Impacts of colonial waterbirds on vegetation and potential restoration of island habitats

Abstract

Colonial waterbirds have impacted forested island ecosystems throughout their breeding range, changing vegetation, and soil characteristics and bird communities. Our objectives were to (1) determine effects of three levels of colonial waterbird exclusion on overall vegetation diversity and growth, and survival of a candidate restoration species (black elderberry; Sambucus nigra canadensis); (2) investigate effects of different planting techniques on survival and growth of black elderberry; and (3) determine effects of waterbird colonization on soil chemistry. In 2012, we investigated effects of three levels of waterbird exclusion (none control plots [CON]; partial, which excluded waterbirds larger than gulls [PEX]; and full which excluded all waterbirds [FEX]) on bird use, existing vegetation growth and diversity, and survival of planted black elderberry on three islands in Door County, WI, Lake Michigan. In 2013, we evaluated survival of black elderberry established with four planting treatments within three waterbird exclusion treatments on two islands in 2013. We also compared soil chemistry characteristics between islands with and without nesting waterbirds for 2 years. Overall plant growth was greater in exclosures, but elderberry survival was similar among treatments. Soil replacement and weed suppression planting treatments did not affect survival, but generally increased overall elderberry biomass. Soil from nesting islands was more acidic and had greater nutrient concentrations than reference islands. Exclusion or removal of colonial nesting waterbirds from islands may improve overall vegetation growth, but successful restoration of woody vegetation may require significant soil manipulation and planting.

Long‐term impact of protected colonial birds on a jeopardized cork oak population: conservation bias leads to restoration failure

“…Detrimental effects exerted by the waterbird colony were not limited to large CO, but also markedly affected the health and survival of non-centenarian oaks (see Ayers et al 2015). The higher colony occupation of planted oaks as compared to naturally regenerated ones seems related to the clumped distribution and proximity to 1965 1970 1975 1980 1985 1990 1995 Ramo, unpublished data).…”

Double-crested cormorant colony effects on soil chemistry, vegetation structure and avian diversity

“…Double-crested Cormorants (Phalacrocorax auritus, cormorant) have the capacity to affect soil properties within their nesting colonies (Rush et al, 2011;Dorr et al, 2014;Lafferty et al, 2016). Changes in soil qualities such as nutrient concentrations and pH can disrupt plant germination and promote invasive vegetation (Cuthbert et al, 2002;Boutin et al, 2011;Ayers et al, 2015). Habitat changes borne through cormorant nesting activities includes simplification of habitat structure by suppressing the presence and growth of sensitive species and the homogenization of species composition, (Ishida, 1996;Hebert et al, 2005;Breuning-Madsen et al, 2010;Boutin et al, 2011).…”

Double‐Crested Cormorants: Too Much of a Good Thing?

“…These impacts can be relatively rapid (tree mortality in 3-10 years). Changes in soil have been shown to affect plant species composition, resulting in reduced number of species and opportunity for exotic, invasive plants (Ayers et al 2015), as well as impacts to arthropod communities (Craig et al 2012). Hebert et al (2014) documented significant damage to trees on forested islands associated with cormorant nesting and that vegetation damage can negatively impact co-nesting avian species that are obligate tree nesters.…”

“…Cormorants have caused extensive damage to vegetation where they nest due to excessive guano, associated soil chemistry changes, and physical destruction (Hebert et al 2014;Ayers et al 2015;Lafferty et al 2016; Figure 5). These impacts can be relatively rapid (tree mortality in 3-10 years).…”