birds in southwestern Missouri from 2002 to 2004. We obtained ≥30 detections for 74 individual juvenile Dickcissels (Spiza americana) and 64 juvenile Eastern Meadowlarks (Sturnella magna) during the post-fledging period. Juvenile Eastern Meadowlarks had a greater total number of days (6.7 ± 0.6) with large (>300 m) movements than juvenile Dickcissels (5.0 ± 0.5 days). Average Dickcissel home range size was larger and three times as variable in 2002 (77.0 ± 22 ha) compared to 2003 (31.4 ± 7.5 ha) and 2004 (34.9 ± 7.5 ha). There were year-specific effects of the variability in vegetation height on home range size of juvenile Dickcissels. Home range size was similar among years for juvenile Eastern Meadowlarks (2002, 109.4 ± 39.2 ha; 2003, 82.7 ± 29.4 ha; 2004, 70.7 ± 11.6 ha), but there was a year-specific effect of variability in grass cover on home range size of juvenile Eastern Meadowlarks. Local vegetation conditions are important factors affecting home range size and movements during the post-fledging period.