A short note on a beetle infestation of a Little Eagle nest

A recently published paper on the possible effect of a beetle infestation of a Little Eagle nest and the eagles' behaviour.

Rae. S., Roberts, D. and Olsen, P. (2023). Abandonment by Little Eagles Hieraaetus morphnoides of a nest infested with beetles. Australian Field Ornithology 40: 17-19. (pdf copy)

Abstract. A pair of Little Eagles Hieraaetus morphnoides in the Australian Capital Territory was recorded (on closed-circuit camera) feeding and mating on a nest and had added a layer of green pine sprigs in preparation for egg-laying. Many beetles, likely a species of Dermestidae, were recorded in the nest during the time that the birds were there. The eagles abandoned the nest and moved to another 1.7 km away, where they laid a clutch. It is possible that the beetle infestation was the cause of abandonment.

To watch the video recording of the beetles emerging, follow the link embedded in the PDF copy of the article.

The male Little Eagle with food on the nest.

Scores of Dermestidae beetles were filmed emerging from the eagle nest, indicative that there had been as many larvae within the nest while the eagles were preparing the nest for laying eggs in the springtime. The eagles added a considerable amount of pine sprigs to the nest lining before abandoning the nest, to lay in another nest within their home range. Both these behaviour acts are typical of birds' responses to avoiding disturbance from beetle larvae. The paper is provided as a note to illustrate this behaviour, which is probably under-recorded. The evidence in this case was only recorded opportunistically as the nest was under constant surveyance with a nest camera.

The eagle pair mating on the nest prior to abandoning it.

The fifth annual report on the study of Little Eagle breeding in the ACT, 2021

A particularly dark fledgling Litte Eagle, the offspring of two dark phase parents.

THE BREEDING SUCCESS AND DIET OF LITTLE EAGLES IN THE ACT AND NEARBY NSW IN A WET YEAR, 2021

Rae., S., Brawata, R., Wimpenny C., Stol, J., Roberts, D., Mulvany, M., davies. M. and Olsen, P. (2022). The breeding success and diet of Little Eagles in hrte ACT and nearby NSW in a wet year, 2021. Canberra Bird Notes 47: 81-87. (pdf copy)

Abstract. Monitoring of Little Eagles (Hieraaetus morphnoides) breeding in the Australian Capital Territory in 2021 was impaired by COVID-19 restrictions. It was a wet year. September and November, when most eagles lay eggs and hatch young, were notably wet. Six Little Eagle territories were recorded in the ACT in 2021. There were at least five pairs with nests, and a lone male was recorded at a sixth nest. All pairs laid eggs and one failed during incubation. The chicks in three nests died during periods of prolonged heavy rainfall and one pair raised a chick to fledging. In NSW, three pairs raised a single chick each. A known nest was built up in another territory in NSW but no birds were observed at it. The overall number of chicks reared per pair was 0.50. The proportion of rabbits in the birds’ diet was low compared with the three previous years. How weather and diet might affect the breeding success of Little Eagles are discussed.

The remains of a fledgling Little Eagle that died when a severe hail storm passed over the nest area. The partly scavenged body lay directly below the nest.

The wet weather continued in 2021 with mixed effects on the Little Eagles. All known pairs laid eggs which is indicative of a good food supply. Although rabbits were abundant, fewer were eaten by the eagles, perhaps because they had less access to them due to the prolific growth of tall grass and weeds, particularly thistles. The tall sward of dried thistle stalks from the previous year were thickened by fresh growth in 2021, presenting a formidable barrier to an eagle trying to dive after any terrestrial prey. The diet was supported by a higher proportion of birds than in the three previous years, so food was not likely a cause for breeding failure. Rather, severe storms with strong winds and high rainfall were more likely the main cause of breeding failure. This was supported by the remains of two chicks found below their nests and another that disappeared, all after storms. The direct and indirect effects of high winds and rain will be monitored in future years. 

Over three years of movement data from one bird

This is V4, the Little Eagle who features on the masthead of the Little Eagle Research Group facebook page. The antenna of her gps-tag can just be seen in that photo, protruding behind her. She has now dropped her tag as can be seen here, as she sits in a tree above where the tag was found today.

The habitat was a bit overgrown after three rainy years, with tall thick shrubs, and tall grasses and forbs beneath.

The tag was tricky to see, lying amongst the grass and leaf litter.

The tag (made by GeoTrak Inc.) is about 6 cm long, with a 20 cm antenna, and painted eagle brown to blend in with bird's plumage.

Fortunately, the tag was still sending out its position via satellite, so we could read the coordinates of where it was lying and find it quite quickly depsite the terrain.

The tag was fitted with a teflon harness, like the straps of a backpack. A weak link of cotton thread joined all four straps at the breast, and this was designed to break after a period of time. 

The thread broke three years and five months after deployment, perfectly timed as the device was still running, but we do not expect it to last much longer. In that time, data from four breeding and three wintering seasons have been downloaded, a wealth of information. The bird spent all that time within the Australian Capital Territory, spending each non-breeding period in the same area about 20 km from where she was first caught and tagged, and about 10 km from her current nest site.

She has done well and we wish her all the best. 

Thank you for the data lovely bird.

 A short note on Little Eagles.

This article was recently published in Boobook, the newsletter of the Birdlife Australia Raptor Group. It gives a brief description of some movements by a few eagles between nest sites.

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If you like this article or would like to keep up with other raptor research in Australia, why not consider joining the Birdlife Australia Raptor Group. Go to the Birdlife Australia webpage and follow the links.