Bird Predators and a Mouse Plague by J

62 HAYWARD and MACFARLANE [ Bird Watcher Bird Predators and a Mouse Plague By J. L. HAYWARD, Wood Wood, and N. MACFARLANE, Kooloonong, Victoria During the summer and autumn of 1970 large areas of north western Victoria suffered a severe mouse plague. Factors contributing to this plague included the exceptional autumn rains of 1969, the heavy growth of pastures and self-sown wheat, and the generally mild conditions throughout winter and summer. In addition heavy grain harvests and the introduction of wheat quotas meant that great quantities of wheat and oats were stored on farms, providing an assured food supply for the mice. These and other factors enabled mice to build up in numbers throughout 1969, culminating in a population explosion in the new year. The abundance of food kept this population at plague level until well into winter. The observations recorded in this article were made in districts between Nyah and Boundary Bend, north-west of Swan Hill in the Victorian Eastern Mallee, and within twenty miles of the Murray River. All this area was profoundly affected by the mouse plague. The authors are engaged in agriculture, and have nad ctmple opportunity to observe the plague and note the actions of bird predators in relation to it. It has been suggested to us that our observations and comments in this case are worth recording. We, therefore, offer the following notes and briefly attempt to relate them to both the " normal" situation, and the plague situation, without trying to draw too many inferences. DIURNAL BIRDS OF PREY Generally, the Falconiformes are well represented in this district in terms of species, some as permanent residents and others as seasonal or irregular visitors. However, during the latter half of 1969 and the first half of 1970 there was a marked increase in the population of many regular species, and an influx of the much less common visitors. There was a very successful breeding of several species. In total this has meant an unusually great abundance of Falconiformes during the period of the mouse plague. Following are some details about all the species that are found in our study area. Black-shouldered Kite, Elanus notatus. A rather rare and sporadic visitor to all areas, this species built up to a very large population. This was due in part to a notably successful breeding season in 1969. The Kites then remained until May 1970, before numbers tapered off, though at the time of writing (August) many may still be seen on trees and power lines along the highway. Up to twenty birds were recorded around a farm at Piangil from as early as spring 1969, until June 1970. There were at least July ] Bird Predators and Mice 63 1971 five nests on this property. Some families appeared to stay to gether in parties for a long time. These birds were definitely taking mice, and we feel the extremely high population is directly attributable to the mouse plague. Oddly enough, Macfarlane did not record a single specimen in the Kooloonong district during this period. These kites were often noticed around wheat silos, where mice were, of course, prevalent. Letter-winged Kite, Elanus scriptus. Very rare; only one defin ite record for the area, made during 1969. Fork-tailed Kite, Milvus migrans. Rare, though for some years a colony has been established around saleyards and abbattoirs on the Swan Hill fiats. Breeding has not been recorded. Three birds were observed taking dead mice and other carrion from the Murray Valley Highway near Swan Hill. This was at daybreak during early March 1970. Six birds appeared over a stubble fire on this property in late March. Whistling Eagle, Haliastur sphenurus. A common resident throughout the district. It was generally felt that numbers and distribution of this species varied little if at all from the norm. J. L. Hayward reported 40 to 50 birds about the Wakool Junction early in May 1970. They were recorded as taking mice on occas ion, often in the form of carcases. Grey Goshawk, Accipiter novaehollandiae. One specimen of the white phase was present at the Wakool Junction for several weeks in April and May 1970. It was seen regularly perched on overhead sprays in an orange grove. Though not actually seen to take mice this bird, and other hawks, spent much time quartering a cante loupe patch heavily infested with mice. This is the only district record of this species. Australian Goshawk, Accipiter fasciatus. Not uncommon near the Murray River in normal years, but rare in the mallee. Rather more noticeable in the latter areas during the period of the plague, possibly due to river-based birds hunting further from their usual areas. Observed to take mice from around sheds at a Narrung orange grove. Collared Sparrowhawk, Accipiter cirrocephalus. Rare, but widely scattered throughout the survey area. The general impression was of little change in incidence. One bird frequented open oat silos at Kooloonong, which were badly infested with mice. It became very bold and not easily disturbed. It was not actually seen to take mice or birds, though making flying passes at birds varying from Red-backed Parrots to Ravens: Possibly birds, rather than mice attracted it to the vicinity of the silos. It was small, no doubt a male, and appeared to be just emerging from juvenile plumage. This was during the autumn months. Little Eagle, Hieraaetus morphnoides. Rare, but a regular resi dent, rather more common near the Murray. Most observers noted no difference, though M. Irvin recorded that one specimen appeared about 10 a.m. each day where swarms of mice were 64 HAYWARD and MACFARLANE [ Bird Watcher feeding in broad daylight around temporary silos. The Little Eagle proceeded to quarrel with the numerous Ravens and Kestrels present, though without appearing to take a great deal of interest in the mice. This was towards the end of the plague. Wedge-tailed Eagle, Aquila audax. Regularly seen in rather small and variable numbers. No change was noted in occurrence, which is probably only to be expected. White-breasted Sea-Eagle, T-ialiaeetus leucogaster. A very rare resident along the Murray River. No observations related to the mouse plague. Spotted Harrier, Circus assimilis. Rare, though regular visitor. Present in somewhat greater numbers during the latter part of 1969, when breeding records were made. Numbers reached a peak about February-March 1970, when this species was much more abundant than usual, particularly in the north of the survey area. The greatest number coincided with the rapid build-up in mouse numbers, though quail were also plentiful at this time. One bird was several times recorded working about grain silos at a rail-siding. Some, including juveniles, were present throughout the winter of 1970, a season when they are not normally recorded here. They were frequently seen to take mice. Swamp-Harrier, Circus approximans. Normally quite frequent along the Murray River, in irrigated areas, and within a few miles of the river. A number of birds were noted well out in mallee areas between November 1969, and May 1970. One was disturbed from the ground west of Kooloonong and about fifteen miles from the river, in an area where it had not previously been recorded. They were seen to take mice and one bird spent much time around wheat silos at Miralie. They were also common around grapevines at Nyah West, where mice were plentiful, but left when the mice disappeared. Black Falcon, Falco subniger. Rare and sporadic visitor. Some observers noted no difference in incidence, though others recorded it rather more frequently than usual. This may have been partly due to keener watching. Seen often in the Kooloonong district, once or twice in proximity to the Brown Falcon, which afforded a good opportunity for comparison. They were seen to fly in over the top of a tractor to take mice disturbed by cultivating operations. Peregrine Falcon, Falco peregrinus. Rare and sporadic through out the district. No apparent change in incidence. Little Falcon, Falco longipennis. Very rare and confined mainly to the near river areas. Most observers noted no change in numbers or habits. However, R. Storey considered these falcons to be more common than usual. He once recorded four or five in one day along the railway line south of Nyah West. He also saw this species take mice. Grey Falcon, Falco hypoleucos. Very rare at all times. One or two likely sightings were made in the Kooloonong area, where a bird which may have been of this species was reported harassing fowls in a closed pen. July ] Bird Predators and Mice 65 1971 Nankeen Kestrel, Falco cenchroides. Another common resident which also underwent an extensive population increase. Hundreds were to be seen on trees, fence posts and power lines, during late 1969 and 1970. They are still numerous (August) and preying on mice, though their numbers are now far below the peak. The population throughout the survey area has not been higher within recall, and in places almost every fence post bore remains of their repasts, in the form of bones, skin and entrails. It would appear that they deliberately avoid eating portions of the latter, chiefly the stomach and intestines. Kestrels frequented silos and farm buildings, on a permanent basis until the plague died down. The Kestrels also bred successfully in 1969. Brown Hawk, Falco berigora. Normally a common resident, this species bred successfully in 1969, and numbers were considerably higher than usual throughout the period of the plague. A heavy influx occurred in late May 1970, and as many as one hundred birds were reported within a mile radius of Piangil, during June July.

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