December ] BERULDSON: Eggs of Brush Cuckoo 281 1978 The Eggs of the Brush Cuckoo - Cacomantis variolosus INTRODUCTION It has long been recognised and is well documented that several species of cuckoo occurring elsewhere in the world have developed an ability, not only to produce an egg similar in appearance and size to that of each of the principal host species, but to vary that similarity from one area to another as the principal host changes. No such habit has been recorded for Australian cuckoos. I suggest that the Brush Cuckoo Cacomantis variolosus, has developed such a habit at least within Australia. HISTORY Some of the early egg collectors were puzzled by an unusual type of egg sometimes found in the nests of several species of small birds in north-eastern Queensland. It is known that other specimens of this unusual egg were collected in clutches of eggs of the Brown-backed Honeyeater Ramsayornis modestus, but not distinguished from those of the honeyeater. Some of the eggs still remain unsorted in both museum and private collections. Several early collectors, who did recognise these eggs from the host species' eggs, thought they may have belonged to the Chest­ nut-breasted Cuckoo Cacomantis castaneiventris. To this day some of these eggs are still so labelled. Little interest appears to have been taken in this problem over the past half century or more. More recently a subtle variation in the eggs of the Brush Cuckoo in New South Wales has been suspected. None of the early egg collectors appear to have suspected or detected this variation. DISCUSSION Variation A (suspected): Egg, difficult to distinguish from the eggs of the Brown-backed Honeyeater. White, oval-shaped, smooth lustrous surface, very sparingly marked with small spots and blotches of blackish-brown. It tends to differ from the eggs of the honeyeater by usually being a more true oval shape and by having a very faint bluish tinge in the ground colour (only dis­ tinguishable by placing the eggs of both species side by side under a strong white light) and by being slightly more lustrous. I had seen a number of these eggs in collections, some labelled "Chest­ nut-breasted Cuckoo", and, like some early collectors, puzzled over them. I now feel quite sure that these eggs were laid by the Brush Cuckoo. They have been found only in north-eastern Queensland between approximately 20o South latitude and Cape York, and mostly between Ayr and Cairns. Very few of the well known eggs of this Cuckoo have ever been collected from that area, yet the species is not regarded as uncommon there and is present thoughout the normal breeding season, September/ October to January/ February. Most of the eggs are with clutches of eggs 282 BERULDSON [ Bird Watcher of the Brown-backed Honeyeater, but have been found in occupied nests of the following species, especially in recent years: White-breasted Honeyeater- Ramsayornis fasciatus Rufous-throated Warbler - Canopophila rufogularis Large-billed Warbler- Gerygone magnirostris Brown Honeyeater - Lichmera indistincta Northern Fantail- Rhipidura rufiventris Leaden Flycatcher- Myiagra rubecula Red-backed Wren- Malurus melanocephalus Lovely Wren - Malurus anabilis Lemon-breasted Flycatcher- Microeca flavigaster Variation B (suspected): Similar to the well known and docu­ mented egg of the Brush Cuckoo but is consistently of pale cream background colour (as distinct from the usual creamy-white, greyish or bluish-white of the common egg) and noticeably smal­ ler. The markings also tend to be paler brown. This type of egg is usually found with the following host species, the eggs of the first two of which it very closely resembles, in appearance and size: Rufous Fantail - Rhipidura rufifrons Grey Fantail - Rhipidura fuliginosa Willie Wagtail- Rhipidura leucophrys The well known egg of the Brush Cuckoo is usually found in the nest of the following species, whose eggs the Cuckoo's egg resembles, especially the first two: Leaden Flycatcher- Myiagra rubecula Satin Flycatcher - Myiagra cyanoleuca Restless Flycatcher- Myiagra inquieta Brown Flycatcher- Microeca leucophaea Rose Robin - Petroica rosea Scarlet Robin - Petroica multicolor Red-capped Robin - Petroica goodenovii CONCLUSION To date no conclusive evidence exists to demonstrate the sug­ gestions made here. The ideas are offered to generate interest in the hope that someone with sufficient time will: a) carry out the necessary exhaustive field study in north-eastern Queensland and b) carry out the necessary examination of all egg collections, to produce the facts necessary to arrive at satisfactory conclusions. There is now also the question of what type of egg is laid in north-western Australia. By G. R . Beruldson, 18 Caber St. , Kenmore, Queensland 4069. .