Diving Birds of North America, by Paul Johnsgard Papers in the Biological Sciences
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Diving Birds of North America, by Paul Johnsgard Papers in the Biological Sciences April 1987 Diving Birds of North America: 5 Comparative Pair-Forming and Copulatory Behaviors Paul A. Johnsgard University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/bioscidivingbirds Part of the Ornithology Commons Johnsgard, Paul A., "Diving Birds of North America: 5 Comparative Pair-Forming and Copulatory Behaviors" (1987). Diving Birds of North America, by Paul Johnsgard. 7. https://digitalcommons.unl.edu/bioscidivingbirds/7 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Diving Birds of North America, by Paul Johnsgard by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 5. Comparative Pair-Forming and Copulatory Behaviors All species of loons, grebes, and auks are monogamous, ening posture. The variable visibility of the species-spe- with adults forming strong pair bonds that are estab- cific throat and neck markings of loons is associated lished or reestablished each year, probably during the with differential amounts of bill tilting, neck stretch- spring prenesting period. The extent of remating by ing, and sometimes also head turning; in general the de- birds mated the previous year in these groups is still gree of exposure of these throat and neck patches seems largely undocumented, though at least in alcids it is to be directly related to the degree of hostility or sexual fairly high, given the relatively long life-spans and the intensity of the display. The conspicuous back pattern- tendencies of the birds to return year after year to essen- ing of loons is not obviously utilized during display, and tially the same territory and sometimes to the same it seems likely that their white underparts are related to nest site. Such conditions would promote reestablish- countershading requirements rather than being impor- ment of contracts between previously paired birds, tant as social display features. since it is not believed that in these birds pair or family Copulatory behavior has been described for all four units normally remain intact through the winter. Al- species of loons, and the general pattern seems to be though in some grebes such as the horned grebe breed- highly stereotyped and very similar in all (fig. 24). Thus, ing site tenacity and mate fidelity may be very strong unless visual aspects of species-specific plumages are (Fjeldsi 1973~))in others such as the colonial-nesting significant, copulatory behavior in loons is unlikely to eared grebe there is no evidence of this and mate serve as an effective reproductive isolating mechanism. fidelity is poorly developed (Fjeldsi 1982a). McIntyre's (1975)observations on the common loon are Pairing behavior in the loons is certainly understood probably representative of loons in general and involve a the least well of all these three groups, and as such is large sample of twelve observed copulations. She found very difficult to summarize. It is apparent (table 22) that that either sex might initiate copulation, which always all loons are highly vocal and that vocalizations are ex- occurred on land but not on a specific "copulation plat- tremely important social signals, especially in ter- form" as has at times been alleged. If the male precedes ritorial advertisement. It is also evident that much of the female to land he typically utters a "soft" call while the described "courtship" behavior of loons is little waiting for her to approach the copulation site, which more than variably ritualized hostile behavior, since it often later becomes the nest site. The female's receptive is often extremely difficult to distinguish between hos- posture is one of lowered head and bill (fig. zqA,D), and tile territorial encounters and actual pair-forming dis- when the male mounts he stands on the female's back plays between potential mates. Indeed the most or scapular area with his head directly over hers (fig. complex and spectacular displays of loons, like those of zqB,E). After treading the male walks over whichever some grebes, seem little more than highly ritualized ag- one of the female's shoulders is nearer to water (fig. gressive behavior that probably serves to avoid serious 24C). No specific postcopulatory displays occur in fighting and promote social bonding between these sex- loons, though preening and bathing behavior often are ually monomorphic species. It is thus not surprising performed by both sexes. Some nest-building behavior that, as in some grebes, "racing" ceremonies are often may also follow copulation. present, as are erect "penguin" postures that involve Pair-forming behavior in grebes, by contrast with treading water while maintaining an essentially threat- that of loons, is extremely conspicuous and highly ster- Table 22: Social Behavior Patterns and Calls of Loons 1969, I 97 I, I 982) have contributed greatly to our under- standing of grebes and their displays. Simmons has di- Red- Ycllow- vided crested grebe courtship into two categories, water Behavior throated Arctic Common billed courtship and platform behavior. The first of these is not confined to pair formation but occurs both during Calls and after pairing, though it is largely limited to the pre- Croaking X egg stage of the reproductive cycle. Platform behavior Wailing X X X includes soliciting, copulation, and sometimes cere- Moaning X X X monial nest building. Such platform behavior may pre- Long call/yodeling X X cede nesting by several months. It probably serves both Tremolo calling X X in establishing pair bonds and later also as a mechanism Short call X for fertilization of the female, and as such it may appro- priately be called "platform courtship." Postunng Solitary grebes of at least nearly all Podiceps species Antagonistic (appeasementlalarm) as well as the western grebe and the white-tufted grebe Neck stretchinglalert X X X X exhibit advertising behavior. This calling, performed by Alarmlprone X X X X solitary birds of either sex, occurs in unpaired birds Antagon~stic(threatlattack) seeking a mate, in paired birds visually separated from Hunchedlforward X X X X their mates, and in parents that have lost contact with Bill dipping X X X X their chicks. The advertising calls are typically species Splash diving X X X X specific but may also have sufficient individual vari- ability to permit individual recognition. Mutual calling, Fenc~nglpengu~nlbowjump X X X X or "duetting," has also been recorded in all six of the Surface rushing X X X X Mutual or group displays Plesiosaur raceisurfing X Snake ceremony X Circle dancelp~voting X X X NOTE: See species accounts for descriptions and possible functions. eotyped and exhibits a high degree of species specificity (table 23). Why such differences exist between loons and grebes is not at all clear, since in general there seem to be no differences in relative need for reproductive iso- lation among sympatric and congeneric forms in the two groups. As with the loons, most of the species-spe- cific nuptial plumage characteristics of grebes are con- centrated in the head and neck region, and furthermore in both groups the displays and calls are performed mu- tually and apparently identically between the sexes. In- deed, one might wonder how sexual recognition is attained in these groups; possibly it is achieved by rela- tive dominance and submissive behavior. Most of the classic observations on grebe pair-form- ing and pair-maintaining behavior have been performed 24. Comparative sexual behaviors of loons: A, soliciting, B, copulation; and C, postcopulatory behavior of arctic loon (after on the great crested grebe, beginning with the studies of photos in Hohn 1982); D, soliciting and precopulatory ap- Huxley (I9 I 4) and continuing through to much more re- proach of red-throated loon (after Cramp and Simmons 1977); cent work by Simmons (1955, 1975) A variety of papers E, copulation in yellow-billed loon (after Cramp and Simmons by Fjeldsi (1973c, 1975, 198za) and Storer (1962, 1967, 1977) Table 23: Interspecific Distribution of Some Sexual Behavior Patterns in North American Grebes Behavior Least Pied-billed Eared Red-necked Horned Western Courtship behavior Duetting X Crest erection - Head turning/shaking/waggling - Discovery ceremony (cat-ghostly penguin) - Penguin dance - Weed ceremonies -2 Triumph ceremonies X Barging or parallel swimming X Rushing ("racing") - Habit preening - Threat pointing - Platform behavior Female behavior Inviting X Rearing - Breast stroking X Male behavior Copulation call X Water treading - NOTE: X indicates presence of behavior; X? indicates uncertain ritualization; - indicates apparent absence. North American grebe species (table 23). In some spe- mony one of the birds (the searcher or "ghost diver") cies this behavior is called a "triumph ceremony," and takes the active searching role while the other waits to at least in the homed grebe it is the only mutual display be "discovered." In the crested grebe the approach by that is frequently produced by well-established pairs the "searching" bird resembles the threatening approach (Fjeldsi 1973~).In that species it often occurs after ter- made during antagonistic encounters, while in other ritorial combat or when a pair meets after a temporary species such as the red-necked grebe, horned grebe, and separation. A triumph ceremony without calling occurs eared grebe the searching bird periodically exposes itself in the red-necked grebe. in a "bouncy" posture, with the plumage depressed and Crest erection, often in conjunction with various the breast well puffed out. When within about a meter kinds of head turning or head shaking, is common in of the waiting bird, the searching bird suddenly rises many grebes and occurs in at least five of the North vertically oui of the water in a "ghostly penguin" pos- American species.