Fall 2007: Volume 28, Number 4 - Missouri Prairie Foundation

Cone-of-VulnerabilityRobert N. Chapmannerability. Cone-of-vulnerability describes anindividual’s vulnerability to avian predators.Imagine a cone-shaped volume of space above aquail head. As altitude increases, the volume ofthe cone increases. Therefore the wider the cone,the more vulnerable the quail will be to detectionby an avian predator. The cone-of-vulnerabilitycan be reduced by providing maximum usablespace through habitat management. Many speciesof native grass have an umbrella-like growthstructure, especially the bunch-type grasses likelittle bluestem, broomsedge and dropseeds. Notonly do these grasses provide excellent nestingstructure, they also serve to reduce the exposureof quail and their young to avian predators. Thelong leaves of bunch grasses grow up and out,resulting in a canopy over the space betweenthe clumps. The space between the grass clumpscontains ample bare ground for increased mobilityand is where many plant species that providefood grow. The plants that grow in these spacescontribute to a field’s vegetation diversity, whichin return increases insect biomass, the criticalfood item for growing quail chicks. Low-growingshrubs such as sumacs, American plum, gray andRobert N. Chapman Robert N. ChapmanThe above left photoof a prescribed prairiefire reveals burnedclumps of little bluestemgrass, in or againstwhich quail and otherground-nesting birds willnest. The photo at leftillustrates the umbrellalikegrowth structureof little bluestem; bygrowing up and out,the leaves of this andother native bunchtypegrasses create acanopy under whichquail can travel “undercover,” reducing a quail’scone-of-vulnerability,as illustrated above. Inbetween grass clumps,bare ground providesquail chicks with travellanes, and other plantspecies, such as thelegumes shown in thelower left photo, growand attract insects andprovide seeds, both ofwhich are eaten by quail.17