Sink or swim? Viability of a black-tailed godwit population in relation to flooding

1. Godwits of the Limosa l. limosa race have declined throughout northern Europe because of changing agricultural practices. The relict UK population is now mostly confined to two reserves within flood-defence structures, and numbers have declined at one of these. This study diagnosed the cause of this decline and evaluated options for remedial management. 2. Re-nesting models showed that productivity varied among sites and years in relation to flooding patterns. Floods caused breeding failure by forcing godwits to nest on nearby arable fields where nest and chick survival rates were low. 3. A population model showed that flood-dependent variations in productivity were sufficient to explain the contrasting population trends at the two sites. 4. The relative merits of various options for mitigating the effect of floods on godwits were investigated using a combination of hydrological, re-nesting and population models. 5. Models assuming a closed population resulted in numbers of godwit pairs at one site, the Ouse Washes in eastern England, declining and becoming extirpated within 30 years under current conditions. Some management options improved productivity, population growth and persistence likelihood, but the chances of extirpation were still high and conservation targets would not be met. 6. Models assuming an open population showed that target populations would only be achieved within 30 years if all of the available flood mitigation options were combined. However, habitat creation outside the Ouse Washes resulted in comparable productivity and population growth at a fraction of the cost. 7. Synthesis and applications. Provision of compensatory habitat is likely to be a more parsimonious means of conserving black-tailed godwits at the Ouse Washes than flood mitigation. However, reliance on the creation of new habitat is a more risky strategy as the godwits may continue to use traditional arable fields in favour of grassland alternatives, and because their productivity on created grassland is unknown.