Data from: Northern flickers only work when they have to: how individual traits, population size and landscape disturbances affect excavation rates of an ecosystem engineer

Woodpeckers are considered ecosystem engineers because they excavate tree cavities which are used subsequently by many species of secondary cavity nesters for breeding. Woodpeckers have the choice of excavating a new hole or reusing an existing one, and this propensity to excavate (e) may affect community dynamics but has rarely been investigated. Using 18 years of data on a population of northern flickers Colaptes auratus, I tested six hypotheses to explain the propensity to excavate (e) in a landscape which experienced two types of disturbance: pine beetles and wildfires. Woodpecker age, breeding experience and mate retention had little influence on e which varied between 13-39% annually and averaged 23% for 1843 first nests over the 18 years. Body size and body condition of males and females were not associated with e but rates of excavation declined seasonally, suggesting time rather than energy costs limited excavation effort. Reduced cavity availability mediated through high conspecific density coupled with wildfires triggered relatively high excavation rates, up to 39% but e decreased to baseline levels three years after the landscape disturbances. Nearly 2/3 of males did not excavate in their lifetime but apparently, e is great enough to balance the average rate of cavity tree loss in this forest which is 11% annually. Excavation propensity in flickers is flexible, but the birds reduce their work levels if there is a surplus of holes available.

啄木鸟被视为生态系统工程师（ecosystem engineers），它们开凿的树洞会被众多次级洞巢鸟类（secondary cavity nesters）后续用于繁殖。啄木鸟可选择开凿新树洞或复用已有树洞，而这种开挖倾向（e）可能会影响群落动态，但相关研究却极少开展。本研究基于18年的北扑翅鴷（Colaptes auratus）种群数据，针对经历了松甲虫（pine beetles）与野火两种干扰的景观，检验了6个用以解释开挖倾向（e）的假说。

啄木鸟的年龄、繁殖经验以及配偶留存情况对e几乎无影响；e的年度占比在13%至39%之间波动，在18年间的1843个首巢中平均占比为23%。雌雄个体的体型与身体状况均与e无显著关联，但开挖率随季节逐渐下降，这表明限制开挖行为的因素是时间而非能量成本。

由较高的同种个体密度介导的树洞可获得性下降，叠加野火事件，触发了相对较高的开挖率，最高可达39%；但在景观干扰发生三年后，e回落至基线水平。近2/3的雄性个体终身未进行树洞开挖，但显然整体的e水平足以抵消该森林每年11%的树洞枯损率。

北扑翅鴷的开挖倾向具有可塑性，但当树洞供给过剩时，它们会降低开挖强度。