The beginning of time? Evidence for catastrophic drought in Baringo in the early nineteenth century

New developments in the collection of palaeo-data over the past two decades have transformed our understanding of climate and environmental history in eastern Africa. This article utilises instrumental and proxy evidence of historical lake-level fluctuations from Baringo and Bogoria, along with other Rift Valley lakes, to document the timing and magnitude of hydroclimate variability at decadal to century time scales since 1750. These data allow us to construct a record of past climate variation not only for the Baringo basin proper, but also across a sizable portion of central and northern Kenya. This record is then set alongside historical evidence, from oral histories gathered amongst the peoples of northern Kenya and the Rift Valley and from contemporary observations recorded by travellers through the region, to offer a reinterpretation of human activity and its relationship to environmental history in the nineteenth century. The results reveal strong evidence of a catastrophic drought in the early nineteenth century, the effects of which radically alters our historical understanding of the character of settlement, mobility and identity within the Baringo–Bogoria basin

Invader removal triggers competitive release in a threatened avian predator

Changes in the distribution and abundance of invasive species can have far-reaching ecological consequences. Programs to control invaders are common but gauging the effectiveness of such programs using carefully controlled, large-scale field experiments is rare, especially at higher trophic levels. Experimental manipulations coupled with long-term demographic monitoring can reveal the mechanistic underpinnings of interspecific competition among apex predators and suggest mitigation options for invasive species. We used a large-scale before-after control-impact removal experiment to investigate the effects of an invasive competitor, the barred owl (Strix varia), on the population dynamics of an iconic old-forest native species, the northern spotted owl (Strix occidentalis caurina). Removal of barred owls had a strong, positive effect on survival of sympatric spotted owls and a weaker but positive effect on spotted owl dispersal and recruitment. After removals, the estimated mean annual rate of population change for spotted owls stabilized in areas with removals (0.2% decline per year), but continued to decline sharply in areas without removals (12.1% decline per year). The results demonstrated that the most substantial changes in population dynamics of northern spotted owls over the past two decades were associated with the invasion, population expansion, and subsequent removal of barred owls. Our study provides experimental evidence of the demographic consequences of competitive release, where a threatened avian predator was freed from restrictions imposed on its population dynamics with the removal of a competitively dominant invasive species

Demographic response of northern spotted owls to barred owl removal

Federally listed as threatened in 1990 primarily because of habitat loss, the northern spotted owl (Strix occidentalis caurina) has continued to decline despite conservation efforts resulting in forested habitat being reserved throughout its range. Recently, there is growing evidence the congeneric invasive barred owl (Strix varia) may be responsible for the continued decline primarily by excluding spotted owls from their preferred habitat. We used a long-term demographic study for spotted owls in coastal northern California as the basis for a pilot barred owl removal experiment. Our demography study used capture–recapture, reproductive output, and territory occupancy data collected from 1990 to 2013 to evaluate trends in vital rates and populations. We used a classic before-after-control-impact (BACI) experimental design to investigate the demographic response of northern spotted owls to the lethal removal of barred owls. According to the best 2-species dynamic occupancy model, there was no evidence of differences in barred or northern spotted owl occupancy prior to the initiation of the treatment (barred owl removal). After treatment, barred owl occupancy was lower in the treated relative to the untreated areas and spotted owl occupancy was higher relative to the untreated areas. Barred owl removal decreased spotted owl territory extinction rates but did not affect territory colonization rates. As a result, spotted owl occupancy increased in the treated area and continued to decline in the untreated areas. Prior to and after barred owl removal, there was no evidence that average fecundity differed on the 2 study areas. However, the greater number of occupied spotted owl sites on the treated areas resulted in greater productivity in the treated areas based on empirical counts of fledged young. Prior to removal, survival was declining at a rate of approximately 0.2% per year for treated and untreated areas. Following treatment, estimated survival was 0.859 for the treated areas and 0.822 for the untreated areas. Derived estimates of population change on both study areas showed the same general decline before removal with an estimated slope of –0.0036 per year. Following removal, the rate of population change on the treated areas increased to an average of 1.029 but decreased to an average of 0.870 on the untreated areas. The results from this first experiment demonstrated that lethal removal of barred owls allowed the recovery of northern spotted owl populations in the treated portions of our study area. If additional federally funded barred owl removal experiments provide similar results, this could be the foundation for development of a long-term conservation strategy for northern spotted owls.This is the publisher’s final pdf. The article is copyrighted by the Wildlife Society and published by John Wiley & Sons, Inc. It can be found at: http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291937-2817Keywords: barred owl, removal experiment, northern spotted owl, demography, competitio

Range-wide sources of variation in reproductive rates of northern spotted owls

We conducted a range-wide investigation of the dynamics of site-level reproductive rate of northern spotted owls using survey data from 11 study areas across the subspecies geographic range collected during 1993–2018. Our analytical approach accounted for imperfect detection of owl pairs and misclassification of successful reproduction (i.e., at least one young fledged) and contributed further insights into northern spotted owl population ecology and dynamics. Both nondetection and state misclassification were important, especially because factors affecting these sources of error also affected focal ecological parameters. Annual probabilities of site occupancy were greatest at sites with successful reproduction in the previous year and lowest for sites not occupied by a pair in the previous year. Site-specific occupancy transition probabilities declined over time and were negatively affected by barred owl presence. Overall, the site-specific probability of successful reproduction showed substantial year-to-year fluctuations and was similar for occupied sites that did or did not experience successful reproduction the previous year. Site-specific probabilities for successful reproduction were very small for sites that were unoccupied the previous year. Barred owl presence negatively affected the probability of successful reproduction by northern spotted owls in Washington and California, as predicted, but the effect in Oregon was mixed. The proportions of sites occupied by northern spotted owl pairs showed steep, near-monotonic declines over the study period, with all study areas showing the lowest observed levels of occupancy to date. If trends continue it is likely that northern spotted owls will become extirpated throughout large portions of their range in the coming decades

Range-wide declines of northern spotted owl populations in the Pacific Northwest: A meta-analysis

The northern spotted owl (Strix occidentalis caurina) inhabits older coniferous forests in the Pacific Northwest and has been at the center of forest management issues in this region. The immediate threats to this federally listed species include habitat loss and competition with barred owls (Strix varia), which invaded from eastern North America. We conducted a prospective meta-analysis to assess population trends and factors affecting those trends in northern spotted owls using 26 years of survey and capture-recapture data from 11 study areas across the owls\u27 geographic range to analyze demographic traits, rates of population change, and occupancy parameters for spotted owl territories. We found that northern spotted owl populations experienced significant declines of 6–9% annually on 6 study areas and 2–5% annually on 5 other study areas. Annual declines translated to ≤35% of the populations remaining on 7 study areas since 1995. Barred owl presence on spotted owl territories was the primary factor negatively affecting apparent survival, recruitment, and ultimately, rates of population change. Analysis of spotted and barred owl detections in an occupancy framework corroborated the capture-recapture analyses with barred owl presence increasing territorial extinction and decreasing territorial colonization of spotted owls. While landscape habitat components reduced the effect of barred owls on these rates of decline, they did not reverse the negative trend. Our analyses indicated that northern spotted owl populations potentially face extirpation if the negative effects of barred owls are not ameliorated while maintaining northern spotted owl habitat across their range

Northern spotted owl reproductive rates

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis.The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan

Northern spotted owl reproductive rates (version 2)

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis. The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates

Northern spotted owl reproductive rates (version 3)

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis. The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates.Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates.Version 3 has the same information as version 3, with the following changes: (1) Updated full list of models .csv to reflect updated analysis. (2) Updated the data files (.pao and seascov.csv) for the COA study area – all other study areas have not changed