September ] 1973

CHISHOLM, Cuckoos are very Resolute

Cuckoos Are Very Resolute By A. H. CHISHOLM, Sydney

49

Among many problems associated with parasitic birds in Aus­tralia, some of the most provocative are presented by the Black­eared 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 Field­wren, 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 White­browed 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 wi th 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 Black­eared 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 change­ling 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 White­browed 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 ] 1973

Cuckoos are very Resolute 51

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 after­noon 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 awe­inspiring. 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 men­tioned 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. In this case the chamber contained a young Fan-tailed Cuckoo, and naturally- because this species is relatively large (length about 10 inches), and because the nest-entrance was not much disturbed - the conviction arose that the egg had been deposited by the beak.

As with the Black-ear, the Fan-tailed Cuckoo is strongly addicted to the use of domed nests of small birds (only rarely does it use an open structure), and in all such instances, which relate chiefly to thornbills, fairy wrens, scrub-wrens etc., it would not be possible for such a bird to enter the chamber. A similar point obtains in respect of the Pallid Cuckoo, though this species mainly adopts open nests. Between them these two cuckoos, and the common bronze cuckoos as well, have patronised a remarkable number of nests of various shapes and sizes.*

In any event, there are numerous records to indicate that some species of cuckoos sit in nests to lay their eggs and that others do the depositing, though perhaps not invariably, with their beaks. Moreover, in almost all cases the beak is used to regulate the clutch by carrying off one of the fosterer's eggs.

It would be interesting to know which method was adopted by a Narrow-billed Bronze Cuckoo which, at Maryborough in Sep­tember 1972, placed its pinkish egg in each of two nests of the Red­capped Robin and one of the Blue Wren: this in the restricted tract of forest where the Speckled Warblers had previously been imposed upon by a Black-eared and a Fan-tailed Cuckoo. Presumably a single Bronze Cuckoo was responsible for the three eggs, for the nests were within about 50 yards of each other.

The domed nest of the wren, placed in debris on the ground, may have been entered, but the open nests of the robins, sited some 10 feet up in forks of saplings, seemed too small to accommodate a cuckoo.

Anyway, that intruder had rather overdone imposition in a limited area, and so when one of its eggs hatched (thereby destroying two young robins) I removed the parasitic eggs from the other nests in order to give two very engaging little birds "a fair go".

All the occurrences here related are, of course, merely fragments touching the general story of birds that "board-out" their offspring. It is a fascinating subiect and one that has interested me ever since, as a boy in the Maryborough bushland, I stared wonderingly at a relatively large pink egg in a Wagtail's nest, and when, some time later, I found two smaller pink eggs alongside two normal green eggs in the nest of a Yellow Robin.

Inevitably, this matter of brood parasitism (as practised by cer­tain other birds besides cuckoos) has been the subject of much discussion during many years. Numbers of books devoted to it, *Footnote: For detailed lists of Australian Cuckoos and their fosterers see H. L. White (Emu, Jan. 1915, pp. 144-54) and J. N. McGilp (South Austra­lian Ornithologist, March 1956, pp. 9-12).

The young dark coloured Cuckoo ejected the young Warbler and fell out with it. Plates 12 and 13 Photos by A . H. Chisholn

Young Black-eared Cuckoo " bulging" in nest of Speckled Warbler.

54 ' CHISHOLM, Cuckoos are very Resolute [ Bird Watcher

based on various countries, have been published, and doubtless one will some day treat in detail the 13 parasitic cuckoos of Australia.

A good deal of relevant material is contained in various Aus­tralian books and journals of natural history, and there are many revealing notes buried in the nature columns of Australian news­papers. Much material of the kind is resting in my own files and diaries and can be made available to any worker willing and able to cope with a detailed discussion of the subject.

Perhaps it will be useful to add that my own writings in point include the following: "The world's strangest parents" (Nature Fantasy in Australia, London, 1932), "The cuckoo problem in Australia" (Auk, USA, Oct. 1933), " Cuckoo facts and fancies" (Viet. Nat., June 1934), "Infants that commit murder" (Bird Won­ders of Australia, Sydney, 1934 and later), "Baby farmer and weather prophet" (Channelbill; Wild Life, Nov. 1950) , "Cuckoo mysteries that remain unsolved" (Age, Melbourne, 25 j7 /'59), "The strange ways of parasitic birds" (Vict.Nat. , Jan. 1962), "Our cuckoo from Asia" (Australian Bird Watcher, June 1966).

As in other lands, each Australian bird that practises brood parasitism has characteristics peculiar to its species. But all of them have at least one trait in common, and that is strong resolution, which is exercised not only in spying upon potential fosterers but in depositing an egg in a selected nest. And, as we have seen, although the Black-eared Cuckoo is regarded as a shy species, it possesses this determination in full measure.

Nesting Whiskered Terns kill young Grebes. In January 1972, most western district swamps were full of water after the excessive rains of the previous season. They were, in most cases, teeming with nesting birds, and near Port Fairy one such swamp had nesting Coots, Fulica atra, Little Grebe, Podiceps novaehollandiae, Hoary­headed Grebe, P. poliocephalus, Marsh Crake, Porzana pusilla, and Whiskered Tern, Chlidonias hybrida.

A party of bird banders, including myself, were most interested in banding the young terns, following the success in a past season by Trevor Pescott, of Geelong, who had a recovery of a banded bird from New Guinea.

We were all surprised at the large size of the food the terns killed ; green frogs, some 4 inches long, being found in the nests, partly eaten. We had also noted several baby grebes dead near the tern nests. As I was banding one tern chick an adult bird alighted near the nest with a grebe chick. The dead bird was 5 inches long and about It inches wide, and was bleeding from a hole in the head. I can vouch for the force of such a strike as I received a sore head from a peck through my hat by one of the nesting terns.

Miss Gracie Bowker, Port Fairy, Victoria, 30 I 3 I 1972