Golden-cheeked Warbler Research Articles

Fire in a sub-humid woodland: The balance of carbon sequestration and habitat conservation

Public lands are often tasked with ecosystem restoration that may include fire as a management tool in order to foster the return of ecosystem composition, structure, or function to a previous state. In some ecosystems, such as woodlands, the role of fire is poorly understood because mixed-fire regimes complicate assessment of landscape level fire return intervals and successional pathways. Management of these public woodlands may be difficult due to the need to accomplish multiple objectives such as carbon (C) sequestration and wildlife conservation on properties with marginal productivity. To assess the role of fire in affecting various ecological processes and offer information for future wildland management decision-making, we measured C storage, vegetation composition, and habitat suitability for an endangered bird species (golden-cheeked warbler, Dendroica chrysoparia) in juniper-oak woodlands with documented past surface fires within Balcones Canyonlands National Wildlife Refuge. We found significantly different total aboveground biomass C with average values of 5.25, 6.86, and 9.18kgm−2 of C for 60 plots grouped into recent (<40year), old (⩾40year), and no fire treatments, respectively. Interpretation of fire for each plot was based on fire scar data derived from a previous tree-ring study for the refuge. We found fire significantly reduced site C primarily due to reduced tree density. We also found increased oak recruitment associated with fires that occurred in low summer precipitation years. Calculated habitat suitability index values for the golden-cheeked warbler did not significantly differ between groups. However, fire may have a dual effect on habitat suitability. While catastrophic wildfire can damage potential habitat and significantly reduce regional carbon storage, our study showed that moderate intensity fires in dense young juniper stands promotes tree species diversity, favorable for future habitat formation. We conclude that fire as a management focus, including use of prescribed burning and fuel treatments to reduce wildfire risk, may be implemented on a single conservation property to achieve multiple expected outcomes. However, this requires detailed ecological information regarding woody species composition and population structure to help assess legacy conditions that influence the interpretation of present woodland conditions and future projections given restoration efforts.

Chapter 8: Experimental determination of the response of Golden-cheeked Warblers (Setophaga chrysoparia) to road construction noise

Abstract Noise pollution can mask or distort bird songs, which can inhibit mating success, predator detection, and parental response to begging calls. We examined the impact of road construction noise on territory selection, reproductive success, and behavior of the federally endangered Golden-cheeked Warbler (Setophaga chrysoparia). To examine habituation and territory placement, we (1) used construction-noise playback to individual Golden-cheeked Warblers and evaluated occurrence of behavioral response as a function of distance from the roadway, and (2) established broadcast units that simulated construction noise to determine effects on territory selection. Among 88 surveys, six birds responded to construction-noise playback; all birds that responded were located ≥140 m from the road. We established three broadcast units per season in 2008 and 2009 to test for habituation. In each year, we placed broadcast units on the edges of randomly chosen territories identified during the previous field season. We...

Conspecific cues and breeding habitat selection in an endangered woodland warbler

1. Research on habitat selection has focused on the role of vegetative and geologic characteristics or antagonistic behavioural interactions. 2. Conspecifics can confer information about habitat quality and provide positive density-dependent effects, suggesting habitat selection in response to the presence of conspecifics can be an adaptive strategy. 3. We conducted a manipulative field experiment investigating use of conspecific location cues for habitat selection and consequent reproductive outcomes for the endangered golden-cheeked warbler (Setophaga chrysoparia). We investigated the response in woodlands across a range of habitat canopy cover conditions typically considered suitable to unsuitable and using vocal cues presented during two time periods: pre-settlement and post-breeding. 4. Warblers showed a strong response to both pre-settlement and post-breeding conspecific cues. Territory density was greater than four times higher in treatment sample units than controls. The magnitude of response was higher for cues presented during the pre-settlement period. Positive response to conspecific cues was consistent even in previously unoccupied areas with low canopy cover typically considered unsuitable, resulting in aggregations of warblers in areas generally not considered potential habitat. 5. Pairing and reproductive success of males was not correlated with canopy cover, as commonly thought. Pairing success and fledging success increased with increasing territory density suggesting that conspecific density may be more important for habitat selection decisions than the canopy cover conditions typically thought to be most important. These results suggest the range of habitat within which birds can perform successfully may be greater than is typically observed. 6. Our results suggest the territory selection process may not be substantially influenced by competition in some systems. Settlement in response to conspecific cues produced aggregations within larger areas of similar vegetative characteristics. Understanding what cues drive habitat selection decisions and whether these cues are correlated with habitat quality is critical for conserving fitness-enhancing habitats, avoiding creation of ecological traps, generating accurate predictions of species distributions and understanding how occupancy relates to habitat suitability.

Estimating breeding season abundance of golden‐cheeked warblers in Texas, USA

AbstractPopulation abundance estimates using predictive models are important for describing habitat use and responses to population‐level impacts, evaluating conservation status of a species, and for establishing monitoring programs. The golden‐cheeked warbler (Setophaga chrysoparia) is a neotropical migratory bird that was listed as federally endangered in 1990 because of threats related to loss and fragmentation of its woodland habitat. Since listing, abundance estimates for the species have mainly relied on localized population studies on public lands and qualitative‐based methods. Our goal was to estimate breeding population size of male warblers using a predictive model based on metrics for patches of woodland habitat throughout the species' breeding range. We first conducted occupancy surveys to determine range‐wide distribution. We then conducted standard point‐count surveys on a subset of the initial sampling locations to estimate density of males. Mean observed patch‐specific density was 0.23 males/ha (95% CI = 0.197–0.252, n = 301). We modeled the relationship between patch‐specific density of males and woodland patch characteristics (size and landscape composition) and predicted patch occupancy. The probability of patch occupancy, derived from a model that used patch size and landscape composition as predictor variables while addressing effects of spatial relatedness, best predicted patch‐specific density. We predicted patch‐specific densities as a function of occupancy probability and estimated abundance of male warblers across 63,616 woodland patches accounting for 1.678 million ha of potential warbler habitat. Using a Monte Carlo simulation, our approach yielded a range‐wide male warbler population estimate of 263,339 (95% CI: 223,927–302,620). Our results provide the first abundance estimate using habitat and count data from a sampling design focused on range‐wide inference. Managers can use the resulting model as a tool to support conservation planning and guide recovery efforts. © 2012 The Wildlife Society.

Utilization of a species occupancy model for management and conservation

AbstractConserving habitat is increasingly challenging as human populations grow. Remote‐sensing technology has provided a means to delineate species' habitat on large spatial scales. However, by combining habitat delineations with predictions of species' occurrence, habitat models can provide additional utility applications for conservation by allowing us to forecast how changing environmental and landscape conditions affect species' occurrence and distribution. We demonstrate how a spatially explicit habitat occupancy model for the golden‐cheeked warbler (Setophaga chrysoparia) can be used as an impact assessment and conservation planning tool. We used predictions of patch‐level occupancy rates and created several scenarios that simulated the removal or protection of warbler habitats. Resulting changes to habitat structure and availability were used to assess the resulting impacts of removal or protection on the occurrence probability for remaining habitat patches. By recalculating occupancy based on changes to habitat, our approach provides the ability to assess and compare impacts of location and orientation of development so that the least harmful option relative to predicted occurrence can be chosen. Potential applications of our modeling approach are many because our methods provide a useful tool for identifying potential impacts and assisting with mitigation efforts focused on the conservation and management of a species. © 2012 The Wildlife Society.

Canopy characteristics affect reproductive success of golden‐cheeked warblers

AbstractThe golden‐cheeked warbler (Setophaga chrysoparia), listed by the U.S. Fish and Wildlife Service as endangered in 1990 due primarily to habitat loss and fragmentation, is a Neotropical migrant songbird that breeds exclusively in mature juniper–oak (Juniperus–Quercus) woodlands in central Texas, USA. Previous studies suggested suitable breeding habitat consists of &gt;35% canopy closure (with 50–70% cover optimal), and ≥10% oak composition. However, little is known about this species' habitat relationships at the southwestern edge of its breeding range. Therefore, within this portion of the species' breeding range, we investigated influences of canopy closure and tree species composition on pairing and reproductive success of golden‐cheeked warblers during 2009 and 2010. We used remote sensing and ground sampling to acquire variables to describe habitat characteristics, and we estimated pairing for breeding and reproductive success by golden‐cheeked warblers. We found successfully breeding pairs in areas with &gt;20% canopy cover, 35% juniper composition, and only 3% oak composition. A logistic model for pairing success retained juniper, oak, and the interaction between these 2 variables, and the model for reproductive success retained juniper, canopy closure, study area, and the interaction between canopy closure and study area. Our results expand our knowledge of habitat conditions that warblers use for breeding, thus expanding the range of habitat management options available for this species during breeding season. © 2012 The Wildlife Society.

Reliability of occupancy and binomial mixture models for estimating abundance of Golden-cheeked Warblers (Setophaga chrysoparia)

ABSTRACT. Reliable estimates of population parameters derived from survey methods are essential for decision making in management of endangered species. We evaluated whether point-count surveys used in conjunction with occupancy and binomial mixture models (BMMs) constituted a reliable approach for monitoring the federally endangered Golden-cheeked Warbler (Setophaga chrysoparia) on a preserve in central Texas. Occupancy and abundance were estimated using point-count surveys conducted on each of five 113-ha detection grids in 2008 and seven grids in 2009. Single-season occupancy models and BMMs were used to estimate occupancy and abundance, respectively. Occupancy estimates per grid ranged from 0.48 to 1.0 in 2008 and from 0.52 to 1.0 in 2009. Estimates of abundance were compared with territory densities independently estimated using spot mapping, the standard by which all other avian survey methods are often compared. Abundance estimates produced by BMMs were significantly higher than territory density e...

Quantifying the importance of patch-specific changes in habitat to metapopulation viability of an endangered songbird

A growing number of programs seek to facilitate species conservation using incentive-based mechanisms. Recently, a market-based incentive program for the federally endangered Golden-cheeked Warbler (Dendroica chrysoparia) was implemented on a trial basis at Fort Hood, an Army training post in Texas, USA. Under this program, recovery credits accumulated by Fort Hood through contracts with private landowners are used to offset unintentional loss of breeding habitat of Golden-cheeked Warblers within the installation. Critical to successful implementation of such programs is the ability to value, in terms of changes to overall species viability, both habitat loss and habitat restoration or protection. In this study, we sought to answer two fundamental questions: Given the same amount of change in breeding habitat, does the change in some patches have a greater effect on metapopulation persistence than others? And if so, can characteristics of a patch (e.g., size or spatial location) be used to predict how the metapopulation will respond to these changes? To answer these questions, we describe an approach for using sensitivity analysis of a metapopulation projection model to predict how changes to specific habitat patches would affect species viability. We used a stochastic, discrete-time projection model based on stage-specific estimates of survival and fecundity, as well as various assumptions about dispersal among populations. To assess a particular patch's leverage, we quantified how much metapopulation viability was expected to change in response to changing the size of that patch. We then related original patch size and distance from the largest patch to each patch's leverage to determine if general patch characteristics could be used to develop guidelines for valuing changes to patches within a metapopulation. We found that both the characteristic that best predicted patch leverage and the magnitude of the relationship changed under different model scenarios. Thus, we were unable to find a consistent set of relationships, and therefore we emphasize the dangers in relying on general guidelines to assess patch value. Instead, we provide an approach that can be used to quantitatively evaluate patch value and identify critical needs for future research.

Establishing quantitative habitat targets for a ‘Critically Endangered’ Neotropical migrant (Golden-cheeked WarblerDendroica chrysoparia) during the non-breeding season

SummaryThe Golden-cheeked WarblerDendroica chrysopariais a federally endangered Neotropical migrant that inhabits montane pine-oak forests in Mexico and northern Central America during the non-breeding season. Although it is known that Golden-cheeked Warblers are closely associated with ‘encino’ oaks (evergreen or holm oak) such asQuercus sapotifolia,Q. elipticaandQ. elongata,which have shiny, narrow, elliptical, or oblong leaves, quantitative habitat targets are useful for effectively incorporating this information into conservation planning and forest management practices. We analysed data on wintering Golden-cheeked Warblers collected during the non-breeding season in Honduras from 1996 to 1998 to identify quantitative targets for habitat conditions for this species. Data on warbler abundance were collected using line transect surveys located in montane pine-oak forests in a stratified-random fashion. Habitat data were collected at five 0.04 ha plots on these same transects and the averaged values used as predictors of Golden-cheeked Warbler abundance. We found that Golden-cheeked Warblers were strongly associated with the basal area ofencinooaks and density of ‘roble’ oaks, such asQ. segoviensis,Q. purulhanaandQ. rugosa, which have large, lobed leaves. Density of Golden-cheeked Warblers peaked at ≈ 5.6 m2ha–1basal area ofencinoand ≈7robleoaks ha–1. These values can be used to identify quantitative habitat targets that can be directly incorporated into forest management practices to ensure that these activities maintain habitat conditions necessary for their use by Golden-cheeked Warblers.

Predicting patch occupancy in fragmented landscapes at the rangewide scale for an endangered species: an example of an American warbler.

AIM: Our objective was to identify the distribution of the endangered golden-cheeked warbler (Setophaga chrysoparia) in fragmented oak-juniper woodlands by applying a geoadditive semiparametric occupancy model to better assist decision-makers in identifying suitable habitat across the species breeding range on which conservation or mitigation activities can be focused and thus prioritize management and conservation planning. LOCATION: Texas, USA. METHODS: We used repeated double-observer detection/non-detection surveys of randomly selected (n = 287) patches of potential habitat to evaluate warbler patch-scale presence across the species breeding range. We used a geoadditive semiparametric occupancy model with remotely sensed habitat metrics (patch size and landscape composition) to predict patch-scale occupancy of golden-cheeked warblers in the fragmented oak-juniper woodlands of central Texas, USA. RESULTS: Our spatially explicit model indicated that golden-cheeked warbler patch occupancy declined from south to north within the breeding range concomitant with reductions in the availability of large habitat patches. We found that 59% of woodland patches, primarily in the northern and central portions of the warbler's range, were predicted to have occupancy probabilities ≤0.10 with only 3% of patches predicted to have occupancy probabilities >0.90. Our model exhibited high prediction accuracy (area under curve = 0.91) when validated using independently collected warbler occurrence data. MAIN CONCLUSIONS: We have identified a distinct spatial occurrence gradient for golden-cheeked warblers as well as a relationship between two measurable landscape characteristics. Because habitat-occupancy relationships were key drivers of our model, our results can be used to identify potential areas where conservation actions supporting habitat mitigation can occur and identify areas where conservation of future potential habitat is possible. Additionally, our results can be used to focus resources on maintenance and creation of patches that are more likely to harbour viable local warbler populations.

A field test of the distance sampling method using Golden-cheeked Warblers

ABSTRACT Criteria for delisting Golden-cheeked Warblers (Dendroica chrysoparia) include protection of sufficient breeding habitat to ensure the continued existence of 1000 to 3000 singing males in each of eight recovery regions for ≥10 consecutive years. Hence, accurate abundance estimation is an integral component in the recovery of this species. I conducted a field test to determine if the distance sampling method provided unbiased abundance estimates for Golden-cheeked Warblers and develop recommendations to improve the accuracy of estimates by minimizing the effects of violating this method's assumptions. To determine if observers could satisfy the assumptions that birds are detected at the point with certainty and at their initial locations, I compared point-transect sampling estimates from 2-, 3-, 4-, and 5-min time intervals to actual abundance determined by intensive territory monitoring. Point-transect abundance estimates were 15%, 29%, 43%, and 59% greater than actual abundance (N= 156) for the 2-, 3-, 4-, and 5-min intervals, respectively. Point-transect sampling produced unbiased estimates of Golden-cheeked Warbler abundance when counts were limited to 2 min (N= 154–207). Abundance estimates derived from point-transect sampling were likely greater than actual abundance because observers did not satisfy the assumption that birds were detected at their initial locations due to the frequent movements and large territory sizes of male Golden-cheeked Warblers. To minimize the effect of movement on abundance estimates, I recommend limiting counts of singing males to 2-min per point. Counts for other species in similar habitats with similar behavior and movement patterns also should be limited to 2 min when unbiased estimates are important and conducting field tests of the point-transect distance sampling method is not possible. Criterios para remover de la lista a D. chrysoparia incluye protección de suficiente hábitat de reproducción para asegurar la existencia continua de 1000 a 3000 machos cantando en cada una de las ochos regiones de recuperación por más de 10 años consecutivos. Por lo tanto, medidas precisas de estimación de la abundancia son un componente integral para la recuperación de esta especie. Conduje una prueba de campo para determinar si el método de muestreo de distancia proporciona una estimación no segada de la abundancia de D. chrysoparia y desarrollar recomendaciones para mejorar la precisión de los estimados a través de la disminución de los efectos que violan los supuestos de este método. Para determinar si los observadores pueden satisfacer los supuestos que las aves son detectadas en el punto con certeza y en su localización inicial, compare muestras de transectos de punto de muestreo con intervalos de tiempo de 2-, 3-, 4-, y 5-min a muestras de abundancias reales determinadas a través de un intenso monitoreo de territorios. Las estimaciones de abundancia de los transecto de punto fueron 15%, 29%, 42% y 59% más grandes que la abundancia real (N= 156) para los intervalos de 2-, 3-, 4-, y 5-min, respectivamente. Muestreos de transecto de punto produjeron estimativos de la abundancia de D. chrysoparia no sesgados cuando los conteo se limitaron a 2 min (N= 154–207). Estimativos de abundancia provenientes de transecto de puntos fueron probablemente mayores que abundancias reales porque los observadores no satisficieron el supuesto que las aves fueron detectadas en la localización inicial debido a los frecuentes movimientos y largos territorios de los machos de D. chrysoparia. Para reducir el efecto de los movimientos en los estimativos de abundancia, recomiendo limitar los conteos de machos cantando a 2 min por punto. Conteos de otras especies en habita similares con comportamientos similares y patrones de movimiento también deben limitarse a 2 min, cuando los estimativos no sesgados son importantes y cuando conducir pruebas de campo de los muestreos de distancia de transectos de punto no es posible.

Crumbling diversity: comparison of historical archived and contemporary natural populations indicate reduced genetic diversity and increasing genetic differentiation in the golden-cheeked warbler

Genetic viability of threatened and endangered species is of increasing concern with habitat loss and fragmentation. Valuable assessments of the genetic status of endangered species are difficult in most cases, where only single sample estimates are available. Using historical and contemporary samples, we assessed the impact of both historical and recent demographic changes on population genetics of the endangered golden-cheeked warbler, (Dendroica chrysoparia). Our study documents a steep decline in genetic diversity in an endangered species over a 100-year period, along with concurrent increase in genetic differentiation, and low contemporary effective sizes for all the populations we evaluated. While adding to the growing body of literature that describes the genetic impacts of habitat fragmentation, our study may also serve as an informative guide to future management of endangered species. Our study underlines the importance of long term population genetic monitoring in understanding the full extent of genetic changes in endangered species.

Point-Based Mark-Recapture Distance Sampling

Avian surveys using point sampling for abundance estimation have either focused on distance sampling or more commonly mark-recapture to correct for detection bias. Combining mark-recapture and distance sampling (MRDS) has become an effective tool for line transects, but it has been largely ignored in point sampling literature. We describe MRDS and show that the previously published methods for point sampling are special cases. Using simulated data and golden-cheeked warbler (Dendroica chrysoparia) survey data from Texas, we demonstrate large differences in abundance estimates resulting from different independence assumptions. Data and code are provided in supplementary materials.

Effects of road construction noise on the endangered golden‐cheeked warbler

AbstractNoise pollution can mask or distort bird songs, which can inhibit mating success, predator detection, and parental response to begging calls. Using an impact assessment design, we examined the potential influence of road construction and road noise on territory placement, reproductive success, and density of the federally endangered golden‐cheeked warbler (Dendroica chrysoparia) at 3 sites: adjacent to road construction, adjacent to road‐noise only, and a control with no noise or activity. Although not statistically significant, reproductive success was about 20% higher and stable at road‐noise‐only sites relative to other treatments. Warbler density was similar among sites (construction = 0.305 birds/ha; road‐noise = 0.357 birds/ha; and control = 0.328 birds/ha). Average distance from road was similar for territories with paired adults (road‐noise = 291 m [SE = 26], construction = 263 m [SE = 19]) and those with successful pairs (road‐noise = 292 m [SE = 27]), construction = 243 m [SE = 21]). Overall noise levels were low: ambient noise was similar in the construction and road‐noise‐only sites ($\overline {X} $ = 32 dB) and showed little auditory difference from the control ($\overline {X} $ = 28 dB). Our results indicate that construction activities and road‐noise did not appear to impact territory placement, reproductive success, or local densities of golden‐cheeked warblers under the treatment regime we studied. © 2011 The Wildlife Society.

Variation of Type B Song in the Endangered Golden-Cheeked Warbler (Dendroica chrysoparia)

The Golden-cheeked Warbler (Dendroica chrysoparia), a member of the Parulidae, uses a two-category song system referred to as Type A and Type B. However, songs recorded from adult males in Bexar County, Texas, USA, did not resemble the typical A or B songs reported for this species. We report an analysis of these atypical songs from six adult males. Quantitative features of the measured songs and syllable structure suggest this atypical song is more comparable to a B song than an A song with some modifications. The atypical song has dropped a terminal syllable of the known B song, and selectively modified one of the syllables to include frequency modulations (up and down slurs). Further, the known B song was not heard in the investigated sites. We conclude the atypical song is a variant of the B song.

Mountain Biking Trail Use Affects Reproductive Success of Nesting Golden-Cheeked Warblers

We evaluated foraging and nesting behavior, territory size, and nest success of Golden-cheeked Warblers (Dendroica chrysoparia), a federally endangered songbird, relative to mountain biking trail use. We conducted our study at two mountain biking sites and two control sites at Fort Hood Military Base and in Austin, Texas, in spring 2002 and 2003. Territories of male Golden-cheeked Warblers in biking sites (2.2 ha) were >1.5 times as large as those in non-biking sites (1.4 ha). Mayfield nest success in biking sites (n = 33) was 35% compared to 70% in non-biking sites (n = 22). Nest abandonment was three times greater in biking areas (15%) than non-biking areas (5%). Seven nests were depredated in biking sites, but only two nests were depredated in non-biking sites. Texas rat snakes (Elaphe obsoleta) were the most frequent nest predator at biking sites, accounting for 71% of the predations. We conducted behavioral observations of male Golden-cheeked Warblers in biking (n = 139) and non-biking (n = 204) sites. Males spent similar amounts of time in diurnal behaviors in biking and non-biking sites. We used video-camera systems to record female nesting behaviors at 17 nests in biking sites and 15 nests in non-biking sites. Nesting behaviors of females did not differ between biking and non-biking sites. The cumulative effect of disturbance from mountain biking trail use on Golden-cheeked Warbler foraging and nesting behavior appears to be minimal, but fragmentation and alteration of habitat by mountain biking trails may reduce quality of nesting habitat for Golden-cheeked Warblers.

Characterization of golden-cheeked warbler Dendroica chrysoparia habitat at Fort Hood, Texas, USA

The golden-cheeked warbler Dendroica chrysoparia is a federally endangered, neotropical-nearctic migrant songbird that breeds in central Texas, USA, and prefers mature, closed canopy oak-Ashe juniper woodlands for nesting and foraging. Fort Hood is an 87 890 ha military reservation located in central Texas in Bell and Coryell Counties on the eastern edge of the Edwards Plateau ecoregion. We surveyed for golden-cheeked warblers and measured habitat variables at 95 separate locations in a 56.6 km 2 research area that supports a golden-cheeked warbler breeding population. We detected golden-cheeked warblers on 34 of 95 (36%) point count locations. Principal component analysis was used to reduce the 27 habitat variables to a set of uncorrelated variables. This analysis resulted in the identification of 4 principal components that accounted for 52% of the variance. Logistic regression identified one principal component (ratio of Ashe juniper to other woody species) that was strongly related to golden-cheeked warbler occurrence. Our data indicate that a 4:1 ratio of Ashe juniper to other woody species is an important feature of occupied golden cheeked- warbler habitat, particularly in the mid- to upper canopy at Fort Hood.

Monitoring Golden‐Cheeked Warblers on Private Lands in Texas

ABSTRACT A majority of North American breeding habitat for neotropical migrants exists on private lands, requiring monitoring strategies focused on habitat in these private holdings. We outline study designs and protocols using repeated Presence‐Absence surveys across a gradient of patch sizes to develop a range‐wide monitoring program for the endangered golden‐cheeked warbler (Dendroica chrysoparia) in Texas, USA. We surveyed 200–400 point‐count locations across approximately 30 private properties annually from 2005 to 2008. We used data from our surveyed patches (n = 147) and the Ψ (occupancy), p (detection), and γ = 1 ‐ ɛ parameterization to estimate patch dynamics and associated detection probabilities for golden‐cheeked warblers. Patch size had a strong association with patch occupancy, and all patches &gt;160 ha were predicted to be occupied. We found no evidence that large golden‐cheeked warbler populations located on public lands in the vicinity of our study area influenced occupancy dynamics. We conducted simulations across a range of detection probabilities to evaluate potential sample sizes for both standard‐ and removal‐based occupancy modeling. Simulations using parameter estimates from our analysis indicated that removal‐based sampling is superior to standard sampling. Based on our results, surveying golden‐cheeked warbler presence in oak‐juniper (Quercus‐Juniperus) patches under a removal modeling framework should be considered as one alternative for range‐wide monitoring programs because patch‐level monitoring would be necessary to estimate proportion of range occupied. Large contiguous patches are rare across the species’ range; hence, conservation and management of the mosaic of smaller patches within a landscape context would be required for maintaining species viability. Thus, we recommend the identification of areas where smaller, contiguous patches represent a significant portion of the available habitat within the local landscape and targeting these areas for habitat maintenance and improvement.

Evidence of a Minimum Patch Size Threshold of Reproductive Success in an Endangered Songbird

ABSTRACT That area‐sensitive songbirds breed only in relatively large patches suggests that there may be a minimum patch size threshold in which they will breed, even when controlling for the total amount of habitat in the landscape. We searched for minimum patch size thresholds of presence, territory establishment by males, pairing success, and reproductive success for 2 migratory songbirds that differed in sensitivity to patch size: golden‐cheeked warblers (Dendroica chrysoparia) and white‐eyed vireos (Vireo griseus). We assessed 2 potential limiting factors: brown‐headed cowbird (Molothrus ater) parasitism and arthropod biomass (food resource). We determined whether either factor was related to patch size and compared measurements of each above and below the observed thresholds. We monitored 24 golden‐cheeked warbler and 47 white‐eyed vireo territories in 12 patches. We found evidence of a minimum patch size threshold (between 15.0 ha and 20.1 ha) of reproductive success for golden‐cheeked warblers, but not for white‐eyed vireos. We found no minimum patch size thresholds for presence, territory establishment by males, or pair formation for either species. Conservation practices based on thresholds of presence, territory establishment, or pair formation might not address issues of reproduction for golden‐cheeked warblers. We failed to find evidence that cowbird parasitism or arthropod biomass were limiting factors. The ability to identify patch size thresholds of reproductive success for target species could be useful in conservation and management for setting goals for retention and restoration of target species’ habitat patch size.

Nocturnal Predation of Females on Nests: An Important Source of Mortality for Golden-Cheeked Warblers?

We monitored 124 female Golden-cheeked Warblers (Dendroica chrysoparia) at 133 nests with video cameras from 1997–2002 and 2005– 2006 at two study areas in central Texas, USA. Six adult females were depredated by snakes in 781 camera-monitored intervals when females were on the nest at night and exposed to possible nocturnal predation. Daily nest survival was 0.971 (95% CI: 0.959–0.980) and daily adult female predation while nesting was 0.008 (95% CI: 0.003–0.017). We estimated that 14.6% of breeding females were depredated on the nest during the breeding season based on the observed survival rates and assuming females whose first nest was unsuccessful and which survived attempted a second nesting attempt. Females were captured 75% of the times they were on the nest at the time of a nocturnal nest predation by a snake. Predation of nesting females is potentially an important source of mortality for Golden-cheeked Warblers, and warrants further investigation.