Aust. Bird conference talk - 2010
The following article is a summary of the recent talk given by Ken and Jenny Hodge at the Australian Bird Conference in N.S.W.
SEA EAGLES of GIPPSLAND UNMASKED – REMOVING THE THREATS TO A THREATENED SPECIES
MAN V WILD
We are writers, teachers and photographers. In 2005 we commenced a 10 year study of the nesting sustainability of sea eagles in the Gippsland Lakes. Our study area encompasses 400 square klms. of the Gippsland lakes and coastal region from Sale to Metung and includes 3 main lakes, some minor lakes, rivers and morasses as well as sections of the ninety mile beach. We are currently monitoring 20 nests with a focus study being done on the sea eagle pairs residing in Lakes National Park and a book on Australian sea eagles is well underway.
The joys and tragedies of photographing sea eagles in Gippsland are many but most of all you must be diligently passionate in all terrains, acquire a love of mosquitoes and be prepared to get very wet on many occasions!
DIFFERENT BY NATURE
Sea eagle sexual dimorphism is usually obvious with size being the main difference. The female is typically much larger and as they age, both acquire a black stripe at the back of the eye. There are other significant behavioural idiosyncrasies both at rest, hunting and at the nest. Some differences include resting period discrepancies, the female spending habitually longer periods resting than the male outside of nesting time, nesting territories being retained by the female more than the male, hunting behaviours which include slower female wing pace and differences in vocalisation with the females’ honking being both slower and sonorous in note.
When the female of our detailed study took on a new partner directly after the collapse of her nest in 2008, we were able to record the male’s plumage colouration change over a 1 year period. They did not rebuild the nest for one year possibly due to his immaturity. Within a year he had lost all brown juvenile markings and went through a strong moult period to gain his adult white and grey feathers. In the following February we recorded some spectacular mating behaviour and a new nest was finished in a 3 week period in late May this year.
RAISING A FAMILY
A typical sea eagle nest is built within sight of permanent water in the most dominant tree, which is re-used and can reach over 2 metres in height and diameter. Sometimes tree selection can be an exotic such as radiata pine species. In the area in our study where there was no obvious dominant tree we undertook a survey of trunk diameter to determine if the eagles were selecting a tree based on structural stability. Trees selected for nests had trunk diameters in the top 20%. Approximately 85% of nests in our study are built in vertical forks of 2 to 3 branches, whilst the remainder are built on horizontal forks, the lowest being only 15 metres from the ground. Size of nests is dependant on availability of nesting material and we observed very small nests in dead remnant eucalypts on farm properties in contrast to the large nests found in National Parks. One pair in our Park own 4 nests.
The requirement that sea eagles have for a zone that is free from human interference made us query the ethics of photographing chicks in the nest that has been done in the past.
Some statistics about the freshly dropped sticks collected from beneath the new nest built in 2010 are:
From our study we have researched the times of egg laying and found they can vary from season to season by as much as 20 days but surprisingly, all adjacent nesting eagle pairs in the Park still lay within days of each other despite seasonal date disparities
Sea eagles are proficient hunters in the Gippsland area and we have witnessed them taking a wide selection of prey, including -
· Bird species ( swan cygnets, Hard-head duck, shearwaters, grebes, cormorants, fairy penguins)
· Mammals ( possums, bats, gliders)
· Aquatic (eels, bream, mullet, carp)
· General carrion
Juveniles still on the nest are fed meticulously and regularly by parents for the 12 week phase and part of our current study is to record the load of prey an adult eagle can lift. We became aware very early in the study that fishermen in the lakes had been feeding sea eagles for over 20 years and contact with these fishermen has been invaluable. The ones we know take a significant interest in the birds and are quick to offer help for the sake of eagle preservation.
TOO PRECIOUS TO LOSE
As coastal real estate is appreciated in the Gippsland Lakes, one of the greatest threats to the birds is loss of habitat caused by human encroachment.
The majority of nesting territories in the lakes area are vulnerable to even small increases in sea level rise, with the hinterland being cleared farm land with few suitable nesting habitats.
Educating the public involves sharing information and creating interest and our regular feature articles on the sea eagles in the Gippsland Times aid this. As suitable remnant nest trees expire over time, new ones take years to attain necessary height and populations of people increase, the optimum habitat for sea eagles is always going to be in a delicate equilibrium, with no real guarantee of success without active involvement and awareness. With this in mind, in 2010 we formed a new association called S.E.A. E.A.G.L.E. (Sea Eagle Awareness Educational Association for the Gippsland Lakes and Environs) which we hope will allow a greater level of communication with the general public and will assist us in the study.
Around Loch Sport in November we ran into a diversity of wildlife – so much that we thought we would share the photos with you. The female sea eagle, intensely hunting for her young, missed out on a black swan cygnet lunch but unfortunately the male eagle was devouring one as we arrived. A koala wandered down Christopher Crt and dolphins often accompanied our boat on eagle studies, relishing in the gentle churn and froth it created. When all is said and done, we dwell in a paradise that must be preserved at all costs. Jenny and Ken Hodge Contact: email@example.com