Vegetation growth spurt on Bird Island, Addo MPA, seems good for African penguin conservation
AFRICAN PENGUINS ON BIRD ISLAND, ADDO MPA ARE BENEFITING FROM INCREASED VEGETATION AFTER RECENT GOOD RAINS, WHICH IS ADVANTAGEOUS FOR THEIR BREEDING SUCCESS
African penguin nesting within lush growth (top) and using roots and stems of Mesembryanthemum aitonis (sea spinach) (bottom) on Bird Island, Algoa Bay. Lush vegetation after recent good rains is facilitating nest building by this endangered species (Photos: Cloverley Lawrence).
The breeding success of penguins is closely linked to the availability of suitable nesting habitats, which play a vital role in providing protection and regulating temperature. Unfortunately, the historical, widespread and excessive harvesting of guano, a crucial nesting material, resulted in a decrease in penguins digging burrows. Consequently, more penguins have resorted to nesting in the open or seeking refuge under vegetation cover. Surface nests expose penguins to disturbances, heat, and predators, while vegetation cover offers a measure of protection by providing shade during the hot summer months. This vegetation cover has positive effects on incubation, chick survival, and the long-term reproductive success of penguins.
Recently, the Eastern Cape has experienced an increase in rainfall due to the La Niña weather phenomenon. As a result, Bird Island, located in the Addo Elephant National Park Marine Protected Area (MPA), experienced flourishing vegetation, creating favourable conditions for the resident African penguin (Spheniscus demersus) colony, by providing cover for their nests. However, there were concerns about the potential proliferation of non-native plant species and the consequences for the penguins. To address these concerns, a survey was conducted during the peak summer season when vegetation cover was at its highest. Seventy four (2 m x 2 m; 296 m²) quadrats were sampled across six transect lines following a stratified random sampling approach.
The survey assessed the percentage cover of the substrate in each quadrant; vegetation, bare ground, sand, rocks, and dead roots. Additionally, all plants were counted, and their average and maximum heights measured.
Preliminary classifications using iNaturalist identified a total of 13 plant taxa contributing 86% of low (<1m) vegetation cover. This was dominated by two indigenous species, Mesembryanthemum aitonis (sea spinach) and Tetragonia sp. (sea corals), which collectively provided 80% cover through their densely interconnected root system. The maximum height of the vegetation recorded was 43.5 cm, with an average height of 20.2 cm. Six taxa identified as non-native were likely transported by wind or inadvertently brought to the island on shoes.
On average, five non-native plants/m² account for approximately 4% of overall vegetation cover, suggesting that they are not (yet) invasive. Chenopodiastrum murale (nettle-leaved goosefoot), belonging to the Amaranthaceae family, was the most abundant non-native species (342 plants). Originating from Europe, parts of Asia, and northern Africa, it contains diverse chemical constituents that have phytotoxic and insecticidal properties which deter the growth of other plants around or beneath its canopy. At the end of the growing season, the ground below these plants becomes exposed and vulnerable to flooding, which will require management intervention.
Penguins use the lush vegetation to make their nests in the undergrowth and/or use dried roots and stems of the two dominant plant species to line their nests. Magellanic Penguins (Spheniscus magellanicus) in Argentina, and Little Penguins (Eudyptula minor) in Western Australia have similarly benefited from higher vegetation nest cover, resulting in greater reproductive success. The presence of vegetation is thus crucial for improving penguin breeding by providing protection against predators and heat stress.
Recognizing the significance of vegetation cover for African penguins, and implementing long-term monitoring coupled with experimental approaches, including assessing the effects of alien species, can help gain deeper insights into the intricate factors influencing penguin nest selection.
This article was originally published in the 2022/2023 Research Report.
