September ] CHISHOLM, Cuckoos are very Resolute 49 1973 Cuckoos Are Very Resolute By A. H. CHISHOLM, Sydney Among many problems associated with parasitic birds in Aus­ tralia, some of the most provocative are presented by the Black­ eared Cuckoo, Mesocalius osculans. This species, the only member of its genus*, has a wide distribution, mainly throughout open forests inland; and yet, in contrast with various other cuckoos, it has very few fosterers, and in general it remains rare and relatively little known. Probably its status as an unfamiliar species is not due to modest colouring and size (having a length of about 7 inches, it is an inch or so longer than the common bronze cuckoos), but, rather, is the result of its furtive nature and Jack of assertive vocalism: it has a slender voice and does not appear to call with the usual cuckoo frequency. Its chief host is another distinctive species, the Speckled Warbler (Chthonicola), which, like the cuckoo, is largely a ground-feeder. It is also a ground-nester, its practice being to scrape a circular cavity in earth near debris or a grass-tuft and to build over it a neat fibrous structure with a side-entrance. The eggs, usually three, are uniform dull red, thus causing the bird to be given, in earlier days, the name of "blood tit", one of the very few labels of the kind (based on egg-colouring) to be applied to any bird anywhere. Very curiously, the egg of the Black-eared Cuckoo not only approximates the eggs of the much-smaller Speckled Warbler in size but closely resembles them in colour- this although no such safeguard would appear to be needed in a dark chamber- and, also curiously, whereas the red of the host's eggs is "fixed", that of the cuckoo's egg can be rubbed off by a damp finger, disclosing a pale blue. Apparently this "colour sense" on the part of the cuckoo, as well as its addiction to domed nests, persists in areas where the Speckled Warbler is not available. Thus the intrusive egg has occasionally been found to be foisted on the Redthroat and the Striated Field­ wren, both of them small birds which build domed nests on or near the ground and lay chocolate-coloured eggs. On the other hand, however, the reddish egg has sometimes, though very rarely, been discovered alongside eggs of contrasting colour, as in the case of a Blue Wren (in a nest built near the ground) and in the cases of the Yellow-rumped Thornhill and the White-browed Babbler (both tree-nests). Doubtless complete lack of favoured accommodation compelled the cuckoo, in these instances, to "break new ground". Yet, unlike some of its relatives, it has always remained faithful to nests having side-entrances to darkened chambers. Presence of the Black-eared Cuckoo's egg in the nest of a White­ browed Babbler was a surprising discovery made at Maryborough (Victoria) in November of 1968. Feeling two eggs in one of the *Because its field characteristics set it apart, I disagree with the suggestion that this species should be placed in the same genus as the bronze cuckoos. CHISHOLM [ Bird Watcher large stick structures, sited some 6 feet aloft in a eucalypt sapling, I removed them for examination - this merely because such eggs often show variants in their shades of purplish-brown- and was astonished to find that one of the pair was a product of the Black­ eared Cuckoo, which I had seen previously only in nests of the Speckled Warbler in forest areas near Melbourne and Sydney. What had caused this development? The cuckoo could not "know" that the Babbler's eggs, obscured in a deep chamber, bore a broad resemblance to its own egg. It had, seemingly, adopted this tree-sited nest simply as a matter of urgency, because it could not find any other domed nest on or near the ground. But would the young intruder, when newly hatched, be able to eject its companion from a chamber that had (as I found on examination) a ledge about 2 inches deep at the entrance? Earlier, at a spot near Sydney, I had seen an infant Black-ear, while still sightless and featherless, eject two nestling Speckled Warblers after a hard struggle, but in this latest case the task seemed almost impossible. Nevertheless the deed was done somehow. The actual operation was not seen, but a few days later I found a young Babbler dead on the ground and the blackish, gnome-like change­ ling flourishing alone in the nest. Retribution followed, however, for a few days later again the young cuckoo had vanished, presumably having been taken by some predator. Within the same week, in the same general area, another egg of the Black-eared Cuckoo was found in another nest of the White­ browed Babbler. Normally, the local man who reported this second find (Mr. E. Rich) would not have bothered to examine such a nest, the fact being that White-brows (unlike their once-common relatives the Grey-crowned Babblers) are still fairly common in the district. It seems possible, therefore, that some few similar intrusions by the Black-eared Cuckoo may have occurred earlier and passed undetected. At any rate, in the second instance noted robbery again occurred, for the cuckoo's egg and the babbler's egg as well disappeared before hatching. What predator was responsible in each instance remains a provoking problem- as indeed is the case with many other occurrences of the kind. An interesting sidelight on the general subject is that, at the relevant time, several examples of the Speckled Warbler, previously very seldom known anywhere in the district, were seen in the area where the intruding eggs were found in babblers' nests. Close searching, however, failed to reveal a nest of the little speckled bird. The thought arose therefore that although the cuckoo may have detected the presence of its favourite host, it too had failed to find a nest, possibly because the newcomers had not "settled in". At all events, renewed searching in a later springtime was more productive. It resulted in the finding, in separate areas, of two nests of the Speckled Warbler, the first of their kind known in the district. September ] Cuckoos are very Resolute 51 1973 Occurrences at the first nest, a mile or so north-east of the town, . were quite remarkable, and as they have only been very briefly recorded hitherto they merit attention. Mr. Ron Bishop and his wife Yvonne, their daughter Alison, and Mr. Edwin Rich were combing a tract of open forest, in late after­ noon of a day in October, when they saw a Black-eared Cuckoo fluttering over ground and being attacked by a pair of Speckled Warblers. The intruder was so intent on its mission that it was not deterred by either its assailants or the onlookers. Nor did it give any heed to the party's poodle, which was wandering nearby. Instead, it pressed on towards a grass tussock where, presently, Mrs. Bishop saw a nest. Finding this to contain three eggs of the Speckled Warbler, the four spectators at the bush drama retired a short distance and watched intently. They saw the cuckoo return at once and force its way past the attacking warblers until it entered the nest. Then, surprisingly, one of the warblers also forced its way into the nest. Within seven or eight seconds both birds emerged and the cuckoo flew off, still pursued by the warblers. All of these movements were made, as far as the watchers could determine, in vocal silence on the part of the cuckoo and only agitated twitters by the warblers. Re-examination of the nest disclosed three eggs again, but this time one was the cuckoo's product. Moreover, one of the warbler's eggs was broken, apparently through the struggling of two birds within the confined space of the chamber. It was presumed that the cuckoo carried off the third warbler's egg in its beak (or throat?), but the bird's exit was so hurried that this could not be determined. What astonished the observers most of all, in that eventful short period, was the resolution of the cuckoo. This, it seemed, verged on fanaticism. "The bird's actions," one of them said, "were almost awe­ inspiring. Not only was it attacked by the warblers, but it could see four persons and a dog close by, and yet it continued pushing forward to the nest. The urge to lay its egg must have been very strong." Something should be said, too, regarding the resolution of the Speckled Warblers. This species, unlike most other ground-nesters, does not appear to practise injury-feigning, but (as previously men­ tioned in the Australian Bird Watcher, 3 : 43-4, Dec. 1967) when carrying food to a nest it is much given to "freezing", for quite long periods, if it sees an intruder nearby; and the nestlings sometimes join in the defensive tactics by emitting a curious hissing sound when disturbed. Surely, then, admiration is merited by a small bird which, in addition to using such safeguards, will fight actively in defence of its nest, as manifested in the drama described above. Yet, after all, the struggles of both the cuckoo and warblers went to waste; for, next day, the nest was found to be in disorder and empty and its owners could not be seen. 52 ' CHISHOLM, Cuckoos are very Resolute [ Bird Watcher It may be, however, that the warblers remained thereabouts, since more recently another nest of the species was found in the same area.