Eiders, nutrients and eagles: Bottom‐up and top‐down population dynamics in a marine bird

Abstract

The main objective of this long‐term study (1978–2016) was to find the underlying factors behind the declining trends of eider Somateria mollissima in the Baltic/Wadden Sea. Specifically, we aimed at quantifying the bottom‐up effect of nutrients, through mussel stocks, on reproduction and abundance of eider, and the top‐down effects caused by white‐tailed eagle Haliaeetus albicilla predation. Bottom‐up effects increase marine primary productivity with subsequent effects on food availability for a major mussel predator. Top‐down effects may also regulate eider populations because during incubation female eiders are vulnerable to predation by eagles. Our structural equation modelling explained a large percentage of the variance in eider abundance. We conclude that the Baltic/Wadden Sea eider population was regulated directly by white‐tailed sea eagle predation on incubating females and indirectly by the amount of nutrients in seawater affecting both mussel stocks and the breeding success of eiders, reflecting density dependence. These findings may explain the decreasing trend in the Baltic/Wadden Sea eider population during the last decades as an additive effect of top‐down and bottom‐up factors, and likely as an interaction between them.

Large-scale changes in marine and terrestrial environments drive the population dynamics of long-tailed ducks breeding in Siberia

“…A relation found between fertilizers and mussels on the Wadden Sea would indicate that the availability of dissolved nutrients (DIN and DIP as linked to fertilizer use 58 ) can be used as a proxy for mussel abundance and quality in the southern Baltic Sea. The results shown for other seabird populations in that region 70 , 71 support this reasoning.…”

“…5 ). The processes influencing long-tailed duck populations in these two habitats hypothetically are driven by different ecological interactions, for example predator-driven on the breeding grounds 12 , 14 , 80 and resource-driven on the wintering grounds 45 , 58 , 70 , 71 . For example, precipitation evidently influences lemming dynamics on the breeding grounds while temperature and nutrient runoff from the land are thought to affect mussel reproduction, growth and survival on the wintering grounds.…”

Annual variation in breeding success in boreal forest grouse: Four decades of monitoring reveals bottom‐up drivers to be more important than predation

“…Some long‐term studies have examined aspects of breeding in birds (e.g., song sparrows (Arcese et al, 1992); Seychelle warblers (Brouwer et al, 2012); acorn woodpeckers (Koenig et al, 2011); white‐throated dippers (Nilsson et al, 2011); eiders (Coulson, 2010; Morelli et al, 2021)), but causes of variation in avian breeding success have largely been inferred from short‐term, single‐factor correlations. In Eurasian boreal forest grouse, no previous study has looked at several potential factors operating simultaneously on the same population over a long period.…”

“…Aiming to identify the main drivers of annual variation in reproduction, we examine how breeding success varied with a range of bottom-up and top-down factors in two species of Eurasian boreal forest grouse, the capercaillie (Tetrao urogallus) and the black grouse (T. tetrix). Some long-term studies have examined aspects of breeding in birds (e.g., song sparrows (Arcese et al, 1992); Seychelle warblers (Brouwer et al, 2012); acorn woodpeckers (Koenig et al, 2011); white-throated dippers (Nilsson et al, 2011); eiders (Coulson, 2010;Morelli et al, 2021)), but causes of variation in avian breeding success have largely been inferred from short-term, single-factor correlations. In Eurasian boreal forest grouse, no previous study has looked at several potential factors operating simultaneously on the same population over a long period.…”

Health Status of Bycaught Common Eiders (Somateria mollissima) from the Western Baltic Sea

“…Due to these ongoing declines, the European population is now listed as endangered [ 1 ]. Many factors may be contributing to the observed decline, including increased predation pressure [ 12 , 13 , 14 ], inappropriate hunting management [ 11 ], reduction in food availability linked to natural yearly fluctuations in mussel stocks, and intensification of commercial mussel exploitation [ 15 , 16 , 17 ], as well as Pasteurella (P.) multocida epidemics [ 18 , 19 ].…”