9th August 2019

Flying-foxes might want their cake but should they eat it too?

The Kate Barlow Award was set up in 2015 and aims to encourage postgraduate students to conduct a substantive bat research project and to honour the late Dr Kate Barlow's contribution to bat conservation. Laura Ann Pulscher (University of Sydney) was the 2018 winner and has just sent us this update:

The Christmas Island Flying-fox (Pteropus melanotus natalis; CIFF) is the last endemic mammal on Christmas Island (CI) and is critically endangered. While factors leading to its decline are not well understood, nutritional imbalances stemming from preferential consumption of introduced plants have been theorized as a contributing factor leading to its decline. Nearly 30% of CI has been cleared for phosphate mining and human settlement and much of this area has been re-vegetated with non-native plants many of which the CIFF forages on. Limited studies suggest that non-native food sources contain less energy, protein, and essential minerals such as calcium, iron and sodium in comparison to native food sources,1 thus reliance on non-native food plants could ultimately contribute to nutritional imbalances and reduced fitness in flying-foxes. With help from the Kate Barlow Award provided by Bat Conservation Trust, this study aimed to determine how CIFFs historically utilized native plants to meet their nutritional requirements and if nutritional content of non-native food plants differ from native food plants.

Common food plants (nectar, fruit, leaves, stems, and petioles) consumed by the CIFF were collected from May 2018 – February 2019 on CI. Nectar and fruit juice was assessed for sugar content and remaining fruit, leaves, stems, and petioles were submitted to a commercial laboratory for nutritional analysis. Results showed that non-native fruit on average had lower percentages/concentrations of crude protein, calcium, magnesium, sodium, copper, iron and manganese but higher carbohydrates, moisture, and zinc. In comparison to fruit, native leaves had higher percentages/concentrations of crude protein, calcium, magnesium, sodium, copper, and manganese but lower carbohydrates, iron, and zinc. Sugar content did not vary between native and non-native flowers or fruit.

This data provides evidence of what CIFF historically consumed to meet their nutritional demands and how the introduction of non-native food sources could impact nutritional imbalances in the population. Nutritional analysis of native food sources indicated that CIFFs historically obtained the bulk of their energy from fruit and nectar, however these food sources have minimal protein and calcium required for energy, growth, and reproduction.2 Therefore, CIFFs likely supplemented their diets with leaves, petioles, stems, and pollen which are rich sources of essential minerals and protein. In comparison to native fruits, non-native fruit, on average, contained less protein and essential minerals but higher carbohydrates. Thus, if the CIFF is preferentially consuming non-native food plants they may not meet nutritional requirements or they may overconsume carbohydrates in order to meet protein demands resulting in obesity in the population. A few non-native fruit species had nutritional content similar to native fruit and therefore may be an important non-native food source in the CIFF diet. When choosing plants to re-vegetate mined areas we recommend choosing native food plants or non-native food plants with similar nutritional profiles to maximize nutrition in the population.

The introduction of non-native vegetation is not a unique problem to Christmas Island and is seen all over the world. This study supports the theory that many non-native plants are nutritionally deficient which could lead to decreased fecundity and overall health of flying-foxes if other food sources are not available. This highlights the necessity of providing a diverse landscape in order for flying-foxes to meet their nutritional demands worldwide.

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1. Nelson SL, Miller MA, Heske EJ, et al. Nutritional Consequences of a Change in Diet from Native to Agricultural Fruits for the Samoan Fruit Bat. Ecography 2000;23:393-401.

2. Dempsey JL. Fruit Bats: Nutrition and Dietary Husbandry. Nutrition Advisory Group Handbook Fact Sheet 014, 2004.