Cumulative Human Impacts on biRd Populations (CHIRP): A multi-tiered approach to conserving the near-threatened Eurasian Oystercatcher

Abstract

The Eurasian Oystercatcher (Haematopus ostralegus) is a partially migratory meadow bird, and wading bird, that has declined substantially in recent decades. The cause of the decline may be due to several threats which vary in space and time. For example, some threats occur principally in winter like climate change, human disturbance or competition whilst others occur in summer, of which some only occur inland like agricultural intensification whilst shellfisheries or flooding are in coastal areas. Therefore, the relative impact of these threats, and how these impacts accumulate across the annual cycle will depend upon where an individual is in space and time, i.e. where it breeds and winters. The project CHIRP aims to quantify these cumulative human impacts through several sub-projects that focus on threats during the winter and summer period and combines these into a migratory network metapopulation model. The metapopulation model aims to identify the relative, and cumulative, impact of these multiple threats so that conservation actions can be prioritised. In this talk we first describe CHIRP and then focus on the first results that describe seasonal survival and migratory connectivity of the oystercatcher. Collaborative colour-ringing projects between researchers and citizen scientists allowed us to track annual movements across large geographical areas. We have collected data from more than 4,600 oystercatchers with over 51,000 observations, predominantly by citizen scientists. We performed a seasonal multi-state (5 geographical areas within the Netherlands) live- and dead-recoveries analysis under varying model structures to account for biological and data complexity. Coastal breeding populations were largely sedentary but inland breeding populations were migratory. The direction of migration varied among areas, which has not been described previously. Our results indicated that survival was lower during spring than autumn and that survival was lower in inland areas compared with coastal areas. A concerning result was that survival of individuals over-wintering in the Wadden Sea, an internationally important site for over-wintering shorebirds, appeared to decline during the study period. We discuss the outcomes of our study, and how citizen science was integral for conducting this study. Our findings identify how the demographic rates of the oystercatcher vary in space and time, knowledge vital for generating hypotheses and prioritising future research into the causes of decline.