Complexity of factors affecting bobolink population dynamics communicated with directed acyclic graphs

Abstract

North American grassland birds experienced steeper, more consistent, and widespread declines than other avian guilds in the past quarter century. Despite the surge of research into their ecology and conservation, there remains considerable uncertainty about the proximate and ultimate causes of declines and a need to clearly communicate its structural complexity among policy makers, resources managers, and stakeholders. We organized evidence from published literature about factors affecting population dynamics of bobolink (Dolichonyx oryzivorus), augmented by local stakeholder knowledge, in directed acyclic graphs (DAGs) depicting hypothesized cause-effect relationships. Our contrast between states of knowledge as depicted in the literature and among stakeholders revealed several factors and relationships not in evidence in the other. For example, stakeholders identified 3 secondary factors alleged to affect bobolink habitat quantity on breeding grounds not identified in the literature: tree planting incentives, green energy incentives, and crop values. These and other structural uncertainties in the management systems are made transparent using DAGs, facilitating communication and co-learning among knowledge holders. Accounting for structural complexity and making it transparent at the outset of the planning and decision-making process may reduce the probability of unanticipated outcomes as a result of poor management choices. Ó 2017 The Wildlife Society.

Bobolink (Dolichonyx oryzivorus) Declines Follow Bison (Bison bison) Reintroduction on Private Conservation Grasslands

“…The presence of active grazing in grasslands may decrease birds’ nest success, in part because unlike adult birds, nests and chicks cannot move to avoid being trampled or depredated, and many grassland bird species appear to avoid nesting in grasslands with active grazing [ 97 ]. Because Bobolinks nest on the ground, the presence of active grazing and its impacts directly affect Bobolinks’ potential for successfully nesting and raising juvenile birds until they develop flight skills and independence [ 27 , 42 ]. In rotational grazing systems in Vermont, for example, predation and trampling by cattle accounted for a significant proportion (32%) of nest failures, significantly lowering Bobolink productivity [ 99 ].…”

“…Colder Januarys may indirectly affect vegetation production via soil moisture, if temperatures are sufficiently low that the soil remains frozen for most of the winter, and soil water levels do not recharge until spring. Conversely, warmer temperatures and increased precipitation directly contribute to increases in arthropods [ 42 , 89 ], plants, and seeds [ 101 , 102 , 110 ] that provide a large proportion of Bobolinks’ food. Vegetation type, height, heterogeneity and density all play direct roles in availability of nest locations for birds [ 89 ], level of nest cover [ 44 ], concealment from predators ([ 110 ]; but see [ 111 ]), availability of singing perches for males [ 110 ], and in mitigating the impacts of extreme weather events or periods of resource scarcity [ 112 , 113 ].…”

“…Bobolink conservation priorities include identifying and fostering conditions on the breeding grounds that improve their productivity [ 37 ]. Primary factors driving Bobolink declines include the conversion of grasslands to row agriculture and associated habitat loss and degradation on their breeding grounds, where they often build nests at the base of large flowering plants [ 38 , 41 , 42 ]. Although Bobolinks disperse from heavily grazed grasslands [ 43 , 44 ], past research has suggested that light grazing by bison may be compatible with Bobolink conservation [ 45 ].…”

Rotational grazing of beef cattle to support Bobolink breeding success

“…The provincial government plan states that the current population cannot be maintained because of habitat loss on agricultural land and instead aims to maintain the population at 65% of its estimated size in 2015 (OMNRF 2015), which may be larger than the population prior to European settlement (COSEWIC 2010). Probable causes of the Bobolink population decline include habitat loss and a decrease in habitat quality on breeding grounds (COSEWIC 2010, McCracken et al 2013, OMNRF 2015, Ethier and Nudds 2017. Habitat quality on breeding grounds can be poor because of agricultural practices (e.g., hay harvest and livestock grazing) that result in direct and indirect destruction of nests (Bollinger et al 1990, Perlut et al 2006, MacDonald and Nol 2017.…”

Finding clarity in ecological outcomes using empirical integrated social–ecological systems: A case study of agriculture‐dependent grassland birds

“…For example, integrated conceptual approaches can generate novel hypotheses regarding distal anthropogenic causes of ecological phenomena simply by following the chain of causality backwards (e.g. Ethier & Nudds, 2017; Hughes et al., 2017). In our case study, climate was identified as a previously unsuspected upstream (exogenous) moderator of annual variation in farm management and Grasshopper Sparrow population growth rate fluctuations.…”