Reproductive Activity of Force-Paired Cockatiels (Nymphicus hollandicus)

-In some monogamous birds random force-pairing of mates results in successful reproduction. In addition, prior social experience with a mate may enhance subsequent reproductive success. We investigated the influence of force-pairing and prior pair association on reproductive activity in Cockatiels stimulated to breed by long daylengths and nest-box access. Birds force-paired at the onset of long days had reduced reproductive activity compared to birds force-paired prior to long days. Both groups of force-paired birds displayed less activity than established control pairs. Birds force-paired prior to long days but then reunited with former mates at the onset of long days did not show impaired reproductive activity compared with controls. We show that force-pairing can lead to some breeding activity in this species and that mate familiarity improves the reproductive activity resulting from forcepairing. Furthermore, pairs with histories of breeding do not require continuous mate access to maintain pair bonds. Received 1 February 1988, accepted 23 August 1988. COCKATIELS (Nymphicus hollandicus) are small (ca. 100 g), granivorous, sexually dimorphic cavity-nesting parrots that inhabit arid areas throughout much of Australia (Cayley 1938, Blakers et al. 1984). They are colonial and monogamous; as in other Cacatuini species, both sexes incubate and care for the young (Brereton 1963). It is generally accepted that pair bonds in the wild are quite stable and may be lifelong, although this is not well documented (Smith 1978). In the wild, Cockatiels are nomadic, opportunistic breeders although migratory movements occur in the south of Australia (Forshaw and Cooper 1981). In captivity, photostimulation (sexual stimulation via exposure to long daylengths) dramatically enhances the amount of sexual activity elicited by nest-box presentation (Millam et al. 1988, Myers et al. 1989). Particularly in species with biparental care, mate selection for parental and other qualities is a strategy by which reproductive success may be increased (Trivers 1972, Burley 1981). The degree of selectivity of an individual should be proportional to the amount of parental investment it contributes relative to its mate (Trivers 1972). Hence, mechanisms for assuring selection of high-quality mates would be expected in individuals with considerable parental investment. Free mate choice is important for successful breeding in species such as domestic pigeons (Columbia livia; Klint and Enquist 1981) and Canvasback Ducks (Aythya valisineria). Forcepairing in the latter species (i.e. placing males and females together in pairs such that there is no opportunity for free mate choice) may result in extreme female aggression toward the male (Bluhm and Phillips 1981, Bluhm 1985). In other monogamous species, however, force-pairing is used quite successfully to induce breeding, e.g. California Quail (Lophortyx californicus; Leopold 1977) and Ringed Turtle-Dove (Streptopelia risoria; Lehrman and Wortis 1967). Mate familiarity, established through social contact or pair formation, may also influence reproductive success in some monogamous species. Among male Zebra Finches (Poephila guttata; Caryl 1976) and Ringed Turtle-Doves (Erickson 1973), exposure to familiar potential mates rather than novel partners increased the likelihood of the performance of nest-soliciting behaviors (as opposed to initial courtship behaviors). Erickson and Morris (1972) proposed that mate familiarity may decrease aggression between mates and increase male sexual behavior towards the female, thereby stimulating female ovarian development. In addition they suggested that mate familiarity may enhance reproductive success by improving pair coordination in some breeding activities, such as incubation. It is unknown whether mate familiarity enhances the performance of reproductive activities in new Cockatiel pairs or whether reproductive activity is independent of prior mate exposure and dependent exclusively on sexual stimulation elicited by environmental factors. 86 The Auk 106: 86-93. January 1989 This content downloaded from 157.55.39.253 on Wed, 08 Jun 2016 06:43:46 UTC All use subject to http://about.jstor.org/terms January 1989] Force-pairing in Cockatiels 87 The reproductive advantages of mate familiarity may explain, in part, the long-term stability of the pair bond in many monogamous species. In captive Zebra Finches, although repairing (with a new mate) occurs readily after separation from the original mate, this second pair attachment does not destroy the original pair bond (Silcox and Evans 1982). In addition, auditory contact alone can maintain established pair bonds in Zebra Finches (Silcox and Evans 1982) and possibly in Ringed Turtle-Doves (Morris and Erickson 1971), even when pair members are given access to new potential mates. Evidence of a strong tendency for pairs to reunite (after nonbreeding season separation) has also been found among Black-legged Kittiwakes (Rissa tridactyla) and Red-billed Gulls (Larus novaehollandiae scopulinus), Common Oystercatchers (Haematopus ostralegus), Great Tits (Parus major), Northern Fulmars (Fulmaris glacialis), and Buller's Albatross (Diomedea bulleri) (Richdale and Warham 1973, Mills 1973, Dunnet and Ollason 1978, Coulson and Thomas 1983, Perrins and McCleery 1985, Harris et al. 1987). In these species, mate retention (from previous breeding seasons) is associated with greater reproductive success than mate replacement. We compared the degree of reproductive activity of unfamiliar force-paired Cockatiels with that of established Cockatiel pairs when all birds were given environmental conditions stimulatory to breeding (long daylengths and access to nest boxes). We also tested whether social interactions that increase familiarity between birds force-paired during nonbreeding conditions facilitate reproductive activity when birds were subsequently exposed to stimulatory breeding conditions. Finally, we assessed the reproductive activity of established mates that were separated, exposed to novel partners, and then reunited under breeding conditions. Our findings suggest that previous mates and individuals with whom some social contact has been shared enhance reproductive response to breeding conditions in Cockatiels and so are likely to be preferred over novel mates in successive breeding attempts.