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Reproductive success of the threatened San Clemente Bell's Sparrow in recovering habitats is similar to success in historical habitat

Citation

Meiman, Susan; DeLeon, Emma; Bridges, Andrew (2021), Reproductive success of the threatened San Clemente Bell's Sparrow in recovering habitats is similar to success in historical habitat, Dryad, Dataset, https://doi.org/10.5061/dryad.931zcrjg5

Abstract

The San Clemente Bell’s Sparrow Artemisiospiza belli clementeae is a federally threatened subspecies endemic to San Clemente Island, California. Previous research suggested dependence on boxthorn (Lycium californicum) as breeding habitat and nesting substrate; however, this conclusion was based on data collected when introduced feral ungulates had severely degraded the soil and vegetation cover. Since removal of the ungulates, native vegetation has gradually increased and the San Clemente Bell’s Sparrows have expanded into areas where habitat had been unsuitable. To explore how Bell’s Sparrows use these areas, we examined reproductive metrics associated with habitat covariates gathered at 214 nest sites used by Bell’s Sparrows from 2014 ̶ 2016. We found that nest success in boxthorn habitat, previously considered an essential habitat for Bell’s Sparrow nesting, was similar to success in alternative habitat types. Our findings contradict previous conclusions that Bell’s Sparrows were boxthorn-dependent. We believe this previously documented relationship was likely due to the lack of available alternative nesting habitat following years of feral ungulate degradation, and Bell’s Sparrows now reproduce in multiple habitat types and throughout most of San Clemente Island. Furthermore, our findings illustrate the importance of long-term monitoring and corresponding adaptive management when monitoring species in changing and recovering landscapes.The San Clemente Bell’s Sparrow Artemisiospiza belli clementeae is a federally threatened subspecies endemic to San Clemente Island, California. Previous research suggested dependence on boxthorn (Lycium californicum) as breeding habitat and nesting substrate; however, this conclusion was based on data collected when introduced feral ungulates had severely degraded the soil and vegetation cover. Since removal of the ungulates, native vegetation has gradually increased and the San Clemente Bell’s Sparrows have expanded into areas where habitat had been unsuitable. To explore how Bell’s Sparrows use these areas, we examined reproductive metrics associated with habitat covariates gathered at 214 nest sites used by Bell’s Sparrows from 2014 ̶ 2016. We found that nest success in boxthorn habitat, previously considered an essential habitat for Bell’s Sparrow nesting, was similar to success in alternative habitat types. Our findings contradict previous conclusions that Bell’s Sparrows were boxthorn-dependent. We believe this previously documented relationship was likely due to the lack of available alternative nesting habitat following years of feral ungulate degradation, and Bell’s Sparrows now reproduce in multiple habitat types and throughout most of San Clemente Island. Furthermore, our findings illustrate the importance of long-term monitoring and corresponding adaptive management when monitoring species in changing and recovering landscapes.

Usage Notes

Dataset: BESP_Nest_Fate-MARK.csv
This file contains data collected at each nest site for input into MARK program. Individual covariates: Year of nest and habitat characteristics of each nest at 4 scales.
NestID = Unique ID for each nest in the sample
Day_of_Season_Start= Day of breeding season nest was first monitored
Day-of_Season_Last_Active= Day of breeding season when nest was still active
Day_of_Season_Nest_End_Monitoring= Day of breeding season nest successfully fledged OR day failure was documented
Nest Fate: 1=Failed, 0=Successfully fledged at least 1 chick
Encounters = 1
Historic_Habitat= Covariate for historic habitat (1=historically delineated Bell's sparrow habitat, 0=outside historic habitat)
Year_2014: 1=nest during year 2014
Year_2015: 1=nest during year 2015
Plot_Category_Boxthorn: 1=Boxthorn plot-scale habitat category.
Plot_Category_Mixed Shrub: 1=Mixed-Shrub plot-scale habitat category.
Substrate_Boxthorn: 1=Boxthorn Substrate-scale habitat category.
Substrate_Non-boxthorn Shrub: 1=Non-boxthorn substrate-scale habitat category.
MeanVegHt-15mRadius: Mean of vegetation height measured in 15m radius around nest at 1m intervals in 4 cardinal directions.
MeanShrubHt-15mRadius: Mean of shrub height measured in 15m radius around nest at 1m intervals in 4 cardinal direction.
ProportionBoxthorn-15m: Proportion of measurements around nest in 15m radius that are boxthorn.
ProportionShrub-15m: Proportion of measurements around nest in 15m radius that are shrub.    
ProportionNonboxthornShrub-15m: Proportion of measurements around nest in 15m radius that are shrub but not boxthorn.
Proportion Bare-15m: Proportion of measurements around nest in 15m radius that are bare ground.
Ratio_Bare_Ground_to_Shrub-15m: Ratio of proportions of bare ground/shrub cover.
15m-Category_Boxthorn: 1=Boxthorn habitat category at 15m.
15m_Category_Nonboxthorn_Shrub: 1=Non-boxthorn shrub category.

Dataset: BESP_Nests_Clutches.csv
This file contains data for clutch sizes of nests with eggs.
NestID = Unique ID for each nest in the sample
Historic_Habitat= Covariate for historic habitat (1=historically delineated Bell's sparrow habitat, 0=outside historic habitat)
Plot_Category: Habitat category assigned to plot in which nest was located (Boxthorn, Mixed Shrub, or Other).
Substrate_Category: Habitat category of nest substrate vegetation (Boxthorn, Non-boxthorn shrub, or Other).
15m_Category: Habitat category of 15m radius around the nest (Boxthorn, Non-boxthorn Shrub, or Nonshrub)
Clutch_Size: Size of clutch.

Dataset: BESP_Nests_Fledglings.csv
This file contains data for number of fledglings per successful nest.
NestID = Unique ID for each nest in the sample
Historic_Habitat= Covariate for historic habitat (1=historically delineated Bell's sparrow habitat, 0=outside historic habitat)
Plot_Category: Habitat category assigned to plot in which nest was located (Boxthorn, Mixed Shrub, or Other).
Substrate_Category: Habitat category of nest substrate vegetation (Boxthorn, Non-boxthorn shrub, or Other).
15m_Category: Habitat category of 15m radius around the nest (Boxthorn, Non-boxthorn Shrub, or Nonshrub)
Fledglings: Number of fledglings.