What do Gang-gangs eat?

Thanks you to all those that contributed records to the Gang-gang diet study. A summary of the findings is provided below. The full report can be read and accessed at the bottom of this page

http://redhillregenerators.org.au/?page_id=277

In summary, 4135 Gang-gang Cockatoo feeding records were collated from image-based records posted on social media and citizen science platforms and from written records of bird observer clubs and bird group databases. The records covered the whole Gang-gang range but were clustered in and around the larger urban centres, particularly Canberra and Melbourne.

There were 275 food items recorded in the 16,798 feeding events. A feeding event being the number of Gang-gangs in an image or written record multiplied by the number of days over which the feeding event was recorded. Three taxa, Blue Gum Eucalyptus globulus, Hawthorn Crataegus sp. and Liquidamber Liquidambar styraciflua comprise a third of all recorded feeding events. The top twelve taxa account for 54% of all feeding events. Over half of the food items were recorded as being eaten only once or twice amongst the total record. Gang-gangs sample a wide range of foods, and have a varied diet, but the bulk of their observed feeding was on a few taxa.

Of the plant species eaten 26% are exotic, which suggests Gang-gangs have adaptability to new food sources. Targeted or main food species vary across regions and seem to be related to availability and a degree of preference. For example non-local Blue Gums comprise 58% of the eucalypt feeding records in Canberra, but other eucalypts that Gang-gangs feed on are much more numerous in surrounding bushland and similar in number re amount of planting. The Gang-gang diet is varied and food is abundant, and the Gang-gang adapts to what is available. It seems unlikely that food availability is a limiting factor for this species.

Gang-gangs eat from seven main food groups. These are, in terms of the proportions that they constitute to the recorded feeding events:
• eucalypt gum nuts and flowers (43%);
• berries with relatively large seeds but small fruits (21%);
• green cones of mainly the Pinaceae and Cupressaceae families (10%);
• wattles, almost exclusively in spring – early summer and on plants with green pods (8%);
• soft pods from a variety of tree and shrub species, but mainly Liquidamber (7%);
• nuts mainly walnuts Juglans sp. and oak Quercus sp. (3%);
• and invertebrates mainly sawfly and lerps (1%).

Eating from the range of food groups seems to be of importance. Amongst the ten most fed-on taxa all of the first five of the above food groups are included.

Wattles are the main food item in November and December. Wattles remain a major food item in January but exotic berries become the main food item through February and March. Gum nuts and flowers are the major food item from April to October. They peak as the major proportion of the total diet from May to August.

A recognisable crest-damaged male Gang-gang feeding two chicks in a nest in Canberra bushland was observed foraging 3.9km from the nest as well as three other closer locations. He repeatedly fed on Sunflower Helianthus annuus seed at one location. This may be of concern as overfeeding on Sunflowers by caged Gang-gangs can lead to infertility and other health problems.

Feeding records, during the September – January breeding season and within 4km of any one of 49 known nest trees in the Canberra area, were found to have a greater proportion of gum nut/flower feeding events, and less wattle feeding than those recorded more than 4km away from known nests.

The Gang-gang diet differs across its range and this seems to largely reflect the food species that are available locally (both planted or indigenous to certain areas). However there also appear to be some cultural differences between populations with some widespread species such as Water Milfoil Myriophyllum sp., Dogwoods Cornus sp. or White Poplar Populus alba only being eaten or predominately so in one bioregion.

Collection bias limits comparisons being made between tall forests (where few records were obtained) and urban and peri-urban woodland and dry forest habitats (where the bulk of records were obtained). However, the data demonstrates that the latter habitats are important for foraging and breeding Gang-gangs. These habitats also support the vast majority of currently known nest trees.

Thank you.

Anotado por michaelmulvaney michaelmulvaney, 21 de julio de 2022 a las 09:25 PM

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