Mark R. Ryan

Conservation Reserve Program: Source or Sink Habitat for Grassland Birds in Missouri?

The Conservation Reserve Program (CRP) has been eredited with contributing substantially to the conservation of grassland birds. Although many species have nested in grasslands established under the CRP, little evidence of positive effect on populations has been reported. We measured reproductive rates and estimated fecundity of 7 grassland bird species in CRP fields in northern Missouri and compared those rates to estimates of fecundity needed to maintain stable populations (λ = 1). Under conservative assumptions of survival, CRP fields seemingly were source habitats (fecundity exceeded levels necessary for λ = 1) for grasshopper sparrows (Ammodramus savannarum) and field sparrows (Spizella pusilla) in at least 2 of 3 years (1993: P = 0.02, 1995: P < 0.001) and pooled over 3 years (Ps < 0.001). Although evidence was less compelling, CRP fields were likely source habitat for eastern meadowlarks (Sturnella magna) and American goldfinches (Carduelis tristis). For American goldfinches, fecundity was greater than that necessary for λ = 1 in 1995 (P < 0.001), and pooled over 3 years (P < 0.001). Our pooled estimate of fecundity was greater than necessary for λ = 1 for eastern meadowlarks (Ps < 0.001), but only under a liberal assumption of survival in 2 of 3 years (1993: P = 0.001; 1995: P = 0.088). Fecundity of common yellowthroats (Geothlypis trichas) varied substantially; therefore, source-sink status alternated among years, although the pooled estimate of fecundity was less than required for λ = 1 (P < 0.001). Dickcissel (Spiza americano) fecundity was consistently less than necessary for λ = 1 (conservative survival assumption: all Ps < 0.001; liberal survival assumption: 1994 P - 0.008. pooled P = 0.014). For red-winged blackbirds (Agelaius phoeniceus), CRP fields were consistently a sink habitat (all Ps < 0.001). Based on our evidence, the CRP likely has contributed to the conservation of grasshopper sparrows, field sparrows. and eastern meadowlarks. Although large numbers of dickcissels and red-winged black-birds nested in CRP fields, there is little evidence that the CRP has contributed to populations of those species.

Grassland Bird Conservation: CP1 vs. CP2 Plantings in Conservation Reserve Program Fields in Missouri

Abstract To determine the relative value of different Conservation Reserve Program (CRP) plantings for breeding grassland and winter birds we measured vegetation structure, avian abundance and reproductive success, and estimated fecundity during 1993–1995 on CP1 (cool-season grass) and CP2 (warm-season grass) plantings in 16 fields in northern Missouri. CP1 fields had been planted to cool-season grasses or cool-season grass-legume mixtures and CP2 fields had been seeded with switchgrass (Panicum virgatum). Species richness, abundance and nesting success of grassland birds during the breeding season and total bird use in the winter did not differ between CPs. During the breeding season CP1 fields had higher abundances of grasshopper sparrow (Ammodramus savannarum), eastern meadowlark (Sturnella magna), Henslows sparrow (Ammodramus henslowii) and American goldfinches (Carduelis tristis), whereas common yellowthroats (Geothlypis trichas) were more abundant in CP2 fields. Fecundity of dickcissels (Spiza americana) and nesting success and fecundity of red-winged blackbirds (Agelaius phoeniceus) were higher on CP2 than on CP1 habitat, but both CPs were likely sinks (λ < 1) for these species. Both CPs were likely source (λ > 1) habitat for grasshopper sparrows, whereas only CP1 habitat was likely a source for eastern meadowlarks and American goldfinches. In winter American goldfinches were more abundant in CP1 fields than CP2 fields. The shorter, more diverse, cool-season grass fields were equal or better habitat than taller, more vertically dense, switchgrass-dominated fields for grassland birds, including several species of high conservation concern. Single-species plantings of warm- or cool-season grasses should be avoided to increase the potential wildlife benefits of CRP and other grassland habitats.

Reproductive strategies, success, and mating systems of northern bobwhite in Missouri

To better understand the reproductive mechanisms that enable northern bobwhite (Colinus virginianus) to recover from high annual mortality, we studied the reproductive strategies, success, and mating systems of 321 radio-marked bobwhite in northern Missouri during 1990-92. Seventy-four female and 43 male bobwhite incubated 159 nests. Females exhibited apparent monogamy during 60% of nesting attempts and apparent polyandry during 40%. Over the entire nesting season, 71% of females were polyandrous. Of those birds alive 15 April (n = 112 F, n = 148 M), 40.2% of females and 13.5% of males successfully hatched ≥1 nest. Seventy-four percent of females (n = 42) and 26% of males (n = 50) surviving until 1 September successfully hatched ≥1 nest. Nesting females that survived the nesting period incubated a mean of 1.8 nests (SE = 0.13), and males incubated 1.0 nests (SE = 0.04). Of those birds that failed on an initial nesting attempt, 57.9% of females (n = 38) and 2 of 23 males incubated ≥1 renest. Of those females that were successful on their initial nesting attempt, 25.7% attempted second nests. Female first nests represented 45.9%, female renests 20.1%, female double-clutch attempts 5.7%, and male-incubated nests 28.3% of all nests located. Nest survival was 43.7% (SE = 3.9). The reproductive system of northern bobwhite enables recovery from low annual survival or periodic catastrophic declines and may be an adaptation to fluctuating resources in ephemeral, dynamic habitats.

Survival and cause-specific mortality of northern bobwhite in Missouri

Efforts to understand fluctuations in northern bobwhite (Colinus virginianus) abundance illustrate inadequate knowledge of demographic processes. Therefore, we estimated seasonal survival, annual survival, and cause-specific mortality of 1,001 radio-marked bobwhite in northern Missouri. Annual survival was 5.3 ± O.5% and did not differ between ages (P = 0.33) or sexes (P = 0.48). Fall-spring survival (15.9 ± 0.8%) was less than spring-fall survival (33.2 ± 2.7%, P < 0.001). Females had lower fall-spring survival (13.7 ± 1.1%) than males (17.6 ± 1.1%, P = 0.02). Male-biased sex ratios likely result from differential fall and winter survival. Avian (28.7%) and mammalian (25.7%) predators were primary natural mortality agents. Hunter-retrieved (22.9%) and -unretrieved (5.3%) kill resulted in 28.2% harvest-related mortality. During springfall, males experienced higher avian mortality (26.5%) than females (20.0%) (P = 0.09). Greater vulnerability of males to avian predators may represent a cost of displaying. Each incubation and brood-rearing attempt reduced survival by 16% when compared with nonreproductively active birds during a similar period. Bobwhites must be highly productive to replace annual population losses

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.

Population viability of piping plovers: Effects of predator exclusion

The Great Plains population of piping plovers (Charadrius melodus) is listed as threatened or endangered and continues to decline. The effects of recently initiated management to exclude predators and a new, higher estimate of adult survival on the extinction risk of this population have not been evaluated. We estimated fledging success rates and revised a stochastic simulation model of plover demography to simulate population growth scenarios. Fledging rates without predator exclusion were 0.89 (SE = 0.10) fledglings/pair at alkaline wetlands and 0.73 (SE = 0.21) fledglings/pair at rivers and reservoirs. Predator exclusion increased local fledging rates to 1.15-2.25 fledglings/pair. Simulated population growth under current levels of management was -4.3%/year, which was higher than indicated by previous models but lower than indicated by international censuses in 1991 and 1996. A population-wide fledging rate of 1.10 fledglings/pair was needed to stabilize simulated populations. Our results indicate that the Great Plains population of piping plovers can be stabilized or increased if management activities to improve reproductive success are increased.

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.

PIPING PLOVER SURVIVAL IN THE GREAT PLAINS: AN UPDATED ANALYSIS

Abstract Population viability analyses for Piping Plovers (Charadrius melodus) are highly sensitive to survival estimates, especially those of adults. Thus, the discrepancy between the previous adult survival estimate for the Great Plains Piping Plover population (0.664, SE = 0.057) and estimates from other regions and closely related species prompted us to re-examine banding data for Great Plains plovers. We used published data plus three additional years of band resightings, data from banded juveniles, and a new modeling approach to estimate local annual survival rates of adults and immatures for a breeding site in central North Dakota in 1984–1994. Mean adult survival was 0.737 (SE = 0.092), and the temporal variance was 0.040–0.045. Immature survival was 0.318 (SE = 0.075), but true immature survival is probably higher, mostly due to unknown but likely high dispersal rates. Based on our revised survival estimate for adult Piping Plovers and projections from published plover population models, it is likely that the feasibility of recovering the Great Plains population is greater than previously thought.

Avian Abundance in CRP and Crop Fields during Winter in the Midwest

Abstract We compared the abundance and species composition of birds in Conservation Reserve Program (CRP) fields with the same aspects in row-crop fields during the winter (January and February) over several years (1992–1995) for six midwestern states (Indiana, Iowa, Kansas, Michigan, Missouri and Nebraska). Field techniques were standardized in all states. CRP fields consisted of either permanent introduced grasses and legumes (CP1) or permanent native grasses (CP2), and the plant species seeded in CRP fields differed within and among states. Vegetation characteristics of CRP fields varied considerably from state to state, but vertical density and total canopy cover (primarily grasses) were particularly high in Nebraska. Mean annual total bird abundance ranged from 0.1 to 5.1 birds per km of transect in CRP fields and from 0.1 to 24.2 in row-crop fields. The total number of bird species recorded in CRP fields in the six states ranged from 6 to 32; the range for row-crop fields was 8 to 18. The most abundant species in CRP fields differed among states but included the ring-necked pheasant, American tree sparrow, northern bobwhite, dark-eyed junco and American goldfinch. The most abundant species in row-crop fields included the horned lark, American tree sparrow, European starling, mourning dove, lapland longspur, meadowlarks and Canada goose. Some of the most abundant bird species wintering on CRP fields have been undergoing long-term population declines, thus this program has the potential to mitigate population losses.

Predicting greater prairie-chicken nest success from vegetation and landscape characteristics

To aid management of prairie habitat for nesting greater-prairie chickens (Tympanuchus cupido pinnatus), we tested whether vegetation and landscape variables could be used to predict prairie-chicken nest success. We monitored 60 nests during the 1990-92 breeding seasons in southwestern Missouri. Nest success ranged from 28 to 40% over 3 years (x = 35%). We identified 22-variable models (logistic regression) incorporating litter (horizontal, residual) and woody cover (P 0.5). Nest sites with litter cover >25% had a failure rate twice that of nests with 5% was present at nests (P = 0.01), when forb cover was ≤5% (P = 0.009), or when grass cover was ≤25% (P = 0.02). We suggest that managers can use litter accumulation of >25% as a cue to initiate management action such as burning, grazing, or haying.