Vol. 7 March, 1978 No.5

Observations on Peregrine Falcons Nesting in W erribee Gorge, Victoria.

By BRYAN P. WALSH, National Park Ranger, Werribee Gorge Park, C/o N a tiona[ Parks Service, Ministry for Conservation,

240 Victoria Parade, East Melbourne, Victoria, 3002.

In June, 1974, the National Parks Service assumed management of the Werribee Gorge. Soon after, surveys of the flora and fauna were conducted to ascertain the Park's natural assets and to assist in drafting a management plan. Results of the fauna survey and discussions with local naturalists indicated that both Peregrine Falcons and Wedge-tailed Eagles had nested or attempted to nest in the Park for many years. Apparently the eggs and chicKS of both species had been subjected to human interference during most years.

The National Parks Service considered that the Peregrine Fal­cons were a valuable asset of the Park and that they deserved special protection in the form of a constant watch being imple­mented by the Park Rangers. It was also an excellent opportunity to take detailed notes and to assist the Fisheries and Wildlife Division in their State-wide study of the Peregrine Falcon.

In conjunction with routine park duties, an eight-hour daily watch was kept until egg laying, and then the programme was stepped-up to ten hours a day until cessation of observation. Observations were conducted from a hide on the opposite side of the Gorge to the Peregrines' eyrie, a distance of some 120 metres. A Yasco Spotting-Scope was used for detailed nesting studies, and a pair of 7 x 50 Zeiss b inoculars for in-flight activities.

To eliminate disturbance on the rock faces where the Peregrines were selecting their nest site, rock-climbing was banned from August 1, until November 30, 1976; hiking was also banned in the immediate vicinity of the cliff faces. Cooperation by the public was good and few violations of the ban were detected.

138 WALSH

Extract of Notes Taken During Nesting in 1976: August 3:

[ Bird Watcher

By this date the Peregrines were still alternating between two sites, Falcons Lookout and Daintrees Cliff, spending long periods perched on the cliff faces. A Wedge-tailed Eagle's nest in a tree half-way down Daintrees Cliff was freshly lined with eucalypt leaves, and W'f wondered whether their presence might eliminate Daintrees Cliff as a possible site for the Peregrines. August 4:

The Wedge-tailed female was sitting on the nest at Daintrees, but the Peregrines continued their alternate perching on the two cliffs as usual. August 9:

By this time the Peregrines were starting to show a preference for Daintrees Cliff, despite the fact that the Wedge-tailed Eagles had two eggs and had started incubation. August 11:

It was now apparent that Daintrees Cliff was the Peregrines selected site; they were spending most of their time on or around the cliff. August 15:

T he male Peregrine flew down to an eyrie site on Daintrees Cliff, and, judging by the lime coating, it was probably a nest used in previous years. It was a natural wind-eroded cave approxi­mately 2 m wide at the base tapering to the top which was approximately 1.5 m high. It was approximately 0.7 m deep with a natural vessel-shaped floor. The male stood on the edge of this site, lowered its head and made a cackling noise quite distinct from any previous call and resembling "skir-ka, skir-ka, skir-ka". We called this nest site Number One. August 16:

T his inspection and cackling process was repeated by both birds, but mainly the male, until August 16 when the female flew to another site (1.3 x 1.0 x 0.5 m in size) further along the cliff. There was no lime wash evident, the floor of this site sloped slightly forward and to one side, and it had obviously not been used in recent years, if ever. This site was called Number Two. August 16:

From this day untill September 1, both adults repeatedly flew into their respective chosen eyrie sites, the male into No. One exclusively, and the female into No. Two exclusively, lowering their heads and making the usual "skir-ka, skir-ka, skir-ka" call. From a human viewpoint No. One site was preferable; it was naturally cup-shaped to prevent eggs or chicks from rolling out, and offered shade. The No. Two site was exposed, did not offer shade, and had a precarious floor. September 1:

On this day both birds flew to their respective sites and began cackling. After some ten seconds the male suddenly flew to site No. Two for the first time and joined the female; they both walked

March 1978 ] Peregrine Falcons nesting 139

inside, lowered their heads together until they were touching and made a "chip-chip-chip" call over what was finally the selected site. The feathers of the female were slightly ruffled and she appeared to be submissive ; the male then took off; leaving the female alone in the eyrie. She lowered herself onto her haunches in a sitting position, fluffed her feathers as if having a dust bath, got up and flew off and joined the male. This "excavation" process was repeated daily until a nest cup was completed on approxi­mately September 21. Each excavation lasted about 3 or 4 seconds, so metimes two or three times a day, occasionally using talons to scrape backwards like a fowl. In the final stages the female would sit in the cup and, with her mandible, scrape stones towards the cup edge. September 24:

An egg was laid ; through the spotting-scope the egg looked well-marked and intact. In the ensuing few days the female was very erratic with her periods of incubation, varying from a total of 3 to 4 hours a day, and made up of 10 to 40 minute periods. The male was acting normally, taking up 8entry duty on the cliff face, hunting to support the female , and took hi s first turn at incubation on September 25.

It is unknown whether incubation was carried out at night. On some occasions when watch fi nished at dusk, the female would still be on the egg; on other occasions the egg would be unattended. At fi rst it was thought that the Falcon would settle down once a complete clutch had been laid, but September 26 came and pas8ed without another egg. The female looked unsettled, and continued her short periods of incubation , with the male alter­nating and appearing to do his best to get her to sit on the nest. October 3:

The Peregrines re-commenced flying about in a pair, some incubation was still taking place, but highly irregular and still only one egg; it was thought that this day may have marked the commencement of loss of interest in the egg. October 5:

Although the male was still doing most of the hunting, they hunted as a pair for the first time since eyrie selection; the incu­bation pattern was still irregular. October 7:

Incubation periods be::oming shorter, only one to two hours per day, and made up of 5 to 20 minute intervals. October 8:

Total incubation period for the day was 30 minutes by the female; this was the last time she sat on the egg. October 11:

Only 5 minutes incubation recorded for the whole day; the last time the male sat on the egg. October 12:

The male flew to the eyrie, looked at the female who was gliding past the cliff face and made the "chirp, chirp, chirp" call as

140 WALSH [ Bird Watcher

if enticing her to return to the egg. The female had lost all interest, and the male flew off to join her. No incubation this day - eyrie was abandoned. October 13:

Watched the eyrie all day, with the Peregrines only passing over the cliff once during that period. After consultation between the National Parks Service and Fisheries and Wildlife Division, the egg w~ collected for chemical analysis.

Interactions With Other Birds of Prey: The site chosen by the Peregrines was surrounded by other

birds of prey. Wedge-tailed Eagles nested a mere 70 m further along the cliff, while in the forested area on top of the cliff was a pair of nesting Brown Goshawks, and opposite the cliff was a pair of nesting Brown Falcons. Frequently other birds of prey such as Black-shouldered Kites, Whistling Kites and Nankeen Kestrels also flew over the area.

In the early stages, the Peregrines were very aggressive, par­ticularly towards the Wedge-tailed Eagles; they would stoop on the eagles at an unbelievable speed, as well as attack from below, until finally it appeared that territory boundaries were determined and, provided the Wedge-tails did not glide below the tree crowns on top of the cliff, or fly past the eyrie face, they were not attacked.

The only other bird of prey that was attacked was the Brown Falcon, but even in this case the Peregrines were not consistent and territory boundaries were impossible to define. The Brown Goshawk was given more liberties in its approach to the eyrie than any of the other birds of prey and was never attacked. (A comical sidenote was provided by Welcome Swallows which were nesting in adjoining caves; they often attacked the Peregrines . when they glided past their nest sites.)

Displays: Both Peregrines relished a calm sunny day, and I looked forward

to observing them under such conditions. On such a day they would effortlessly spiral on a thermal until both were mere specks in the sky through a pair of 7 x 50 binoculars. At an altitude of 400-500 metres, first one bird, and then the other would fold its wings flat to its body and plummet earthwards at an oblique angle at such an incredible speed that it was difficult to follow them with binoculars. As they came into focus, it was possible to see that these magnificent stoops were controlled by the wing ~boulders which were opened from the body by 30 to 50 mm with the primaries still hard against the bird's body. Not until what seemed to be the last moment did the birds spread their wings to rise in an arc and gently land on a dead tree or rocky outcrop.

Another noteworthy display was during eyrie site selection. The female was gliding up the Gorge and the male was at nest site No. One; he took off and flew approximately 10m in front of the female, suddenly he executed an amazing backwards tumble, tumbling vertically downwards for at least 7 m before pulling out

March 1978 ] Peregrine Falcons nesting 141

into a glide and flying back to his preferred site. In appearance the tumble was identical with that of a tumbler pigeon. Hunting:

Most hunting was done by the male, although occasionally they would hunt in pairs. Two incidents of co-operative hunting were of note. The first involved a female Golden Whistler perched in the top of a dead tree. Both Peregrines flew one behind the other towards the bird, spaced about 7 m. apart, the male flashed past the unsuspecting Whistler and let out an alarm call. The Whistler immediately was airborne only to be hit from behind by the following female. The second occasion involved a small flock of Black-faced Cuckoo-shrikes flying over some trees; they sighted the Peregrines and immediately dived into the trees. One Peregrine remained aloft whilst the other flew in under the canopy to try to flush a victim; it then flew up above the tree tops, whilst the other flew in amongst the trees. This created a circular motion which was repeated approximately six times until a Cuckoo-shrike panicked and a kill was made aloft.

Many prey exchanges were witnessed during observations. Usually the male would fly off hunting between 8 and 9.30 a.m., rarely did a hunting excursion last more than thirty minutes. He would return up the Gorge with the prey clutched in his talons making a rather plaintive drawn-out "chirrup, chirrup." Suddenly the female would appear making a similar call; she would fly up behind, and underneath the male, swinging her talons forward and upwards until their feet touched and prey was exchanged. She would be momentarily flat on her back with legs stretched upwards, and the male would be looking and reaching downwards. Only on one occasion was the prey dropped in such an exchange, and it was stooped upon and re-grasped by the male before it had fallen 7m. ·

The diet of these birds during the observation appeared to be mainly introduced Starlings and Sparrows. Conclusion:

Despite the disappointing ending, the observation was regarded as a success, as the information gained will assist the Fisheries and Wildlife Division in its efforts to gain an overall picture of this magnificent bird in this State.

I will not speculate here on the reasons for the dis-inclination of the female to incubate, but such behaviour may be explained in forth-coming papers by experts now working with the Fisheries and Wildlife Division.

From the National Parks · Services point of view, we were successful in enabling the birds to carry out their breeding pro­gramme (albeit unsuccessful) without human interference, and in fact we apprehended youths attempting to steal the Wedge-tailed Eagle eggs. The Wedge-tails have since successfully been hatched and reared. The knowledge gained will help us in the implemen­tation of management plans to assist in the protection of the Park's natural inhabitants, particularly the birds of prey.

142 SEDGWICK

Acknowledgements: I would like to acknowledge the assistance given by:

[ Bird Watche r

Mr. W. Emison and Mr. W. Bren (Fisheries and Wildlife Division), Dr. C. White, for help with observation technique, My fellow observers from the National Parks Service: Mr. F. Lobb,

Mr. M. Kewish and Mr. J. Myers, and Mr. D. Saunders (National Parks Service) for editing the paper.

Historical Bird List: Open Forest at Larrimah, Northern Territory, 1944

By ERIC H. SEDGWICK, 20 Herbert Road, Harvey, W.A., 6220.

During a sojourn at a military camp six miles north of Larrimah, Northern Territory, in 1944, I kept careful note of all species of birds encountered in the course of twelve 3.2 km. transects through typical open forest of this region (16° 30'S; 132° 30' E. approx.).

Specimens of many of the dominant plants of this area were collected and these plants are listed in "Northern Territory Bird Notes" . Emu 48: 295 .

This survey was utilized in compiling the paper mentioned above, but as the avifauna of this area is still relatively little known, the data is now presented in detail.

The data reflects the wealth of bird life in this area: the large number of species present in a homogenous habitat - 65 - and the large number of individuals which may be inferred from the high frequency with which about one third of these was en­countered.

In this type of country Black-fronted Dotterels appear beside small temporary pools which occur when heavy rain falls.

Species of less than 8% frequency were recorded in the study area between January and October 1944, but not in the course of any of the twelve transects.

* = Migrant: Should be admitted to higher percentage group.

Names used follow the R.A.O.U.: "Checklist of the Birds of Australia" Pt. 1-Condon, H. T. 1975. and "Interim List of Australian Songbirds"- Schodde, R. 1975.