Title: Group size mediates effects of intraspecific competition and forest structure on productivity in a recovering social woodpecker population

Abstract

Conservation of endangered social wildlife in disturbance-prone forests is challenging because direct and indirect effects of management strategies developed at the time of species’ listing when population density is low may change under high-density conditions in locally recovered populations. Here, we used piecewise structural equation modeling to evaluate direct and indirect drivers of productivity in the federally endangered cooperatively breeding red-cockaded woodpecker Dryobates borealis (RCW) on Savannah River Site, South Carolina, USA. We estimated direct and indirect relationships among group size, neighboring group sizes, fledgling production, density of cavity tree clusters occupied by RCWs, area satisfying threshold criteria of ≥22 stems ha^–1 of pines ≥35.6 cm diameter at breast height (dbh), <1.4 m² ha^–1 basal area (BA) of hardwoods 7.6–22.9 cm dbh, and <6% hardwood canopy cover, and area treated with prescribed fire, and tested whether group size mediated indirect effects of area satisfying threshold criteria on fledgling production. Increases in area with ≥22 stems ha^–1 of pines ≥35.6 cm dbh and <1.4 m² ha^–1 BA of hardwoods 7.6–22.9 cm dbh, and area treated with prescribed fire, but not area with <6% hardwood canopy cover, had direct positive effects on group size. Group size and area treated with prescribed fire,more » but not area satisfying threshold criteria, had direct positive effects on fledgling production. The direct effect of neighboring group sizes on fledgling production was negative and smaller relative to the direct positive effect of group size on fledgling production. Overall, our results indicate positive direct effects of group size on fledgling production outweighed negative direct effects of neighboring group sizes, and that group size mediated positive indirect effects of area satisfying structural threshold criteria on fledgling production. These findings indicate that ongoing forest management aimed to increase area with ≥22 pines ha^–1 ≥35.6 cm dbh and <1.4 m² ha^–1 BA of hardwoods 7.6–22.9 cm dbh will promote large group sizes, which in turn improve fledgling production and offset costs of heightened competition with neighboring groups under high-density conditions. Additionally, positive effects of area treated with prescribed fire on RCW group size and fledgling production indicate prescribed fire has unique contributions to woodpecker productivity, likely via direct effects on forest structure and potentially indirect effects on arthropod prey available to foraging RCWs. Furthermore, by simultaneously accounting for multiple drivers of productivity in social wildlife, our study contributes to the understanding of how increases in social wildlife population sizes can alter previously documented habitat-fitness relationships.« less

Authors:

Garabedian, James E.  ^[1];

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Moorman, C. E. ^[2]; Peterson, M. N. ^[2]; Kilgo, J. C. ^[1]

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+ Show Author Affiliations

1. USDA Forest Service Southern Research Station, New Ellenton, SC (United States)
2. North Carolina State Univ., Raleigh, NC (United States)

Publication Date:

Sat Nov 20 00:00:00 EST 2021

Research Org.:

USDA Forest Service Southern Research Station, New Ellenton, SC (United States)

Sponsoring Org.:

USDOE Office of Environment, Health, Safety and Security (AU)

OSTI Identifier:

1846588

Report Number(s):

22-01-P
Journal ID: ISSN 1367-9430; SRS 15‐CS‐11083601‐001; TRN: US2302553

Grant/Contract Number:  

EM0003622

Resource Type:

Accepted Manuscript

Journal Name:

Animal Conservation

Additional Journal Information:

Journal Volume: 25; Journal Issue: 3; Journal ID: ISSN 1367-9430

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES; cooperative breeder; endangered species; indirect effects; population density; prescribed fire; structural equation model; woodpecker