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Home , Aechmophorus, Anatidae, Diving bird, Fowl, Great crested grebe, Grebe

THE BEHAVIOR OF THE HORNED IN SPRING

ROBERT W. STORER Museum of Zoology University of Michigan AM Arbor, Michigan 48104

The Homed Grebe ( uuritus) is a Great Grebe. The sympatry, particularly in widespread and common breeding in the Northern Hemisphere, has presumably re- the rolling pothole country of western North sulted in the of specific differences America and suitable parts of northern Europe in the nuptial and courtship patterns and , yet almost nothing has been written which are effective in preventing hybridiza- about its behavior. The purposes of this paper tion and also differences in size, gregarious- are to describe the behavior of this on ness, and feeding habits which may have re- the breeding grounds prior to -laying, to sulted in reduced competition. compare the behavior of this species with that The behavior of the of related , to offer suggestions con- is well known through the pioneering paper cerning the evolutio,n of some of the behavior of Huxley ( 1914 ) and Simmons ’ monograph patterns, and to compare behavioral with ( 1955). Papers by Wobus ( 1964) on the Red- other kinds of evidence relating to the phy- necked Grebe, by Mrs. McAllister (1958) on logeny of these . the Eared Grebe, by Nero (1959 and in Pal- The closest relatives of the Ho,rned Grebe mer 1962) on the , and by me are the Red-necked Grebe (Podiceps grise- (1963b) on the Great Grebe provide some gena), Great Crested Grebe (P. cristutus), basis for comparison, although none ap- Eared Grebe (P. nigricollis), Silver Grebe (P. proaches Simmons ’ study in completeness. occipit&) , and Taczanowskis’ Grebe ( P. Having had some field experience with all taczanowskii). The head patterns of these eight of the species concerned, I am fortunate species are shown in figure 1. Two other spe- in being able to make firsthand comparisons cies, the Great Grebe (“Podiceps” ma@r) and and to interpret the published work on these the Western Grebe ( occiden- species. ta1i.s) are somewhat more distantly related to Although my interest in the Homed Grebe the Horned’ Grebe (Storer 1967) but are in- dates from the 1936s when I first watched cluded in the discussion. transients displaying in New Jersey, most of The Red-necked and Eared Grebes, like the the observations on which this paper is based Homed, have a Holarctic distribution, but the were made at potholes above the QuAppelle’ Eared also has isolated populations in Valley of Saskatchewan in May and June 1959 and, formerly, in the Andes of Colombia. The and from 10 to 27 May 1966, and in the Minne- Great Crested Grebe is widely distributed in dosa pothole country of Manitoba from 4 to , Africa, Australia, and New Zealand. 16 May 1967. These data were supplemented The Silver Grebe is found in much of tem- by observations made in several other perate , ranging north in the since 1953 in North Dakota and Alberta and Andes to Ecuador; and Taczanowskis’ Grebe, by notes on wintering birds in California and a close relative of the Silver Grebe, is confined transients in Michigan. to Junin at 13,400 ft elevation in Peru. Most of the observations were made from The Great Grebe is widely distributed in South a parked car, which proved a satisfactory America from southern Brazil and Peru to blind and was sufficiently large for operat- Tierra de1 Fuego, but unlike the Silver Grebe, ing both a motion picture camera and sound it is not found at high elevations. The Western equipment. Motion pictures have proved par- Grebe is found in western , ticularly valuable in describing complex be- ranging south to the Mexican Plateau. Thus havior and in preparing the figures. the Homed, Red-necked, and Eared Grebes For ease in analysis, the complex courtship are sympatric in varying combinations with ceremonies are broken down into simple pos- the Great Crested Grebe in Eurasia and with tures, movements, vocalizations, and displays. the Western Grebe in North America. In The terms “posture” and “movement” are used South America, both the Silver and Taczanow- for the simpler elements of more complex pat- skis’ Grebes occur on Lake Junin, and the . “Display” and “ceremony” are used in Silver Grebe is widely sympatric with the the sense of Simmons (1955:182), who adapted

The Condor, 71:180-205, 1969 D801 BEHAVIOR OF THE IN SPRING 181

FIGURE 1. Heads of the six_ species of Podiceps, sen.s-us&i&o, in nuptial __plumage. A.__ P. tacmnowskii,_ B. P. cristatus, (2. P. occipital& D. P. au&us, E. P. grisegenu, F. P. nigricolh. Vertical hatching, rufous (coarse) or red (fine); horizontal hatching, gray; stippling, yellow or buff.

Huxleys’ usage (1914). The names used for of a lone bird, members of a pair can usually the comfort movements are taken from Mc- be distinguished when they are together. Kinney (1965) because these movements in The head plumes are conspicuous in dis- grebes are in general homologous with those plays and the positions of these plumes are in waterfowl and probably many other birds. integral parts of the displays. In the Cere- The other names for behavior patterns are monial Turning Away and the posture pre- largely taken from the works of Simmons and ceding the Weed Trick, all the plumes are Huxley. In a few cases I have coined new flattened against the head. The Furtive pos- names, hopefully using words which aptly ture is similar, except that the -tail is describe the behavior without implying pur- raised; the raising of the duck-tail may thus pose. be an expression of appeasement or anxiety. Of all kinds of behavior, courtship differs In Advertising, the tippets and horns are fully most from one species to another. I have spread vertically but little flared out, whereas therefore concentrated on studying and de- in Rearing and before, during, and dismo8unt- scribing this aspect. But because elements of ing after , the tippets are fully courtship patterns were prosbably derived from spread and flared out so that they are almost day-to-day behavior, discussion of the latter at right angles with the sides of the head. is needed background for any discussion of At the height of the Dance and in the origins of courtship displays. the Weed Rush, the horns and tippets are held in a posture intermediate between those dur- THE NUPTIAL PLUMES AND DISPLAY ing Advertising and copulation. From this it seems likely that flaring of the horns and tip- In nuptial plumage Homed Grebes are strik- expresses a strong sexual component in ing birds. The neck and sides are bright displays. chestnut, and three groups of plumes adorn The function of the chestnut color of the the head: the rounded, black tippets, the buffy neck and sides is not clear. In part, it may lateral crests or “horns,” and the small, medial, be cryptic, for birds in nuptial plumage are black “duck-tail” on the crown. Males and far less conspicuous on the potholes where females are similar, but the females are they breed than birds in winter plumage smaller, their nuptial plumes are shorter than would be. It also may be part of the pattern those of the males, and the chestnut of the which functions in species recognition, for the neck and flanks often is paler and duller. Eared Grebe, the species which most resem- Thus, while it often is difficult to tell the sex bles the Homed on the breeding grounds, has 182 ROBERT W. STORER

a black neck. The position of the line of de- Pre-flight behavior and taking-off were ob- marcation between the chestnut of the neck served at the same two potholes on the eve- and the white of the breast is probably sig- nings of 15 and 16 May 1966 between 20:30 nificant. At most times, the white of the under- and 22:O0. I have also seen this behavior on parts remains below the waterline, but in the Huron , near Ann Arbor, Michigan. Advertising, when conspicuousness is advan- Three Homed Grebes were on the river shortly tageous, the head is stretched upward and after sunset on 20 April 1961. Two of the the white of the somewhat puffed-out breast birds, possibly paired, remained close together is prominent below the chestnut of the neck. on the water. About 19:27 ESTthe lone bird assumed the pre-flight posture and swam LOCOMOTION about, turning this way and that in a “nervous” Flying. On the breeding grounds, Homed fashion. Twice it dove, I thought with the Grebes fly more than one might expect. I wings slightly spread, wing-flapped, did at have observed them flying under at least four least two swimming-shakes, and once flapped sets of circumstances: approaching their mate across the water toward the pair before taking after a separation, attacking another bird, fly- off at 19:37. It did not circle but flew directly ing away from a pothole in the evening, and east over a railroad bridge, possibly landing flying upwind. Flying to the mate occurs beyond on the river. occasionally when members of a pair are sep- Upwind flights are seen on very windy days arated and one of them Advertises loudly. and serve to take the bird from the lee side Such a flight may result in a Discovery Cere- of a pothole to the windward one. I saw one mony in both the Homed and Red-necked male make such flights, once on the afternoon Grebes. In attacking another bird, a Homed of 16 May 1966 and twice within 6 min Grebe, usually a male, first uses an intense on the following afternoon. The last flight threat posture, then flies low over the water was filmed. The pre-flight posture resembled at the other bird, pattering with his feet. On that of the evening flights except that the head landing, he may engage his opponent on the was held somewhat lower and more forward, surface or, more frequently, both dive and probably because of the strong wind; and the the pursuit continues under water. bird remained facing the wind the whole time Flight occasioned by the other two sets of the attitude was used. The female of another circumstances is characteristically preceded pair made a flight of 20 to 30 ft against a by a special pre-flight posture (fig. 2). In wind which was strong enough to make white- this posture, the head is held high, about as caps on the pothole. Before landing, this bird in the Advertising posture, but the crests and hovered briefly with her feet in the water. neck are “slicked down.” The bill is Swimming and diving. Homed Grebes swim pointed somewhat above the horizontal, and on the surface with alternate strokes of the the head is held back but the neck is more feet, but when resting they usually keep one nearly vertical than in the Z-neck posture. foot shipped under the wing and maneuver Birds in the pre-flight posture swim about with the other. Under water, simultaneous “nervously” for from several seconds to a min- strokes of the two feet are the rule. The two ute or two before taking off. Before the grebes commoner types of dive, the “feeding dive” settle down to , they may visit potholes and the “springing dive,” described by Law- for a day or more and then leave. I do not rence for the Western Grebe (1950:3), are know whether these are transients on their also the common types for the Horned Grebe, way north or local birds visiting several pot- but in the latter species the two types grade holes before selecting one for nesting, or both. into each other. Shortly before submerging, The birds leave the potholes well after sun- the feathers of the head, neck, and body are set. For example, on 15 May 1959 all nine “slicked down,” expelling most of the air be- birds which spent the day on a pothole near tween them and the skin and thereby increas- Fort QuAppelle,’ Saskatchewan, left between ing the birds’ specific gravity (fig. 2). When 20:55 and 21:21 MST,the apparently unmated an Eared Grebe is on the surface, the body bird leaving first and landing on a pothole feathers, especially those near the tail, are across the road, and the others leaving in pairs erected more than those of a Homed Grebe, at 21:05, 21:16, 21:20, and 21:21. The pairs and they give the bird a characteristic high- circled the pothole gaining altitude before fly- stemed look. The slicking-down movement ing off, and none landed on the across before diving has thus become exaggerated the road, although the lone bird which had and probably has assumed a signal function landed there earlier Advertised loudly while as well as that of reducing the birds’ specific the last two pairs were circling. gravity. BEHAVIOR OF THE HORNED GREBE IN SPRING 183

G

I J

-.

H

FIGURE 2. Day-to-day behavior of the Horned Grebe. A, B, and C. stages of the swimming-shake D. bathing, E and F. wing-and-leg-stretch, G. both-wings-stretch, H. looking under water, I. wing-flapping J. pre-fhght posture, K. resting posture (“pork-pie”), L and M. head-bobbing, N. threat, 0. appeasing posture P. Triumph Ceremony, Q. Eared Grebe in normal posture before slicking down, R. Homed Grebe in same posture, and S. slicked down. 184 ROBERT W. STORER

I have no detailed notes on “alarm dives” was about to catch it, both swam under the or “surface dives” (Lawrence 1950:4), but wharf. A few second later, the grebe swam they may also be used by Horned Grebes. out with the , worked it around in its , These birds may attack members of their own and swallowed it head first. or other species by threatening and diving or At all seasons, most of the food is obtained by flying and diving. In the latter case at by diving. As in the above instance, large prey least, the wings may be used in submerging. such as fish or is brought to the I have not seen Homed Grebes use Ripple surface and pinched and shaken before it is Dives like those used by Great Crested Grebes eaten. Small items are evidently swallowed in the Discovery Ceremony (Huxley 1914: under water, for I have not seen foraging 512; Simmons 1955:190) or by Pied-billed grebes surface with small in the beak Grebes ( podiceps). The other or make swallowing motions when I did not’ ritualized dives employed in courtship are dis- see food in the beak. Wetmore ( 1924:13) cussed elsewhere. mentions Homed Grebes feeding on insects Resting. Homed Grebes, like other mem- cast on the surface of the water, and I have bers of the , rest in the well-known several times watched these birds picking up “pork-pie” attitude with the head directed insects from the surface or from emergent forward and lying to one side of the neck vegetation, especially when there was a large (fig. 2). While in this posture, one foot is hatch of midges. Like Great Crested Grebes often shipped under the wing. When one foot (Simmons 1955:98), Homed Grebes occa- is so shipped, the opposite side of the body sionally look for food by dipping the head so rests somewhat lower in the water. In seven that the eyes are below the surface (fig. 2)) of eight observations, the grebes were seen to but on potholes where small invertebrates are keep the head to the right (or high) side of abundant, the birds evidently find their food the neck when the right foot was shipped, while they move about under the water. and vice versa. According to Simmons (in Periods of foraging usually alternate with litt. ), Great Crested Grebes also ’ rest with the periods of , and for the several days head on the high side. prior to incubation, periods of nest-building and sexual behavior are interspersed with FORAGING AND -EATING these. Observations on a pair of Horned Studies by Wetmore (1924) and Munro (1941) Grebes near Fort QuAppelle’ indicate that have shown that Horned Grebes take a con- in the period prior to egg-laying the female siderable variety of food. spends more time foraging than the male. and fish predominate in stomachs of’ birds The female of this pair laid the first two taken on salt water during the winter, and of her clutch between 16:37, 17 May, and aquatic insects make up the bulk of the food 14: 13,19 May 1966. On 14 May between 10:00 taken on the breeding grounds. The methods and 15:32, she spent approximately I72 min of foraging are also diverse. On 26 October foraging; the male spent 86 min. Between 1953 I watched a Horned Grebe diving in 8:50 and 11:30 the following day, she spent shallow water near a pier at Monterey, Cali- 112 min foraging and the male 80; and be- fornia. While on the surface, the grebe moved tween 12:27 and 16:27 on 16 May she foraged its feet alternately, but while under water 112 min, the male 95. This greater amount of used them simultaneously, and even when foraging is probably correlated with the pro- pursuing a fish it kept both wings folded duction of eggs. against the body. The bird chased several Since describing pellet-casting in the Horned schools of small fish (approximately three Grebe ( 1961), I have observed the process inches long). The schools successfully evaded at least three times and collected two of the the bird by circling sharply to the left or to birds at known times after they cast pellets. the right or by dividing into two groups, one I was not able to retrieve the pellets. On 26 circling in each direction and both coming May 1966 D. E. Gill and I watched the pair together after the bird passed between them. mentioned above. The male, after being re- These chases were repeated several times, the bird making two or three attempts in one lieved at the nest, preened for 5 min or so dive. Finally, after making an unsuccessful and began a series of approximately 15 drink- pass at a school, the bird found a fish which ing motions. Then leaning his head fonvard, had become separated from the school and he shook it several times and coughed up an without surfacing, swam it down. The fish irregularly-shaped pellet about two inches swam rapidly near the surface but made no long. He dove and started foraging almost attempt to dodge or circle. Just as the grebe immediately. When I collected him 2 hr later, BEHAVIOR OF THE HORNED GREBE IN SPRING 185 there was a mass of remains and one pyloric lobe even during the casting process. or two feathers in the large chamber of the On the other hand, when grebes are feeding stomach and a plug of feathers wedged tightly on fish, feathers may function to hold the in the pyloric lobe. On 6 May 1967 J. A. bones in the center of the stomach and in Feduccia and I watched pellet-casting by this way may protect the walls while the bones another male Horned Grebe. This was pre- are being dissolved by stomach acid. The fact ceded by at least 10 drinking motions and that the bones are dissolved makes frequent followed by the birds looking under the water pellet-casting unnecessary and permits the ac- as though for the pellet. Shortly afterwards cumulation of feathers in the stomach. he started feeding and was collected 23 min later. The large chamber of his stomach con- COMFORT MOVEMENTS tained 9 leeches, at least 197 caddis-fly larvae, In birds, comfort movements tend to be con- 1 water boatman (Corixidae ), 7 beetles (2 servative, and homologous movements are Dytiscidae, 5 Gyrinidae), 3 fruit flies (Dro- often easily recognizable in birds of widely sophilidae), 6 large or medium-sized feathers, separate orders. Hence for these movements, and 17 very small feathers or parts of feathers. I think it best to use a nomenclature which The pyloric lobe contained a plug of 260 hair- may be applied to all or most birds. To date, like feather fragments. Assuming that no food McKinneys’ analysis of the comfort movements items remained in the stomach after the pellet in waterfowl (1965) appears to be the closest was cast, the bird caught and ate food items approach to this ideal, and I have followed at the rate of 9.4 per min. Where food is this it where possible. Because the tail of grebes abundant and easily taken, the time spent for- is minute, motions associated with it are re- aging is probably a good indication of the duced, lost, or overlooked. Thus they are not amount of food taken. mentioned in the descriptions which follow. The function of feather-eating by grebes Swimming-shakes (McKinney 1965: 132-133) has been discussed by many authors, but with are commonly observed in Horned Grebes few conclusions. Wetmore (1924:4) noted (fig. 2). The movements are essentially like that the pyloric lobe of the stomach is almost those of the . They are frequent in invariably plugged with feathers and “that bouts of preening and often terminate such feathers occur in greatest abundance and most bouts. They occasionally appear, I think, as commonly in stomachs containing remains of displacement activities (in the sense of’ Tin- and hard-bodied insects, and that they bergen 1951: 113), as when members of a pair are less abundant (or are even occasionally meet and pass each other while foraging, be- absent) in gizzards containing soft-bodied fore mounting, or before taking flight. I have larvae or crustaceans that are easy of digestion no evidence that these swimming-shakes have and assimilation.” He went on to suggest that become ritualized or that they have a special the feathers act as a strainer to prevent fish signal function. I have not seen grebes per- bones or large pieces of chitin from entering form body-shakes, the corresponding move- the intestine. ment on land ( McKinney 1$X%:126). In examining the intestines of grebes for Rapid head-shakes, similar to, those of the parasites, I have found the contents quite free waterfowl ( McKinney op. cit.: 135), are per- from bits of chitin or other “roughage,” even formed by Homed Grebes as a comfort move- when the only feathers in the stomach were ment, often in bouts of preening and after bill- those of the pyloric plug. From this, I con- dipping. Ritualized head-shaking has become clude that the plug is an efficient strainer. a part of the Head-shaking and Discovery Furthermore, the fact that adult grebes feed ceremonies (which see). I once recorded a Horned Grebe in what feathers to their newly hatched young sug- may correspond with the wing-shake of the gests that early establishment of such a plug Anatidae (op. cit.:130-132). The feathers of may be important. The masses of feathers in the closed wings were ruffled and the wings the large chamber of the stomach are a dif- shaken simultaneously in a motion which re- ferent matter. As I have mentioned in an minded me of a swimming-shake. This may earlier account of pellet-casting (1961), grebes be the evolutionary source of Wing Quivering living on fishless bodies of water and de- (see p. 199). pending on for much of their diet A common motion in Homed Grebes may rapidly accumulate indigestible chitin in the correspond with the wing-shuffle of stomach. This requires rather frequent pellet- (op. cit.:147-149). In this, the closed wings casting, and feathers do not accumulate in remain in their usual position on the back but the stomach, although they remain in the are moved forward and back in an undulating 186 ROBERT W. STORER motion. This may be kept up for several min- the Anatidae by McKinney ( 1965: 15%158), utes, and, as in the wing-shuffle of ducks, scratching is the most obvious in the Homed occurs after bouts of preening. Grebe. As in the ducks and the Great Crested Wing-flapping in grebes (fig. 2) closely Grebe (Simmons 1955:100), scratching is di- resembles that in the Anatidae (op. cit.: 141- rect, that is, over the closed wing. I have no 142). It is a usual sequel to bathing and less certain observations of foot-pecking, although often to preening. I once observed it, possibly I once watched a grebe with one foot shipped as a displacement activity, prior to flight. under the wing raise the wing and make mo- Foot-shaking is commonly performed by tions which could have been directed at either grebes. In the Homed Grebe, the motion re- the foot or the underside of the wing. sembles that described for ducks on the water Bill-cleaning movements like those of the ( op. cit.: 147). The motion regularly precedes Anatidae may be completely replaced by bill- “shipping” the foot under the wing and has dipping in the grebes. The latter movement is been well described by Sim (1964:71) for the frequently seen and is usually followed by Red-necked Grebe. In the Homed Grebe the head-shaking movements. The two movements motion is very rapid and the foot is not held have become ritualized into the Dip-shake of up like a flag for several seconds as it fre- the Western Grebe (Nero 1959:294). I once quently is in the Western Grebe. The func- saw a Homed Grebe bill-dip and then head- tion of the motion appears to be removal of shake among a series of aggressive actions, a water from the foot. situation in which the combined movements The three stretching movements, wing-and- appeared to be a displacement activity. leg-stretch, both-wings-stretch, and jaw-stretch, Of the bathing motions described by Mc- described by McKinney ( 1965:150-152) for Kinney for the Anatidae (1965: 171-176), head- the Anatidae are all commonly performed by dipping and wing-thrashing are commonly grebes (fig. 2). In the wing-and-leg-stretch, performed by grebes (fig. 2). During bath- one foot is extended backward over the water ing, Horned Grebes puff out the breast more, and the toes spread. The wing of the same hold the head lower, and keep the body more side is then spread and held back for a second nearly upright than ducks do. Wing-flapping or two after which it is folded, and finally, and preening usually follow bathing. A grebe the foot is brought forward. This stretch is may dive several times while bathing, each often seen in bouts of preening. Both-wings- time emerging in the bathing posture. stretches are less common in the Homed Grebe Oiling and a great variety of nibbling mo- than wing-and-leg-stretches. In the former tions are common preening activities of grebes. (fig. 2), the neck is held low, on or near the I have made no attempt to analyze them and surface of the water and stretched forward, doubt that there are many interspecific dif- the bill is pointed upward at an angle, and ferences in these movements. The motion of the folded wings are raised, much as in Mc- turning the head back and running the bill Kinneys’ photograph of the in this through the remiges or scapulars has become attitude ( 1965:pl. I). In contrast to the Pied- ritualized as Habit Preening (see p. 193). billed and Western Grebes (personal observa- AGONISTIC BEHAVIOR tions ), the Red-necked Grebe ( Wobus 1964: 29), and the Great Crested Grebe (Simmons While Horned Grebes during migration may 1955:100), the raised wings are not spread, remain together in flocks with little apparent nor have I seen the stretch prolonged beyond aggressive behavior, on the breeding grounds a second or two, or given repeatedly as is they become pugnacious, defending their ter- ritories vigorously against others of their spe- frequently the case in Western Grebes. The cies and at times even putting ducks to rout. posture of the head and neck in the four The common form of threat (fig. 2) corre- species is similar. The both-wings-stretch is sponds to the Forward Display of the Great the only comfort movement of grebes in which Crested Grebe (Simmons 1955: 138-139). I have found appreciable interspecific differ- Threatening birds may make short dashes at ences, and I have no explanations to offer for rivals, swimming very rapidly and stopping the origin and significance of these differences. suddenly, or they may rush their rivals more I have seen Homed Grebes jaw-stretch both vigorously, half flying and half pattering over while on the nest and while on the water. the water. If the rival holds its ground, breast Neither it nor the other two stretching move- to breast fighting may follow. In this the ments appear to have become ritualized or wings are held open and may be used to raise incorporated into the displays of grebes. the bird above its opponent. Although it is Of the cleaning movements described for difficult to determine just how the feet are BEHAVIOR OF THE HORNED GREBE IN SPRING 187 used, it is my impression that they are used bond, as opposed to those which are directly for combat as well as for keeping the bird up- related to the act of , are here con- right. If an attacked or threatened bird dives, sidered courtship. In grebes, mating usually the attacker almost always dives and continues takes place on the nest or on a similar plat- the pursuit under water. If an attacking bird form built by the pair. Thus a strong pair catches another by the head or neck, both bond must be established before building and, may dive and come up with the attacker still in turn, mating can take place. It is therefore holding on. Drawing an analogy from water- not surprising that the courtship and mating behavior, several authors have incorrectly behavior should be quite different. The described similar behavior in Pied-billed species-specific elements of the behavior Grebes as forced copulation (see McAllister which prevent the formation of mixed species and Storer 1963). pairs are thus largely found in courtship be- Token Diving is a well-known threat dis- havior.’ The mating behavior varies much less play in the Great Crested (Simmons 1955: from species to species. 139) and Red-necked Grebes (Wobus 1964: Upright Posture. The neck is stretched up- 54). I have seen it performed by the former ward to nearly its full length, the body axis species and by both the European and Amer- remains horizontal, and the bill is most often ican races of the latter, but never by the held horizontal. Variants of this posture occur Horned Grebe or any other species. in Advertising and several other displays, in- The appeasing posture of the Horned Grebe cluding agonistic ones. The tail is frequently in general resembles the “furtive-posture” of cocked when this posture is used in courtship the Great Crested Grebe (Simmons 1955: 142). displays. In it, the Horned Grebe holds the head high The use of this term stems from Simmons ’ and the crests and tippets flattened against ( 1955:141) description and illustration of an the head and neck, but it raises the duck-tail “upright pre-attack posture.” The term “up- and holds the head back so that the posture right threat posture” is in common use in be- of the bird resembles the letter “Z” (fig. 2). havior studies of the (e.g. Tin- In territorial encounters, it is usually the bergen 19535354) and its relatives; no male who attacks intruders. After driving off homology with this behavior of is in- his opponent, the male returns to his mate and tended by the use of the term “Upright Pos- the two assume the Hunched Posture (?Cat ture” in grebes. Display) and swim side by side for a foot or Penguin Posture. The neck is stretched up- two, trilling (fig. 2). This I have called the ward and the body held nearly vertically. Triumph Ceremony in my notes, although the This posture is maintained by vigorous mo- term may not be entirely appropriate because tion of the feet under water. Thus, while it the ceremony is sometimes used when there appears to the observer as a posture and is has been no aggressive encounter. It is quite here so classified, it could also be classified unlike the “swimming-together” of Great as a movement. The Penguin Posture appears Crested Grebes described by Simmons (1955: to be related to the Upright Posture, and in 188), but it might be an evolutionary fore- some displays may grade into it. I believe runner of the use of the Cat Display by the that the degree to which the body is held ver- latter species in aggressive situations (op. cit.: tically, and hence the height of the head above 144). the water, is directly correlated with the in- That Homed Grebes defend their tensity of the display. As evidence for this vigorously has been mentioned by several authors. Of these DuBois ’ account (1919:171- view, I can point out that as Homed Grebes 173) is one of the most detailed. While ob- approach each other for a Penguin Dance or serving Homed Grebes from a parked car, I for a Weed Rush, they rise higher and higher occasionally saw them become uneasy and in the water, and as they move away from bob their heads forward and back as a each other after these displays, they gradually does, but with a slower, smoother motion (fig. settle into the swimming posture, and that the 2). Greater uneasiness, especially when the Penguin Posture is rarely assumed unless one mate was not near, more often resulted in bird is close to or touching another and rarely Advertising, and when still more alarmed, maintained for more than a few seconds un- they often swam away in the Furtive Posture. less a second bird responds by making an COURTSHIP appropriate display. The expression “Penguin The displays and ceremonies which result in position” was used by Huxley (1914:560) for the formation and strengthening of the pair this posture. 188 ROBERT W. STORER

Hunched Posture. The bird appears to ride remarks on its similarity to displays of birds high in the water because the body feathers of several unrelated groups. Not mentioned are partly erected. The head is held close to by Daanje are the very similar defensive dis- the body and the ornamental plumes are plays of several species of (e.g. Asio otus spread. This term and Spread-wing Posture and Bubo virginianus, figured in Bent 1938, were suggested to me by Simmons (in litt.) pls. 35 and 75, respectively). As in the and serve to break down the Cat Display of Hunched Attitude, the apparently increased such species as the Great Crested Grebe into size of the bird enhances the aggressive effect its components. The Hunched Posture is of a display in which the wings are spread. probably derived from agonistic behavior. It Barging. I first used this term in my field is used by Homed Grebes in situations in notes to describe slow forward motion in the which the impulse to attack appears to be Penguin Posture. The shape of the blunt slightly stronger than that to flee, and in the bodies, especially those of the smaller species, Triumph Ceremony of a pair after an aggres- in this posture suggests barges, and the slow sive encounter with another bird or birds. Its motion produced by an obviously great ex- effectiveness in agonistic situations probably penditure of effort emphasizes the similarity. results from the apparently larger size of the In low-intensity Barging when the body is not bird when the feathers are raised. raised vertically to its full height, it can often Bouncy Posture. The head is held low over be seen that the tail is cocked. Barging is a the back, the bill directed forward, and the component of the Barge-and-Dive Ceremony breast puffed out and raised. The tail is of the Silver and Taczanowskis’ Grebes (Storer, cocked and the posterior part of the body held MS ) and appears as a variation in the Weed low in the water (fig. 3). This posture Dance of some species. It also forms part of a striking resemblance to the Bridling of the a courtship ceremony of the Western Grebe, Chestnut-breasted Teal (Anus castunea) as in which species it has been called “water figured by Lorenz (1941:257, fig. 31). treading” by Nero (in Palmer 1962:lOl). The The name was suggested by the round, taut latter term, however, does not convey the idea appearance of the bird and by its sudden of forward motion and might more appro- swinging into the dive which immediately priately have been applied to the Penguin follows. The Bouncy Posture is a component Posture. of the Bouncy Dive Display, which in turn On the one hand, Barging is closely related forms part of the Discovery Ceremony od all to the Penguin Dance, as in the Weed Dances but the Great Crested Grebe. mentioned above, and on the other hand, it There seems no reason for homologizing may grade into Rushing (see below). this posture with the post-copulatory Bridling Rushing. This term is used here for rapid of ducks, which Daanje (1950:79-89) believed motion in the Penguin Posture. It is a com- to be “an intention movement indicating rapid ponent of the Weed Rush of the Homed Grebe swimming.” Once, while watching a Homed and a display of the Western Grebe (the Grebe bathing, I saw it dive two or’ three “Race” of Nero, in Palmer 1962:loO). I have times, each time coming up in the same place selected the term “Rushing” because it de- in a posture which I could not distinguish scribes the motion without implying the com- from the Bouncy Posture. Future observations petitive or esthetic motivation of such terms may show that this is a regular part of the as “racing” or “dancing.” bathing routine, and therefore the probable In the Barge-and-Dive Ceremony, Barging source of the display. and Rushing may intergrade (Storer, MS). Spread-wing Posture. The wings are par- The increase in speed as Homed Grebes ap- tially spread and the upper surface directed proach each other, rise higher into the Pen- forward so that the plane of the wings forms guin Posture, and perform the Weed Rush an angle of approximately 45” with the suggests that the speed of Rushing may be horizontal (fig. 3). This posture is used while directly correlated with the intensity of the the bird is in the Hunched Posture and greatly display. accentuates the apparent size of the bird. Porpoising. A bird in the Bouncy Posture Birds in this posture face the bird to which suddenly leaps into the air, its body arched, they are displaying. As far as I am aware, the and dives into the water (fig. 3). This is per- Spread-wing Posture is only used as a com- formed by Silver Grebes, and in a sommewhat ponent of the Cat Display (see below). less exaggerated form by Taczanowskis’ Daanje ( 1950) considers this action a ritual- Grebes, in the Discovery Ceremony. This ization of an intention movement of flight and of dive appears to be a ritualization of BEHAVIOR OF THE HORNED GREBE IN SPRING 189

FIGURE 3. Courtship behavior of the Horned Grebe (and other species). A. Advertising, B. Bouncy Pos- ture, C. Porpoising (Silver Grebe ), D. Cat Display, with Spread-wing Posture (Great Crested Grebe, after Berg 1916), E, F, G, and H. successive stages in the Discovery Ceremony from the Cat Display and the Ghostly Penguin Display (E) to the Penguin Dance (H), I. Ceremonial Turning Away.

what Lawrence in his paper on the Western its progress. Silver and Taczanowskis’ Grebes Grebe (1950:3) called the “springing dive,” sometimes use Ripple Dives in this ceremony. a kind of dive which I have seen used by Because Great Crested Grebes also use grebes of several species in rough water. shallow dives like these when not engaged in Ripple Dive. Huxley ( 1914: 512) described, courtship, Simmons ( 1959:218) has referred but did not name, this type of underwater to them as “travelling dives.” He now agrees progression as a part of the Discovery Cere- with me (in litt.) that “the actual underwater mony of the Great Crested Grebe. This dive progression in the Discovery Ceremony needs is characterized by the birds’ remaining so a name and that Ripple-dive‘ ’ is most suitable.” near the surface that a telltale ripple marks Pied-billed Grebes (Podilymbus padiceps) 190 ROBERT W. STORER

and probably other species regularly use shal- and the bringing together of a pair which has low dives in which ripples are produced. been temporarily separated. In either case a When one can see only the ripples, it is im- Discovery Ceremony may follow. In the case possible to tell if ripple dives used under dif- of mated pairs, the frequency with which the ferent circumstances are performed similarly Discovery Ceremony results decreases as the and also to tell to what extent, if any, such pair bond becomes stronger. The strongest dives have become ritualized. I would as- response to Advertising is flying to the mate sume, however, that a regular component of followed by a Discovery Ceremony and a so complex a ceremony as the Discovery Cere- Weed Rush and, in decreasing of mony would be ritualized. strength, swimming to the mate followed by An obvious function of a Ripple Dive is to a Discovery Ceremony and a Weed Rush, a make the location of the bird performing it Discovery Ceremony without a Weed Rush, clear to a bird observing it from the surface, a Head Shaking Ceremony, (?normal) preen- a function also accomplished by a Homed ing, and merely swimming slowly together. Grebes’ performing a series of Bouncy Dives, Simmons ’ note on Advertising in the Great Advertising Display. In a full Advertising Crested Grebe (1954) appears to be the first Display, a Homed Grebe assumes an Upright good description of this display in grebes and, Posture with the base of the neck or the an- I believe, the first use of this term in studies terior part of the body puffed out. This area of grebe behavior. I have used this term, al- is white, contrasting with the rufous color of though it does not convey the strong element the neck and sides. The body feathers are of anxiety present in the motivation for the partly erected and the tippets and crests display. Mrs. McAllister (1958) has figured spread but not flared laterally (fig. 3). The and described this display in the Eared Grebe, Advertising call (see p. 200) is given from and I have observed it in all five American time to time as part of this display. species of Podiceps, sense stricto. The pos- Advertising is best described as an expres- tures used by these species and the Great sion of “anxiety” or “unrest,” but there is a Crested Grebe are all very much alike, but strong sexual element in the motivation as there are differences in the degree to which Simmons (1954:55) has stated in the case of the head plumes are raised. In the Great the Great Crested Grebe. It is a common dis- Crested Grebe, “the conspicuous tippets are play from early in the courtship season at not spread appreciably and the crest is de- least until the start of incubation. It may be pressed” (Simmons 1954:54); in the Eared used still later; Great Crested Grebes (Sim- Grebe, “both crest and neck feathers are mons 1959:217) and Eared Grebes Advertise raised” (McAllister 1958:291); and in the Red- well after the young are hatched. necked Grebe, the crests and the feathers on When members of a pair have been out of the back of the neck are almost fully erected. sight of each other for several minutes, one Advertising is similar in the Great Grebe, may Advertise. A lone bird is strongly at- “Podiceps” major (Storer 1983b:283-284), and tracted to a playback of recorded Advertising the well known tree creet call of the Western calls and will swim toward the source of these Grebe appears to be comparable, although the calls, Advertising repeatedly. This response posture used by the latter species when giving is that of a bird seeking a mate and thus is the call is less stereotyped than it is in the not primarily related to territory. I have seen species of Podiceps. Advertising elicited by other stimuli: a lone There are considerable interspecific differ- bird foraging near the shore suddenly became ences in the frequency with which Advertising aware of our presence, gave two weak Ad- is performed. On the breeding grounds, I have vertising calls, then swam away. (This sug- recorded it infrequently in the Red-necked gests a possible connection between the Ad- Grebe. Judging from Simmons ’ account (1954), vertising call and an alarm note.) Another it is more commonly given by the Great Homed Grebe Advertised when a Pied-billed Crested Grebe, and I have found it more Grebe made an upwind flight across the pot- commonly used by Homed Grebes than by hole. Horned Grebes also Advertised when a Red-necks. Wobus (1964) does not describe Red-necked Grebe took flight and circled over Advertising in the Red-necked Grebe, but the them. Similar responses to other Homed second call he described ( p. 21), “waak,” may Grebes which had left a pothole and were be the Advertising call. In the Eared Grebe, circling it were noted several times. Advertising is an extremely common form of The most frequent results of Advertising behavior and is frequently used even after the appear to be the attracting of a potential mate young have hatched. In this species, the Ad- BEHAVIOR OF THE HORNED GREBE IN SPRING 191 vertising call is, to my ears, somewhat variable, TABLE 1. Time taken by the phasesof a series of and it may be that individuals come to recog- Bouncy Dives by a Horned Grehe (expressed as number of motion picture frames at 16 per second). nize their mates and neighbors by their par- ticular variation of this call. The recognition Emerging Bouncy Posture Submerging Under water of individual birds and the appeasing rather 23 7 57 than aggressive nature of this call are pre- 15 15 8 48 sumably advantageous in reducing aggressive 17 41 behavior in colonial species like this one, ; 12 ; 26 12* which nest in thick emergent vegetation where 9 8 8 approaching birds cannot be seen until they * Emerges in Ghostly Penguin display. are close at hand. This variation is a step toward the striking variation in the corre- the Mute . The S-neck posture of the sponding call of the Western Grebe (Nero, in Great Grebe may correspond with this display Palmer 1962:96; personal observations ), which ( Storer 1963b:283). almost certainly functions in individual recog- The Spread-wing Posture is such a con- nition. spicuous feature of the Cat Display of the The resemblance of the Advertising posture Great Crested and Eared Grebes that, expect- to certain agonistic postures (e.g. the Upright ing to see a similar posture in the Homed Pre-attack and Furtive Postures of the Great Grebe, I was slow to recognize its Cat Dis- Crested Grebe, Simmons 1955: 141-142) sug- play. Its relative inconspicuousness compared gests a possible derivation from agonistic be- with the homologous display of the other two havior. In general, the Upright Posture ap- species may also account for the infrequency pears to have strong sexual and appeasement with which I have recorded it in situations elements, and the spreading of the tippets other than the Discovery Ceremony. and crests, strong sexual and aggressive ele- Whether or not the Spread-wing Posture is ments. Thus the aggressive aspect of the part of the Cat Display is a conspicuous dif- spread head plumes may partially balance the ference in the Discovery Ceremonies of the appeasing nature of the posture and the call, northern species and is probably a factor in allowing the sexual elements to predominate. preventing the formation of mixed pairs. Of Cat Display. A Horned Grebe performing the two large species, both of which have this display assumes the Hunched Posture and white cheeks, and the two small species, both droops the wings slightly and then lowers the of which have black cheeks and tufts of pale wrists; the leading edges usually remain be- feathers behind the eye, the Spread-wing tween the flank feathers and the birds sides Posture is used by one and not by .the other. (fig. 3). The display is used as part of the Diving Displays. In the early stages of a Discovery Ceremony, by the female in aggres- Discovery Ceremony, one member of a pair sive situations, and by members of a pair in of Homed Grebes performs a series of “Bouncy Triumph Ceremonies after aggressive en- Dives” (short dives from which it emerges in counters. the Bouncy Posture). In making this series The homologous display, which includes the of dives, the bird does not travel in a straight Spread-wing Posture, is well known in the line, but zig-zags somewhat, changing its di- Great Crested Grebe, having been described rection with each dive. On coming up in the and figured by both Huxley (1914) and Sim- Bouncy Posture, it may face the other bird mons (1955) and beautifully shown in an or may be oriented with its side toward it. early photograph by Berg ( 1916: 133). In her Most frequently, however, it is in an inter- paper on the Eared Grebe, Mrs. McAllister mediate position. I have never seen it face ( 1958) has described this display and pointed away from the o.ther bird while in the Bouncy out its similarity to ,that of the Great Crested Posture. As the approaches the Grebe. Her figure, however, does not show bird which is in the Cat Display, the duration the wings spread as fully as had been the rule of both the dives and the time it remains on in my observations. Silver and Taczanowskis’ the surface decreases. A tabulation of the Grebes also perform Cat Displays of this type. time taken by the phases of one series of The Red-necked Grebe has a Cat Display in- Bouncy Dives is shown in table 1. termediate between the two types but more In the final dive of the series, the diver goes like that of the Homed Grebe; Wobus figures beyond the bird in the Cat Display, which it (1964:43) and calls it the Swan Attitude turns, evidently watching the progress of the (“Schwanenstellung”) because of its resem- diving bird. The diver then emerges in the blance to the common aggressive posture of Ghostly Penguin Display. A frequent varia- 192 ROBERT W. STORER

tion is for the diver to circle the bird in the informed me that the Great Crested Grebe Cat Display with a series of short Bouncy does indeed emerge with its head forward Dives before coming up in the Ghostly Pen- like the other species. guin. In one motion picture sequence of the I have found Bouncy Dives to be a regular Homed Grebe in the Ghostly Penguin Dis- feature of the Discovery Ceremonies of the play taken at 16 frames per second, 11 frames Red-necked, Homed, and Eared Grebes. In elapsed from the time the bird first broke his work on the Red-necked Grebe, Wobus water until its head snapped back and the (1964:46) mentions a short emergence, often plumes were spread, and nine more while the of only the head, in the Discovery Ceremony; displaying bird turned to face the second bird. this almost certainly refers to Bouncy Dives, Although I have no film of the Red-necked According to Huxley ( 1914:512) and Simmons Grebe in this display, it is my impression that ( 1955:196), Great Crested Grebes use Ripple these birds emerge more slowly than do either Dives in this phase of the Discovery Cere- the Horned or Eared Grebes. Huxley (1914: mony. Huxley ( 1914: 512-513) mentions that 498) describes the slowness with which a a Ripple Dive may be interrupted by the Great Crested Grebe emerges in this display. diving birds’ putting its head and neck briefly The Penguin Dance Display. In this dis- above the surface “merely to reconnoitre his play, two Homed Grebes rise up in the water position.” It would be interesting to find out face to face (fig. 3). The axis of the body is if Great Crested Grebes assume the Bouncy not quite vertical, the breast feathers are Posture in this situation. In the Silver and puffed out, and the back feathers may also Taczanowskis’ Grebes, this part of ,the Dis- be somewhat raised. The neck is stretched covery Ceremony is not fixed; either Ripple up, the bill is pointed somewhat below the Dives or Bouncy Dives may be used, and the horizontal, the horns are raised to a nearly latter may be performed with or without vertical position, and the tippets are partially Porpoising. spread. Ghostly Penguin Display. In this component In the Homed Grebe, the Penguin Dance of the Discovery Ceremony, a Homed Grebe occurs, alternating with Habit Preening, at emerges from the last of a series of Bouncy the climax of the Discovery Ceremony. In Dives facing away from the bird to which it particularly intense bouts of Head Shaking, has been displaying. As it emerges, its body the birds may rise up in a Penguin Dance. In is nearly vertical but its head and neck are this species, I have never seen the Penguin nearly parallel to the surface of the water Dance as part of a Weed Ceremony. though arched downward (fig. 3). The horns The Penguin Dance is found in essentially and tippets are appressed to the head, but similar form in the Eared, Red-necked, and otherwise .the posture of the head and neck Great Crested Grebes. The remarkable photo- resembles that assumed during Rearing. (This graph of Great Crested Grebes in this display posture also resembles that of Western Grebes by J. H. Drenth (Brit. Birds, 50:pl. 43, 1957) during the Rushing Display.) When the bird and the accompanying text by Simmons (1957) has risen to nearly its full height, the head is supplement the earlier descriptions by Huxley raised and held almost at right angles to the (1914) and Simmons (1955). In this species, now vertical neck, and the horns and tippets the breast feathers are less puffed out than are spread. While in this position, the bird those of the smaller species, the bill is held then turns slowly toward the second bird. No horizontal, and while the tippets are expanded, call is uttered during this display. the crest is lowered. In contrast to other spe- So far as is known, this display occurs only cies, this display is used only in a Weed Cere- as a component of the Discovery Ceremony. mony and never in the Discovery Ceremony. It is essentially similar in the five species in In the Eared Grebe, the Penguin Dance is which I have observed it (the Red-necked, very similar to that in the Homed, even to Homed, Eared, Silver, and Taczanowskis’ the puffing out of the breast feathers. This is Grebes). Neither Huxley (1914) nor Sim- not shown in Mrs. McAllisters’ figure (1956: mons (1955) mentioned the rising with the fig. 1) although it is quite clear from my mo- head in the forward position in their descrip- tion picture films. In this species, it is a com- tions of the Ghostly Penguin Display of the ponent of the Discovery Ceremony and may Great Crested Grebe and Mrs. McAllister occur as a separate ceremony, but as far as (1958) evidently failed to notice it in the known, never with weeds. As in the Horned, Eared Grebe. In response to my inquiry, the Penguin Dance may accompany intense Simmons made some further observations and bouts of Head Shaking. In the Red-necked BEHAVIOR OF THE HORNED GREBE IN SPRING 193

Grebe, the Penguin Dance is in general similar ing Head Shaking in the Eared Grebe Mrs. to ,that of the Horned, but it is used in a Weed McAllister (1958:29%294) stated that the Ceremony as well as in the Discovery Cere- “tempo was military, precise but not hurried” mony. in the Head Shaking Ceremony, but fast dur- The evolution of the Penguin Dance ap- ing the Penguin Dance. Wobus ( 1964:3940) pears to be closely connected with that of distinguishes between rapid (“Kopfschutteln”) Rushing and will be discussed under that dis- and slow (“Wegsehen”) Head Shaking in the play and under Weed Ceremonies. Red-necked Grebe. I have seen slow Head The Rushing Display. In Rushing, Horned Shaking in the Great Grebe (Storer 196313: Grebes rise in a way similar to that of the 283), and I have observed more rapid Head Penguin Dance, but they orient side-by-side, Shaking in the Silver and Taczanowskis’ and move forward rapidly in the water. In Grebes. I have filmed Head Shaking in at this species, I have seen it only in connection least three different forms in the Western with the Weed Ceremony. Grebe: a rapid shaking in the Bob-Shake Dis- Rushing appears as a rare variant in the play, a slow turning in the Barging Display, Penguin Dance in the Eared Grebe (Mc- and Dip-Shaking. (The last two are described Allister 1958:295), and I once saw a pair of by Nero, in Palmer 1962:lOl.) Red-necked Grebes use it instead of the Pen- When, as in the case of the last species, guin Dance in a Discovery Ceremony. (This both fast and slow variants of Head Shaking case was unusual in that a third bird inter- occur in the behavior repertoire of a species rupted the ceremony during the Rushing.) and are used in different situations, I have There appears to be no record of Rushing by limited the term “Head Shaking” to the more Great Crested Grebes. rapid motion and have referred to the slower Rushing and the Penguin Dance seem to be one as “Head Turning.” The use of these very closely related. This is indicated by the terms is intended merely as descriptive; no similarities of the postures used, by the occa- homologies are implied. sional use of Rushing in place of the Penguin Rapid Head Shaking is thought to be de- Dance by Eared and Red-necked Grebes, as rived from the common head shaking comfort mentioned above, and also by the fact that movement used in removing dirt, water, etc., the Weed Ceremony of the Horned Grebe from the head and bill. (See McKinneys’ dis- involves Rushing whereas the Penguin Dance cussion [ 1965:135-1371 of this behavior in is used in the comparable displays of the Red- ducks. ) Whether Head Turning has the same necked, Great Crested, and Western Grebes. derivation is open to question. It may even The upright position on the water in both have arisen more than once. Dipping the bill these displays and in the Ghostly Penguin are in the water followed by raising and shaking characteristic of displays of high intensity. the head is a related and not uncommon com- Indeed, the height to which birds rise in the fort movement in Homed Grebes. This move- water in displays may prove useful as one ment is seen in a highly ritualized form in the means of estimating the intensity of the mo- Dip-Shaking Display of the Western Grebe tivation producing the display. ( Nero, in Palmer 1962: 101) . Although ritual- Head Shaking Display. In Homed Grebes, ization of this movement has not been re- this display, a rapid turning of the head from ported for any other grebe, I have seen it side to side, occurs rather frequently. One or used, probably as a displacement activity, by two Head Shakes are usually given as a pair Homed Grebes in aggressive situations. comes together for a Triumph Ceremony, Habit Preening Diqduy. This ritualized This display is most conspicuous in Head type of preening is a simple motion, the grebe Shaking Ceremonies and is also seen as a bringing its head down over the back and postcopulatory display. In this display, the running the bill through or near the feathers crests and tippets are usually somewhat of the back or wing. In Homed Grebes, it is spread, and the displaying bird may face a feature of the climax of the Discovery Cere- toward or away from the bird to which it is mony and high-intensity Head Shaking Cere- displaying, or the two may be side by side. monies. Head Shaking is a common type of display The term was coined by Huxley ( 1914:497) in grebes. Simmons ( 1955: 182) describes both in his work on the Great Crested Grebe and rapid and slow variants of Head Shaking in also discussed by Simmons ( 1955: 185-188) the Great Crested Grebe. Huxley (1914) used in his work on the same species. Mrs. McAllis- the term “shaking” for this display, which he ter (1958:293) describes under the same name later (1924) called “head-shaking.” In describ- a less localized preening by Eared Grebes. 194 ROBERT W. STORER

FIGURE 4. Tracings of a motion picture fihn of Homed Grebes showing the transition from Habit Preening to the Penguin Dance at the climax of a Discovery Ceremony.

Habit Preening has not been reported for the by Advertising, and appears to be set off by Red-necked or Great Grebes, but I have ob- one birds’ diving and then the seconds’ assum- served it in Silver and Taczanowskis’ Grebes. ing the Cat Posture. The diving bird then The latter two resemble the Horned and Great emerges in a series of Bouncy Dives. In the Crested Grebes rather than the Eared Grebe case of the Great Crested Grebe (Simmons in this display. Bob-Preening, an exaggerated 1955: 191) , the Cat Display or the Ripple Dive form of Habit Preening, is seen in the Western may come first. However, in the few com- Grebe (Nero, in Palmer 1962:lOO; personal plete records which I have of #theinitiation of observations). It is generally agreed that this ceremony in the Homed Grebe (made Habit Preening is derived from ordinary by two persons, each watching one bird), the preening. Cat Display was assumed after the approach- Weed Trick Display. A Horned Grebe dives, ing bird had dived and before it emerged in comes up with a beakful of aquatic vegeta- the Bouncy Posture. tion and, with head plumes spread, swims As the bird performing the Bouncy Dives toward a second bird. This display was de- moves past or around the bird in the Cat Dis- scribed and named by Huxley (1914:499-500) play and finally emerges in the Ghostly Pen- in his study of the Great Crested Grebe and guin Display, the latter raises its head, some- discussed by Simmons (1955:189-190). It is what as in Advertising. The bird in the also performed by the Red-necked Grebe Ghostly Penguin Display turns to face it, and (“Pflanzenbalz” of Wobus 1964:40; personal the

TABLE 2. Components of the Discovery Ceremony in six species of Podiceps.

Species gTi.wgena cristatus autitus nigricollis occipitalis taczanowskii

Cat Display Hunched Attitude + + Wing Spreading : : : : Display Dives Bouncy Dive + + + + + Porpoising Ripple Dive + : : Ghostly Penguin + + + + + + Climax Penguin Dance + Head Shaking : + : 1 : Habit Preening + Head Flicking : : Ending Turning-away + ? + + + Barging + : do not turn directly away from each other Huxley (1914:51%513) was the first to but swim more or less side by side. When describe this ceremony, which he called the they do this, the rigid posture is not relaxed “Ceremony of Discovery.” Simmons shortened and a Weed Display often follows. the name to “Discovery-Ceremony” (1955: 190). The Discovery Ceremony is performed in The studies of these two men on the Great spring usually prior to egg-laying. On the Crested Grebe, that of Wobus (1964:4647) breeding grounds, which the Homed Grebes on the Red-necked Grebe, and my own ob- often reach at least temporarily paired, it servations on the Red-necked, Eared, Silver, usually occurs when members of a pair have and Taczanowskis’ Grebes indicate that in its been separated for a long time or by a con- general pattern, as well as the circumstances siderable distance. Briefer separations more under which it is given, the Discovery Cere- often result in bouts of Head Shaking, from mony of these species resembles that of the which 1 would conclude that a Discovery Homed Grebe (,table 2). (Mrs. McAllisters’ Ceremony results from a more intense motiva- belief that the Discovery Ceremony of the tion than a bout of Head Shaking. I have seen Eared Grebe “is an incomplete form of the the Discovery Ceremony performed by birds penguin dance” [ 1958:295] evidently resulted along their migration route south of the breed- from her failure to recognize the full cere- ing grounds, and I suspect that it may also mony.) There are important differences among be performed before the birds leave their win- the species in the details of the ceremony. tering grounds. Although I have not to my The presence or absence of Spread-wing Pos- knowledge witnessed actual pair formation, ture in the Cat Displays and the different I suspect that Advertising followed by a Dis- types of Diving Displays have already been covery Ceremony is a prime factor both in mentioned. Even more striking are differences forming and later in strengthening the pair in the climax of the ceremony. Great Crested bond. Grebes simply have a bout of Head Shaking That a disturbance may also trigger a Dis- in the Upright Posture. Eared Grebes com- covery Ceremony is well illustrated by the bine the Penguin Dance with Head Shaking, following observation. On 28 April 1959 near and Red-necked Grebes combine it with Head Fort QuAppelle,’ a Red-necked Grebe left its Turning (slow swaying, Wobus 1964:46). mate in a large opening in a and swam Silver and Taczanowskis’ Grebes use the Pen- under a bridge to a large lake across a road guin Dance with varying combinations of from the marsh. At this point, R. W. Nero, Head Shaking, Head Flicking, and Habit F. W. Lahrman, and I drove up and s.topped Preening. The Great Crested Grebe appar- on the road between the two birds. Almost ently lacks a ritualized ending for the Dis- immediately, the bird on the marsh Adver- covery Ceremony, whereas the Silver Grebe tised loudly, and the other bird flew across may either Turn-away or Barge, and in my the road to it. The first bird assumed the Cat limited observations on Taczanowskis’ Grebe, Posture while its mate was still in the air and I have only seen Barging as an ending. Eared a Discovery Ceremony followed. and Red-necked Grebes use the Turning Away 196 ROBERT W. STORER like the Homed Grebe. In the Diving Dis- the actions of the Great Crested Grebe by the plays, the climax, and the ending of the cere- Ripple Dive during which the birds’ progress mony, the displays of the Silver Grebe are can be (and is) followed by its mate, and in far less fixed than are those of the northern the actions of the other three species by the species. Bouncy Display (derived from the agonis- If, as I suspect, the Discovery Ceremony is tically neutral act of bathing, quite likely a major element in the pair-formation process through its use as a displacement activity, and later serves to strengthen the pair bond, during this period when attack and escape it must provide a means whereby a bird will drives are balanced). It is particularly inter- find a mate of the same species and the op- esting in this connection to note that as the posite sex. Specific differences in the shape diver approaches the second bird, the dura- and color of the bill and the head plumes tion of ,the dives becomes shorter and the must be important in a grebes’ recognition of Bouncy Display more frequent, though of a member of its own species, as are also inter- shorter duration. Thus, as we would expect specific differences in the Advertising Call the impulse to flee would increase in the and in the details of the Discovery Cere- waiting bird as it is approached under the monies. The last can be likened to a maze water, we find the diving bird indicating its wherein a bird must make a series of correct position with greater frequency. Simmons responses to achieve a goal. The similarity (1955: 199) expressed the idea that the Ghostly of the sexes and the interchangeability of the Penguin emergence is “based on the move- roles in the Discovery Ceremony and other ments for attacking from under-water.” Un- courtship behavior make the question of how fortunately, we do not know what the under- a bird chooses a mate of the proper sex some- water postures of an attacking bird are, but what more difficult. The smaller bills and it is likely that the head is drawn back and overall size, the shorter ornamental plumes, not extended in the odd posture so character- and the slightly duller plumage of the females istic of the Ghostly Penguin, and of Rearing may be factors, but I suspect that the slightly and the Rushing Ceremony of the Western greater height of the males in displays which Grebe. Although I have no suggestions as involve the Penguin Dance may be the de- to how this display may have originated, I ciding one. These are questions on which ex- think it is highly significant that the bird per- perimentation and further observations would forming the display always does so while be most valuable. facing away from the second bird. Thus we In attempting to analyze the components can postulate that a balance or near-balance in the Discovery Ceremony, I am impressed in agonistic components is achieved by the by the apparent balance between attack and bird in the more defensive posture (Cat) fac- escape elements in the parts of the ceremony ing toward, and the bird in the more aggres- in which #the two birds use different displays. sive posture (Ghostly Penguin) facing away, In the case of mutual displays like the Pen- from the bird with which it is performing the guin Dance, a balance is maintained largely ceremony. From this point on in the cere- by the similar actions of the two birds, a mony, the two birds perform the same dis- small sexual component being responsible for plays, but it is worth noting that ,the more counteracting such minor differences as the aggressive postures are used when the birds relative heights of the birds ’ heads. I do not are face to face and the more appeasing ones believe that early in the cycle when the Dis- when the birds turn away. covery Ceremony starts, the sexual component Head Shaking Ceremony. Two Homed can be strong enough to overcome any but Grebes meet face to face and start a series minor differences in aggressive components of rapid Head Shakes. The ceremony may during this ceremony. To me the Cat Display end with but one or two shakes by each bird, is best described as derived from a defensive or Head Shaking may gain in intensity until act. The feathers and wings are spread to the birds rise in a Penguin Dance, in which increase the birds’ apparent size and the head case Habit Preening usually follows. Very is drawn back to a position from which a high-intensity ceremonies may be followed by thrust of the beak can be made. The dives Ceremonial Turning Away and a Weed Rush. made by the approaching bird are very likely, Head Shaking Ceremonies may occur in as Simmons (1955:199) suggests, “a form of situations which might set off a Discovery symbolic‘ ’ attack.” However, the “dangerous” Ceremony but in which the motivation is not element of the act, that is, the diving birds’ as strong. They become more frequent for a being hidden from view, is counteracted in time after pair formation, as the pair bond BEHAVIOR OF THE HORNED GREBE IN SPRING 197

i / -___-

F E

FIGURE 5. Part of a Weed Rush by Homed Grebes.

becomes stronger, and they are in turn used and Bob-Preening are used in the comparable less frequently as the nest becomes the center ceremony of the Western Grebe (personal of attention of the pair. The similarity of the observations), but in this species the birds second part of this ceremony to the Discovery most often swim side by side during the cere- Ceremony suggests a close evolutionary rela- mony. As in the Head Shaking Ceremonies tionship between them. They differ, however, of at least the Horned and Great Crested in that Head Shaking Ceremonies appear to Grebes, Head Shaking (Bob-Shaking) is reg- start at a low intensity, which may increase ularly followed with a form of Habit Preening through the first part of the ceremony, whereas ( Bob-Preening), and indicates an approach- there appears to be much more tension at the ing end to the ceremony. start of a Discovery Ceremony. Head Shaking Weed Ceremonies. If both members of a Ceremonies also differ from Discovery Cere- pair of Horned Grebes perform the Weed monies in that the roles of the two birds are Trick at nearly the same time, a Weed Rush the same throughout, the “symbolic” attack usually ensues. The birds, coming together, and retreat of the first part of ,the Discovery turn and Rush side by side for a few to per- Ceremony being replaced by Head Shaking. haps 30 ft. Then they move apart, move to- This, and the use of Head Shaking Ceremonies gether and Rush, move apart, and so on. Suc- when a male returns to his mate after driving cessive Rushes may be in the same or in dif- off an intruder, suggests that the aggressive ferent directions. Sometimes the birds Rush element in Head Shaking Ceremonies is back and forth, while at other times the direc- weaker than that in Discovery Ceremonies. tions of the Rushes appear to be random. The Head Shaking Ceremonies are reported in number of Rushes in a ceremony varies from the Great Crested Grebe (Simmons 1955: 184- one to 10 or more and is usually at least four 189), the Eared Grebe (McAllister 1958:293- or five. The ceremony ends when one or both 294), the Red-necked Grebe ( Wobus 1964: birds drop the weeds. As the birds separate 39-40), and the Great Grebe (Storer 196313: at the end of each Rush, they subside into the 283). What Mrs. McAllister ( 1958:294-295) Upright Posture and often swim about briefly described as the “Penguin Dance” probably before coming together for another Rush, again includes high-intensity Head Shaking and Dis- rising to the Penguin Posture as they meet covery ceremonies; the relationship ,to Weed and Rush (fig. 5). If one bird comes up with Ceremonies in this species is not clear. The weeds before the second dives or if both dive more exaggerated motions of Bob-Shaking and only one comes up with weeds, the bird 198 ROBERT W. STORER with weeds usually swims about for several conflict like this could evolve into part of the seconds before dropping the weeds in the courtship ritual. water. On rare occasions, the second bird may dive after the first has come up with weeds, PLATFORM BEHAVIOR may also come up with weeds, and join the Inviting, As I have pointed out earlier first bird in a..W@@,Rush. Occasionally, if one (Storer 1963a), the precopulatory behavior of bird fails to .bring up weeds, both may dive all grebes, so far as known, is quite similar. again and,-both bring up weeds, and a Weed Of the three soliciting displays, Inviting, Rear- Rush may ensue. Usually, however, synchrony ing, and Wing-quivering, the first is the most in the Weed Trick appears a requirement for frequently performed. Even before a plat- the Weed Rush. form is built, a Horned Grebe may Invite on In the Great Crested, Red-necked, and the water, putting the head forward just over Western Grebes, the Weed Ceremony is -per- the surface and flattening the nuptial plumes. formed as a Penguin Dance rather than a The neck is kinked so that the head is lower Rush. In fact, it was called the “Penguin than the posterior end of the neck, After a Dance” by both Huxley (1914) and Simmons platform is built, the birds usually Invite on ( 1955, 1957). I prefer to use the term “Weed it, and in doing so, they usually hold the head Dance” for this ceremony and to limit the lower than the body. The Inviting posture is term “Penguin Dance” to similar ceremonies also that of the “passive” bird during copula- in which no weeds are carried (see below). tion. Hosking and Newberry (1946) published Simmons (1965) now also uses this termi- photographs of female (ph. 73-75) and male nology. (pl. 77) Horned Grebes Inviting. These photo- Weed ceremonies were probably derived graphs were published earlier, but with less from nest-building activities. Two observa- successful reproduction, by Hosking ( 1939). tions on Horned Grebes support this view. Huxley ( 1914:502) referred to the corre- I once saw a pair of these birds, each carry- sponding display of the Great Crested Grebe ing nesting material, approach their partially as the “passive pairing attitude,” and Simmons built nest from the same side. As they came (1955:243) called it the “invitation-display” near each other, they rose part way out of the or “inviting.” I prefer “Inviting” as the simpler water and Rushed to the nest on which they of Simmons ’ terms, both of which have the then deposited the material. On another oc- advantage over Huxleys’ in indicating the casion two birds performing a Weed Rush soliciting function of the display. The illus- chanced to end the ceremony near their nest, trations in Simmons ’ paper (1955:244, 247), whereupon they deposited the weeds they show the Inviting bird with the neck straight were carrying on it. If, as these observations out, but the photographs in a later paper suggest, the Weed Rush was derived from (Simmons 1965:22S ) show ,the neck kinked, nest-building activities, ,the Weed Dance was somewhat as in the Horned Grebe. Inviting is probably derived from the Weed Rush rather essentially similar in the Red-necked (Wobus than the reverse. A hypothetical evolutionary 1964:49-53; personal observations), Eared, sequence of displays might be: obtaining and and Silver Grebes. The copulatory behavior carrying nesting material, Rushing side by of Taczanowskis’ Grebe has not been de- side (the addition of sexual and/or hostile scribed but doubtless is similar to that of the motivation), standing face to face in the Silver Grebe. Weed Dance, performing the Penguin Dance I have seen a male Horned Grebe Inviting (without weeds), and finally the use of the on the water near a clump of emergent vege- Penguin Dance in new ceremonies. The first tation and then nest-building by both mem- two phases may be seen in the behavior of bers of the pair at the same place. From this the Horned Grebe as described here, the third I infer that Inviting is also associated with may be seen in the Weed Dances of the Great selection of a nest site. Inviting and building Crested, Red-necked, and Western Grebes, may occur at several sites before the final one the four.th in the Penguin Dance of the Eared is selected. Male Western Grebes use the Grebe, and the fifth in the use of the Penguin comparable Inviting Display (Low Arch) in Dance as a component of the Discovery Cere- similar situations. mony in all but the Great Crested Grebe. A Rearing. A Homed Grebe Inviting on a different view, that the Penguin Dance was platform may rise to its feet, kinking its neck derived from breast-to-breast battle, has been and holding its head downward at an angle expressed by Wobus (1964:45), but I find it of approximately 45”. The crests and espe- difficult to understand by what means active cially the tippets are spread and flared out. BEHAVIOR OF THE HORNED GREBE IN SPRING 199

FIGURE 6. Platform behavior of the Homed Grebe and related species. A. Rearing, B. Wing-quivering, and C. Inviting, (all Horned Grebes). D, E, and F. Rearing by Eared, Red-necked, and Great Crested Grebes, respectively, (the last after an outline drawing by Robert Gillmor from a photograph by W. N. Charles ) .

This attitude is maintained rigidly, unless which show that the display in these species interrupted by Wing-quivering, for several is essentially similar to Rearing in the Horned seconds, after which the displaying bird usu- Grebe (fig. 6). ally resumes Inviting. This soliciting display The derivation of Rearing is not clear. Mrs. is less frequent than Inviting and more fre- McAllister ( lot. cit. ) suggested that it may quent than Wing-quivering. It also appears be “the ritualized intention movement of sit- to be intermediate between these two displays ting down on the nest.” She also pointed out in intensity, Inviting being the least and Wing- resemblances to the posture of the active bird quivering the most intense form of soliciting. during copulation and the posture used when A pho,tograph of a male Horned Grebe Rear- turning the eggs. As I have pointed out earlier, ing appears in Hosking and Newberry ( 1946: the odd posture of the head and neck in Rear- pl. 78), but the authors do not comment on it ing resembles that in the first phase of the as a display. Ghostly Penguin Display and in the Western Simmons ( 1955:244-246) described Rearing Grebes’ Rushing Display. in the Great Crested Grebe and appears to Wing-quivering. While Rearing, a Horned have coined the term. He also summarized Grebe may suddenly raise its body to a more the earlier accounts of this display. His figure nearly vertical position, at the same time keep- (p. 245) does not represent the usual form of ing its head down, and quiver its nearly closed Rearing, which is shown in his later paper wings rapidly, usually showing the white in (1965:228) and still better in a photograph the secondaries. After Wing-quivering, the by W. N. Charles from which an outline draw- bird may continue Rearing or may subside ing has kindly been prepared for my use by into the Inviting posture. Robert Gillmor. Wobus (1960:62) figured This most intense form of soliciting has Rearing by the Red-necked Grebe, but he did been well discussed by Simmons (1955:246) not show the characteristic kink in the neck. and like the other soliciting displays is prob- Hanzik ( 1952: 16) mentioned that Eared ably essentially similar in all grebes. I have Grebes “use this peculiar position” (Rearing), recorded it in the Red-necked and Eared but Mrs. McAllister ( 1958:301) stated that she Grebes, as well as in the Great ( Storer 1963b), did not observe it. I have motion pictures of Pied-billed (McAllister and Storer 1963)) and Rearing by Eared and Red-necked Grebes, Wes, Grebes. This display may be derived 200 ROBERT W. STORER from the “wing-shake,” which in my experi- “AAANRRH.” As Advertising appears to be ence is a rather rare comfort movement in the first step in pair-formation, it is important grebes. that the accompanying note should be species- Copulation and msociated displays. In the specific. Because it is later used as a location Horned Grebe, I have only observed copula- note, individual recognition is also important, tion on platforms built by the birds. These although more so in species like the Eared platforms are not necessarily those subse- and Western Grebes, which nest in colonies, quently used as nests or even in the pothole than in the more solitary Homed Grebe. The on which the birds eventually nest. Before accompanying sonagrams (fig. 7) show that and during copulation the passive bird re- the call is a single no.te, usually descending in mains in the Inviting posture. The active bird pitch and ending in a rattle or harsh trill. As moves about behind the passive bird for some can also be seen from the sonagrams of Ad- time before mounting. It may make a variety vertising calls of four different birds, there of motions, including comfort movements, is considerable variation in the length of the head-bobbing, and the “display” shown by note, in the relative lengths of the rattle and Hosking and Newberry (1946:pl. 76, p. 112); the rest of the note, and in the timbre of the but to date, I have not been able to discern voice, as shown in the number and strength a regular pattern for such motions. Mounting of the overtones. These notes are usually given is immediately preceded by Copulation Trills, in bursts of several calls, the intervals between which are continued, with increasing intensity, the calls usually being between one and two by the active bird until just before it dis- times the length of the call. The individual mounts, waddling over the head of the pas- calls in a burst may vary somewhat, but prob- sive bird and paddling rapidly as it slowly ably not in any regular pattern. (A burst of subsides into the Upright posture. Mean- six consecutive calls is shown in fig. 7.) while the passive bird raises its head and the The Advertising call of the Great Crested two may give one or two quick Head Shakes. Grebe has been described by Simmons (1954: The active bird may preen a bit and turn 53) as “a loud, drawn-out grr-owp‘ ’ . . . fol- toward its mate. This may be followed by lowed by a secondary no,te, a moaning purr, a few Head Shakes and preening by both row-ah‘ .”’ Mrs. McAllister has rendered that of birds. The postcopulatory behavior appears the Eared Grebe (1958:291) as “poo-eee-chk,” to be rather variable. from which it is easily recognized in the field. Reverse mounting occurs not infrequently (Sonagrams of this call are shown in fig. 7.) In early in the cycle of platform behavior; later, the Silver Grebe, I have recorded the Adver- it is rare. I have recorded it in at least the tising call in my notes as “chaok” and noted Horned, Eared, Red-necked, Western, and that upon closer hearing, it might prove to be Pied-billed Grebes. more complex. Taczanowskis’ Grebe has a According to Simmons (1955:248), Head similar note, but I did not hear the two species Shaking, with the active bird in front of and near enough in time to make a meaningful facing away from the passive bird, is a regular comparison. feature of the postcopulatory behavior of the Platform call. While at or near a platform, Great Crested Grebe, although the length of Homed Grebes frequently give a two- or three- such Head Shaking Ceremonies is quite vari- syllable call which I transcribed in my notes able. Wobus (1964:49) described and figured as “ga ga.” Often when one bird is off for- (fig. 27, p. 52) a postcopulatory pose of the aging, its mate may remain near the nest giv- Red-necked Grebe which he termed an ec- ing this call repeatedly for several minutes at static posture. This, he says, is followed by a time. This call is also given while a bird is slow Head Shaking (“Wegsehen”). I have a Rearing or Inviting and by the passive bird film sequence taken in Saskatchewan showing during mounting. Both males and females use the same displays. I also have a sequence it, but I think males use it more frequently showing Habit Preening after reverse mount- and give the call more loudly than females. ing in the Eared Grebe. Rapid postcopulatory The intensity with which the call is given water treading appears to be usual in all varies considerably. As the bird becomes more species studied. excited, this note grades into a loud, - like honking note, which may function, at SOME VOCALIZATIONS least in part, as an alarm call. (This transition OF THE ADULTS is illustrated in fig. 8.) Advertising call. The Advertising call of the On at least one occasion, I heard a male Horned Grebe consists of a single syllable, give this call while Inviting on the water at to which I have referred in my notes as a place where shortly later he and his mate BEHAVIOR OF THE HORNED GREBE IN SPRING 291

2

1.0 2:o

FIGURE 7. Advertising calls of Horned and Eared Grebes. Two top rows: a burst of six calls given by a Homed Grebe near Bethany, Manitoba, 11 May 1967. (Th e intervals between calls ranged from 0.3 to 0.6 sec.) Third row, left and center: two calls of a Homed Grebe recorded near Minnedosa, Manitoba, 11 May 1967; and right: a Homed Grebe recorded near Fort QuAppelle,’ Saskatchewan, 16 May 1966. Bottom row, two left calls: a Horned Grebe recorded near Moline, Manitoba, 14 May 1967; and two right calls: Eared Grebes recorded at the Lower Souris National Wildlife Refuge, North Dakota, 26 June 1965. 202 ROBERT W. STORER

2

4

2

1.0 2.0 SECONDS

FIGURE 8. Calls of the Homed Grebe. Top row: Platform calls. Second row: transition from Platform calls to single honk-like note. Third row: Duet trill. Bottom row: Copulation trill. BEHAVIOR OF THE HORNED GREBE IN SPRING 203 did some building. Thus, it may be part of dependently more than once. This implies the behavior involved in selecting a platform close relationship of these species, which is site. borne out by the pattern of *the downy young This call apparently directs the mates’ at- (Storer 1967). These six species can be di- tention fo both the bird which is calling and vided into those which use weed ceremonies the place whence .it is calling. In contrast, (Homed, Red-necked, and Great Crested) and the Advertising call directs another birds at- those in which such ceremonies are unknown tention solely to the calling bird. I have re- (Eared, Silver, and Taczanowskis).’ The pat- corded a male Red-necked Grebe giving a terns of the downy young also confirm

STORER, R. W. 1963a. Courtship and mating be- TINBERGEN, N. 1953. The Herring Gulls’ world. havior and the phylogeny of the grebes. Proc. Collins, London. XIII Intern. Omithol. Congr., Ithaca, p. 562- WETMORE, A. 1924. Food and economic relations 569. of North American grebes. U. S. Dept. Agr. STORER, R. W. I963b. Observations on the Great Bull. 1196. 23 p. Grebe. Condor 65279-288. WOBUS, U. 1960. Nestbau und Balz des Rothals- STORER, R. W. 1967. The patterns of domwnygrebes. tauchers. Vogelwelt 81: 61-62. Condor 69 :469478. WOBIJS, u. 1964. Der Rothalstaucher (Podiceps TINBERGEN, N. 1951. The study of instinct. Oxford griseigenu Boddaert). A. Ziemsen, Wittenberg Univ. Press, London. Lutherstadt.