David G. Krementz

POSTFLEDGING SURVIVAL OF EUROPEAN STARLINGS

We tested the hypotheses that mass at fledging and fledge date within the breeding season affect postfledging survival in European Starlings (Sturnus vulgaris). Nest- lings were weighed on day 18 after hatch and tagged with individually identifiable patagial tags. Fledge date was recorded. Marked fledglings were resighted during weekly two-day intensive observation periods for >9 wk postfledging. Postfledging survival and sighting probabilities were estimated for each of four groups (early or late fledging by heavy or light fledging mass). Body mass was related to postfledging survival for birds that fledged early. Results were not clear-cut for relative fledge date, although there was weak evidence that this also influenced survival. Highest survival probability estimates occurred in the EAR- LY-HEAVY group while the lowest survival estimate occurred in the LATE-LIGHT group. Sighting probabilities differed significantly among groups, emphasizing the need to estimate

Fat scoring : sources of variability

Fat scoring is a widely used nondestructive method of assessing total body fat in birds. This method has not been rigorously investigated. We investigated interand intraobserver variability in scoring as well as the predictive ability of fat scoring using five species of passerines. Between-observer variation in scoring was variable and great at times. Observers did not consistently score species higher or lower relative to other observers nor did they always score birds with more total body fat higher. We found that within-observer variation was acceptable but was dependent on the species being scored. The precision of fat scoring was species-specific and for most species, fat scores accounted for less than 50% of the variation in true total body fat. Overall, we would describe fat scoring as a fairly precise method of indexing total body fat but with limited reliability among observers.

Simultaneous use of mark-recapture and radiotelemetry to estimate survival, movement, and capture rates

Biologists often estimate separate survival and movement rates from radiotelemetry and mark -recapture data from the same study population. We describe a method for combining these data types in a single model to obtain joint, potentially less biased estimates of survival and movement that use all available data. We furnish an example using wood thrushes (Hylocichla mustelina) captured at the Piedmont National Wildlife Refuge in central Georgia in 1996. The model structure allows estimation of survival and capture probabilities, as well as estimation of movements away from and into the study area. In addition, the mode structure provides many possibilities for hypothesis testing. Using the combined model structure, we estimated that weekly survival of wood thrushes was 0.989 ± 0.007 (±SE). Survival rates of banded and radiomarked individuals were not different (α[S radioed , S banded ] = log[S radioed /S banded ] = 0.0239, 95% CI = -0.0196 to 0.0486) Fidelity rates (weekly probability of remaining in a stratum) did not differ between geographic strata (ψ = 0.911 ± 0.020; α[ψ 11 ψ 22 ] = 0.0161, 95% CI = -0.0309 to 0.0631). and recapture rates (p = 0.097 ± 0.016) of banded and radiomarked individuals were not different (α[P radioed , P banded ] = 0.145, 95% CI = -0.510 to 0.800). Combining these data types in a common model resulted in more precise estimates of movement and recapture rates than separate estimation, but ability to detect stratum or mark-specific differences in parameters was weak. We conducted simulation trials to investigate the effects of varying study designs on parameter accuracy and statistical power to detect important differences. Parameter accuracy was high (relative bias [RBIAS] <2%) and confidence interval coverage close to nominal, except for survival estimates of banded birds for the off study area stratum, which were negatively biased (RBIAS -7 to -15%) when sample sizes were small (5-10 banded or radioed animals released per time interval). To provide adequate data for useful inference from this model, study designs should seek a minimum of 25 animals of each marking type observed (marked or observed via telemetry) in each time period and geographic stratum.

Effects of forest management on density, survival, and population growth of wood thrushes

Loss and alteration of breeding habitat have been proposed as causes of declines in several Neotropical migrant bird populations. We conducted a 4-year study to determine the effects of winter prescribed burning and forest thinning on breeding wood thrush (Hylocichla mustelina) populations at the Piedmont National Wildlife Refuge (PNWR) in Georgia. We estimated density, adult and juvenile survival rates, and apparent aunual survival using transect surveys, radiotelemetry, and mist netting. Burning and thinning did not cause lower densities (P = 0.25); wood thrush density ranged from 0.15 to 1.30 pairs/10 ha. No radiomarked male wood thrushes (n = 68) died during the 4 years, but female weekly survival was 0.981 ± 0.014 (SE) fo lemales (n = 63) and 0.976 ± 0.010 for juveniles (n = 38). Apparent annual adult survival was 0.579 (SE = 0.173) Thinning and prescribed burning did not reduce adult or juvenile survival during the breeding season or apparent annual adult survival. Annual population growth (λ) at PNWR was 1.00 (95% confidence interval [CI] = 0.32-1.63), and the considerable uncertainty in this prediction underscores the need for long-term monitoring to effectively manage Neotropical migrants, Population growth increased on experimental compartments after the burn and thin (95% CI before = 0.91-0.97, after = 0.98-1.05), while control compartment λ declined (before = 0.98-1.05, after = 0.87-0.92). We found no evidence that the current management regime at PNWB, designed to improve red-cockaded woodpecker (Picoides borealis) habitat, negatively affected wood thrushes.

A model to predict breeding-season productivity for multibrooded songbirds

Breeding-season productivity (the per capita number of offspring surviving to the end of the breeding season) is seldom estimated for multibrooded songbirds because of cost and logistical constraints. However, this parameter is critical for predictions of population growth rates and comparisons of seasonal productivity across geographic or temporal scales. We constructed a dynamic, stochastic, individual-based model of breeding-season productivity using demographic data from Wood Thrushes (Hylocichla mustelina) in central Georgia from 1993 to 1996. The model predicts breeding-season productivity as a function of adult survival, juvenile survival, nesting success, season length, renesting interval, and juvenile-care intervals. The model predicted that seasonal fecundity (number of fledglings produced) was 3.04, but only 2.04 juveniles per female survived to the end of the breeding season. Sensitivity analyses showed that differences in renesting interval, nesting success, fledglings per successful nest, and adult and juvenile survival caused variation in breeding-season productivity. Contrary to commonly held notions, season length and fledgling-care interval length did not cause variation in breeding-season productivity. This modeling exercise emphasizes the need for demographic data for songbird species, and we encourage biologists to use similar models to evaluate productivity in songbird populations.

WOOD THRUSH MOVEMENTS AND HABITAT USE: EFFECTS OF FOREST MANAGEMENT FOR RED-COCKADED WOODPECKERS

Abstract We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes (Hylocichla mustelina) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers (Picoides borealis), thinning and burning >30 year old loblolly pine (Pinus taeda) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (Ψ) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site (x̄ = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood–pine mixed habitat (P < 0.05) with moderate overstory cover (P < 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management.

SOURCES OF VARIATION IN WATERFOWL SURVIVAL RATES

Because of the need to manage hunted populations of waterfowl (Anatidae), biologists have studied many demographic traits of waterfowl by analyzing band recoveries. These analyses have produced the most extensive and best estimates of survival available for any group of birds. Using these data, we examined several factors that might explain variation among annual survival rates to explore large-scale patterns that might be useful in under- standing waterfowl population dynamics. We found that geography, body mass, and tribe (i.e. phylogeny) were important in explaining variation in average waterfowl survival rates. Received 22 April 1996, accepted 18 September 1996. ALTHOUGH MODERN METHODS for estimating survival rates have been available for 30 years (Cormack 1964, Jolly 1965, Seber 1965), these estimators have not been applied evenly among all groups of birds. Modern estimation proce- dures have been put to their fullest use in only one order, the Anseriformes. One reason for this emphasis is the need to understand the relationship between hunter harvest and

Model-based estimates of annual survival rate are preferable to observed maximum lifespan statistics for use in comparative life-history studies

Estimates of longevity are available for many animals, and are commonly used in comparative life-history analyses. We suggest that annual survival rate is a more appropriate life history parameter for most comparative life history analyses. Observed maximum lifespans estimate complicated functions of survival and sampling probabilities. Annual survival rate estimates derived from modern band-recovery statistical procedures are becoming available for a variety of organisms. We compiled annual survival rate estimates and observed maximum longevities derived from band recovery data for North American waterfowl. Observed maximum longevities were not correlated with the annual survival rate estimates and appear to be unstable over time. We recommend that observed maximum lifespans not be used in life history analyses.

CLEARCUT STAND SIZE AND SCRUB-SUCCESSIONAL BIRD ASSEMBLAGES

Abstract We investigated the effects of clearcut stand size on species richness, reproductive effort, and relative abundance of scrub-successional birds and the entire bird assemblage at the Savannah River Site in South Carolina. We used standardized mist-net grids to mark and recapture birds in clearcuts replanted with longleaf pine (Pinus palustris) in stands of 2 to 57 ha that were two to six years old. Species richness for the entire bird assemblage was not explained by stand size (P = 0.67), stand age (P = 0.95), or the interaction of these two variables (P = 0.90). Similarly, species richness of scrub-successional birds was not explained by stand size (P = 0.63), stand age (P = 0.55), or the interaction of stand size and stand age (P = 0.35). Regressing species richness on clearcut stand size, we found a significant negative relationship between these variables for the entire bird assemblage (P = 0.01) and for scrub-successional birds (P = 0.02). The ratio of juveniles to adults in mist-net samples varied by year (P = 0.04), but neither clearcut size (P = 0.23) nor the interaction of clearcut size and year (P = 0.25) was related to the ratio of juveniles to adults in the sample. We found no relationship between the frequency of capture of any category of birds and stand size (scrub-successional, P = 0.52; woodland, P = 0.77; combined sample, P = 0.55). Neither bird-species richness, reproductive effort, nor relative abundance differed across clearcut stand sizes. Clearcut stand size does not appear to be an important management variable if variation in species richness, reproductive effort, or relative abundance are objectives. We suggest that even-aged forestry is a useful tool for managing birds in the southeastern United States.

Distribution and Habitat Use of King Rails in the Illinois and Upper Mississippi River Valleys

Abstract The migratory population of the king rail (Rallus elegans) has declined dramatically during the past 40 years, emphasizing the need to identify habitat requirements of this species to help guide conservation efforts. To assess distribution and habitat use of king rails along the Illinois and Upper Mississippi valleys, USA, we conducted repeated call-broadcast surveys at 83 locations in 2006 and 114 locations in 2007 distributed among 21 study sites. We detected king rails at 12 survey locations in 2006 and 14 locations in 2007, illustrating the limited distribution of king rails in this region. We found king rails concentrated at Clarence Cannon National Wildlife Refuge, an adjacent private Wetlands Reserve program site, and B. K. Leach Conservation Area, which were located in the Mississippi River floodplain in northeast Missouri. Using Program PRESENCE, we estimated detection probabilities and built models to identify habitat covariates that were important in king rail site occupancy. Habitat covariates included percentage of cover by tall (>1 m) and short (≤1 m) emergent vegetation, percentage of cover of woody vegetation, and interspersion of water and vegetation (2007 only) within 50 m of the survey location. Detection probability was 0.43 (SE  =  0.12) in 2006 and 0.35 (SE  =  0.03) in 2007 and was influenced by observer identity and percentage of cover by tall herbaceous vegetation. Site occupancy was 0.11 (SE  =  0.04) in 2006 and 0.14 (SE  =  0.04) in 2007 and was negatively influenced most by percentage of cover by woody vegetation. In addition, we found that interspersion of vegetation and water was positively related to occupancy in 2007. Thus, nesting king rails used wetlands that were characterized by high water–vegetation interspersion and little or no cover by woody vegetation. Our results suggest that biologists can improve king rail habitat by implementing management techniques that reduce woody cover and increase vegetation–water interspersion in wetlands.