4. RESULTS & DISCUSSION   continued

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4.3 Peregrine elevation cut-out   continued

4.3.2.3 Peregrines' reliance on medium to long-range visibility: As stated above, it is suggested that cloud inversion is the key to peregrines nesting cut-outs in KNP. The reasons are felt to be related to the peregrines' strong dependence on its medium and long-range visibility. In particular it relies on this medium and long-range visibility for the following: a) Defence of the nest Defence of the nest is one of the outstanding features of peregrines. Their eyesight is so keen that it is rare for an intruder not to be seen nearing a nest site. Cloud inversion would inhibit the peregines' most powerful sense. If eyesight is relied on for defence of a nest, and an intruder cannot be seen nearing a nest, then the bird is vulnerable. b) Food exchange Peregrines rely on their eyesight for food exchange whilst incubating and when they have young. Initial contact can be by hearing a mate calling on his/her way in but eyesight is the key for this exchange. Cloud inversion would impair this basic daily occurrence. c) Hunting close to the eyrie Once young are old enough to be left alone, the female will begin to hunt close to the eyrie. She definitely needs clear unobstructed views to do this as well as being able to see the eyrie in order to defend it. It is extremely difficult to get near an eyrie when the young are approximately 10-20 days old because of the female placing herself in a position with a commanding view of the area. Once the young get older, it is easier to approach an eyrie unnoticed probably because the female is hunting further from the nest. The amount of days with cloud inversion in KNP above 1300m would certainly create difficulties for this bird of prey to inhabit this zone. In terms of consecutive days of cloud inversion (generally 3-7 days), survival for a bird such as the peregrine would be almost impossible due to its need to feed daily. It is interesting to mention that the little falcon, which is not unlike the peregrine in terms of hunting technique and use of speed and planned attacks on prey over large distances, also appears to be absent above 1300m. In summary, the weather statistics support the suggestion that cloud inversion is the key to determining the elevation cut-out for breeding peregrines. There is also some anecdotal evidence to support this suggestion. 4.3.2.4 Personal observations: It is not known whether peregrines maintain their home range all year. Observations of cloud inversion at their eyrie would support the theory of cloud inversion determining the cut-out level for peregrine breeding. It should be noted that the micro-climate of each valley system will dictate the level of inversion at a given time. The base of the cliff is approximately 850m and the cliff extends to just over 1200m. Most instances of cloud inversion, particularly during winter, are at around 950-1000m. The eyrie on this cliff, the same one used for the past four years of the study, is just under 950m and is generally exposed. This cliff has many available ledges at higher levels but during the period of this study they were not used. It is suggested that the reason is the cloud inversion level on this cliff. Surveying site 28 during September 1999, involved camping overnight at the summit of a hill (at 1450m). In the morning there was an inversion in which visibility was only 20-30m. After descending through the fog, the cliff, which is a very extensive cliff, was surveyed for eyries. The inversion had dissipated by the time a previously used ledge at approximately 1300m was located. This was very close to the inversion level base earlier that morning. This cliff has potential for an excellent eyrie higher than the actual nest site, but it is not used. It may be that these instances of different levels of inversion show how each cliff can be affected altitudinally by their own micro-climates. It is suggested that the number of days with cloud inversion in areas beyond 1300m may be too many for peregrines to occupy. This 1300m level may very well be the altitudinal cut out for peregrines in Australia. At Happy Jacks there is a suitable quarry with good ledges and vertical faces that should attract peregrines to breed. This quarry faces north which is a good aspect. Very little human disturbance would occur in and around this quarry as this is a restricted area and all tracks into the quarry have been closed. The altitude of the quarry is 1400m. There is also a very good natural cliff not far away. During this study, peregrines have not been observed in the area, nor have any peregrine casts been collected at the quarry. A large number of kestrel casts however, have been collected at the quarry. It should be noted that, unlike the peregrine, the kestrel hunts close to the ground, often using trees as its vantage point. The kestrel's hunting technique is not impeded by fog to the extent that the peregrine is impeded.