Territorial behaviour of wild at Delta, Manitoba

NORMAN R. SEYMOUR

Territory typically refers to ‘any defended area’(Hinde, 1956) and this usage is adhered to in this paper. The status of territory in breeding is less clear than in most other . Hochbaum (1944) considered it to be present in all dabbling ducks, but Sowls (1955), Dzubin (1955) and Lebret (1961) did not agree. In the Anas clypeata, published accounts are conflicting. Hori (1963) con­ cluded from his studies of wild Shovelers in Kent, England, that they were non­ territorial. Poston (1968) also found little evidence for territorial behaviour near Strathmore, Alberta. However, McKinney (1967), in agreement with Hochbaum (1944) and Sowls (1955), presented evidence, based mainly on intensive studies of captive birds, that territorial behaviour can be well de­ veloped. Detailed data relating to this be­ haviour in wild populations appears to be lacking. The present study was designed to obtain such quantitative data on the manner in which areas are defended, and the extent to which such defended areas, as opposed to the undefended portions of the home range, are used by pairs of Shovelers. D ata were also collected on the types and frequencies of hostile male behaviour involved in territorial defence.

Study area Figure 1. Number of Shovelers present and engaged in different activities during successive The study area lay 2-4 km south of Delta, weeks during breeding period (20 April-10 July). Manitoba, and was a roadside ditch, 1-9 km long and 10-20 m wide, together with por­ of it by week 7. Except for 0-2 km at the north tions of adjacent meadows. The general fea­ end, the ditch was never clogged with vegeta­ tures of the area in 1970 were essentially tion, although Typha sp., Scirpus spp. and unchanged from a description given by Sowls Phragmites sp. did appear in discontinuous (1955). A 12-week period of observation, 20 patches along the sides of the ditch through­ April to 10 July 1970, encompassed all known out the summer. Shoveler breeding activity on the area (Figure 1). Methods The ditch and water on the adjacent east meadow were connected during the first 8 Seventeen males were trapped by placing a weeks of observation. The meadow water hand-reared captive female in a clover trap decreased progressively, however, from of the design described by Lincoln & Baldwin 26-8 ha (67 acres) during week 1, to 0-4 ha (1929). They were marked with nasal saddles (1 acre) during week 8. The ditch proper, (Bartonek & Dane, 1964) and released at the which became distinct from the drying mea­ trap site. Mated males were caught by plac­ dow during week 9, contained water ing the trap at the male’s major loafing spot throughout the summer, and was crossed by on the ditch ; unmated males were captured four small dykes. in the meadow. In addition, three females Vegetation of the flooded meadow began were caught on their nests, similarly marked to emerge during week 5 and covered much and released. 49 50 Norman R. Seymour

A car was used to observe the area at the one nest on the study area was destroyed northern and southern limits of the study by predators and most pairs left the area. area, a 6-m observation tower near its centre. No new territories were subsequently Wooden strips were placed at 30-m intervals established. out from the major loafing spots of males, and at 90-m intervals on the meadow, to enable the location of males to be estimated. Aggressive behaviour and territorial defence The first count was normally made as soon as the birds could be seen (approximately Direct observations of localized aggressive 05.00 hours) and lasted for 30 minutes. Sub­ behaviour concerned, primarily, ten marked, sequent counts of the same duration were paired males. Additional supporting evi­ done at 2-hour intervals, the last being just dence for territoriality was provided by prior to dark (approximately 22.00 hours). observations of‘ritualized fighting’ (McKin­ This schedule was followed for 4 or 5 days ney, 1967), mainly at the apparent boundaries each week, except the first and last, when it of defended areas. was reduced to 3 days. Aggression in Shoveler males includes In addition, weekly aerial transects of the ‘hostile pumping’ (threat display), ‘ritualized marsh were made from 6 May to 13 July fighting’, ‘chasing’, and ‘three- flights’ and intensive checks of the water areas at the (see McKinney, 1967, 1970 for descriptions periphery of the marsh were made every 2 of these behaviours). The last named are weeks from 1 May to 1 July to determine referred to throughout this paper as pursuit where Shoveler territories occurred. flights. ‘Hostile pumping’ and associated calls were elicited in a resident male when an Breeding chronology intruder approached the defended area. If the intruder continued into the territory, Paired Shovelers began to use the flooded ‘hostile pumping’ was followed by ‘chasing’, meadow during week 1. These pairs were then pursuit flights if the intruder did not non-aggressive upon arrival and often sat immediately leave the area. ‘Hostile pump­ within 1-5 m of other pairs. Poston (1968) also ing’ and calling were also noted, in the found that newly arrived Shoveler males apparent absence of other Shovelers, when showed little hostility. Male threat display the male returned to the defended area after increased during week 2, being based on a pursuing intruders. At these times, he typic­ ‘moving territory’ (Dzubin, 1955), in which ally sat in the ditch near his loafing spot for the male defended the mobile female. During 5-10 minutes or longer, often vocalized, and week 3, aggression increased further and then went to the loafing spot. ‘Hostile pump­ pairs became isolated from each other. ing’ was also seen when a male approached Unmated males arrived during week 2 a neighbouring territory whether or not the (Figure 1). They courted and chased mated resident male was there. females and made jump flights as described ‘Chasing’ was done primarily by territorial by Lebret (1961) and M cKinney ( 1970). F rom holders, who typically rushed over the water one to seven unmated males would harass a with the neck outstretched and bill slightly pair, whose male threatened and chased the upward, often open, and pointed at the other intruders. During week 3, of seventeen pairs male. The latter, usually unmated, showed under observation, twelve began searching little hostility toward the chaser and gener­ for nest-sites on the ditch. Unmated males ally left the area quickly. ‘Chasing’ usually remained on the flooded meadow at that gave way to ‘ritualized fighting’ between time, rarely harassing pairs which were using holders of contiguous territories (see below). the ditch. In the Shoveler pursuit flights appear in Figure 1 also indicates the number of pairs part to function in driving away intruders, on the study area that were considered ‘terri­ and hence do seem relevant to territorial torial’ and ‘non-territorial’ on the basis of defence. evidence presented below. Twelve different Aggressive interactions were highly pairs resided on the study area over the 12 localized, occurring mainly in the vicinity weeks, the last pair having established them­ of the loafing spot. Table 1 indicates the fre­ selves during week 10. Non-territorial pairs, quency of male sightings and of aggressive apparently searching for suitable breeding behaviour of resident males in relation to the sites, were present for periods ranging from loafing spot during the entire laying and in­ 2 days to 3 weeks. There was an influx of cubation periods. There were significantly non-territorial pairs in weeks 8, 9 and 10 more sightings and hostile encounters close (Figure 1). During week 10 and 11, all but to the loafing spot (0-30 m) both for the com- Territorial behaviour of wild Shovelers 51

Tabic 1. Location of marked territorial males on their territories and of aggressive interactions between these inales and intruders relative to the major loafing spot used

Distance from major loafing spot

30 m 31-60m 61-90m

Location of spot sightings of 10 399 (83%) 34 (7%) 48 (10%) males (481 sightings) Location of males during bouts of 117(93%) 6 (5%) 3 (2%) observation (126 hours) Location of aggression (threat, 257 (73%) 89 (25%) 8 (2%) chasing, ritualized fighting) of 10 males Location of boundary conflicts 5(16%) 24 (71%) 4(13%) bined data on nine males (y_2 = 88, P < 0 001) each bird on its own territory. ‘Hostile pump­ and for an additional single male (y2 = 212, ing’, ‘chasing’ and occasionally ‘ritualized P< 0 -001). fighting’ occurred primarily when one male The male was most visible to, and best approached more closely to the other or seen by, intruders from either the prominent crossed the common boundary. Such inter­ loafing spot or from the unbroken expanse actions by males with laying or incubating of ditch. Most intruders approached along females typically occurred immediately after the ditch and rarely from the meadow behind. he had accompanied his mate to the nest-site Almost all (95%) hostile displays occurred and returned to the ditch. However, most either at the loafing spot or in the ditch, boundary interactions occurred during the suggesting that the water area rather than pre-laying period, the time of territory the meadow area was being defended. Prior establishment. After the initial boundary to pursuit flights, the pursuer was usually interactions, the neighbour’s territory was on or near the loafing spot. After 264 (99-2%) rarely entered whether or not the owner was such flights, the pursuer returned to the terri­ present. Where boundary conflict had inti- tory, usually within 30 m of the loafing point, ally been intense, territorial males did not which further indicates that aggression was enter contiguous territories even after the territorial in function. Pursuing males whose neighbouring male had deserted. mates were at the nest returned to the terri­ Extensive observations (96 hours) of four tory on 188 (95-5%) occasions, suggesting neighbouring males which established terri­ that the behaviour is related to the physical tories at approximately the same time, pro­ site and not just the position of the female. vided additional information about terri­ Vocalizing by the female at the nest was not torial boundaries. The territories of these detected during or after pursuits but this males (A-D) during the pre-laying period are may have occurred and influenced the male’s illustrated in Figure 2. Although it is difficult return. to define exactly the location of boundaries Hinde (1966) indicated that, ‘along the where actual conflicts were not seen, the boundary between territories is a narrow no­ dashed lines delineate them approximately, man’s land where prolonged skirmishes take on the basis of disputes that were seen (dots place and actual combat is rare, such skir­ in Figure 2) combined with the almost exclu­ mishes being practically limited to the sive use by the resident male of the remaining boundary region’. ‘Ritualized fighting’, which area. More than 70% of encounters at the appears to be an example of such skirmishes, northern boundary of the territory of male A was used by McKinney (1967) to indicate and southern boundary of the territory of the location of Shoveler territorial bound­ male B involved unmarked males, presum­ aries. As indicated in Table 1, most ably attempting to establish territories. Over ‘ritualized fighting’ in the present study 90% of encounters occurred on the ditch occurred in the area of 45-60 m from the itself, apparently because most intruders loafing bar (y2 = 25-7, P < 0-001). landed there. Males on contiguous areas appeared to Pursuit flight endings are also included in recognize common boundaries. They were Figure 2. They indicate that pursuits typic­ to be seen sitting, relatively inactive, for as ally ended near, but outside the territory as long as an hour within 3-6 m of each other, defined by boundary conflicts per se. Pursuit 52 Norman R. Seymour

Figure 2. Coincident territories of four Shoveler males (A-D) along a roadside ditch. ----- , Limit of area intensively used and defended; • , disputes between Shoveler males; x, nest of resident female; O, loafing spot of resident male; A> A, V, end of pursuit flights made by males A, B, C, respectively. flight behaviour between males A and B also a vertical component to territory size. provided further evidence that neighbouring Defending males would threaten intruders males recognize and observe a common at more than 90 m (height estimated by com­ boundary between their contiguous terri­ parison to power line poles) but rarely gave tories. These flights typically involved re­ chase unless the intruder indicated the inten­ versal of roles, the pursuer becoming the tion to land. pursued, when crossing above the boundary Dzubin (1955) observed that territories in line in the ditch. the Mallard Anas platyrhynchos and Blue­ winged Teal Anas disoors may be larger during the early periods of nesting. A sig­ Territory size nificant difference (x2 = 13-0, P < 0-001) was also found in the mean area used by Shovelers Estimates were obtained of the maximum before and after the onset of egg-laying space defended, actually only a very restricted (Table 2). Observations of three Shoveler portion of the total home range used by the males whose mates retained eggs for a con­ pair (Dzubin, 1955). This was illustrated by siderable time revealed that defence was territorial males which at times range far on strong until it ceased abruptly during late pursuit flights. incubation. As shown in Table 1 all defence during Territorial males ranged farther from the the laying and incubation periods occurred loafing spot during the early-morning (05.00— within 90 m of the loafing spot, thus making 10.00 hours) period, apparently because, the maximum effective size of the territory aggressive interactions, particularly pursuit approxim ately 0-9 ha (Table 2). There was flights, were triggered at this time by the’ Territorial behaviour of wild Shovelers 53

Table 2. Comparison of maximum size on the territory was based on first and last (hectares) of territories between the sightings of the male or female of the pair; pre-laying and laying/incubation duration of a male’s dominance was based periods of ten Shoveler pairs on his success in excluding others. The importance of the nest was suggested Pre-laying Laying/incubation by the almost immediate reversal in domin­ ance between males 2 and 1 following nest Mean area 2-9 0-9 loss by pair 1. Dominance may also alter Median area 3-2 0-6 prior to nest loss, however, for male 3 Range in area 1-3-5-0 0-1—1-5 assumed dominance over male 2 about 10 days prior to the loss of the latter’s nest, when the pair-bond was weakening and male increased movement of non-territorial pairs. 2 was spending much less time on the When non-territorial pairs were active later territory. in the day, the same phenonemon was The use of the territory by the female may observed. Despite the temporal variations in be severely restricted by the hostile behaviour aggression, territories did not change sig­ of encroaching males. Female 2 did not for­ nificantly in size as a function of time of day. sake the territory for at least 6 days after her Dzubin (1955) again reports a similar result mate deserted her, but she was extremely for the Mallard and Blue-winged Teal. secretive when off the nest, staying primarily There was no significant size difference in the vegetation in the ditch edge, and using between four territories established before only a few square metres of water opposite 8 June and five later territories, despite the the nest for feeding. Female 3 also used the fact that the concentration of both territorial territory after her mate deserted her, but and non-territorial pairs on the study area loafed and fed within a smaller area, approxi­ was then greater. This suggests that terri­ mately 15 m in radius, than she used before torial males do not occupy the largest pos­ her mate’s departure. A similar restricted sible area when pressure from other pairs is radius of activity was also noted for the only low. However, the concentration of pairs on other two females whose nests were still the study area was not sufficiently great to viable when they were deserted by their determine this point conclusively. mates. These observations suggest that the male is essential in maintaining the territory Stability of territories for the female.

Major changes in boundaries did not occur when adjacent territories were abandoned Use of territory due to nest failure. Stability was also main­ tained despite frequent hostile encounters In agreement with Poston’s (1968) work on between the territorial Shovelers (19% of all wild Shovelers, I found that pairs spent much encounters observed), and between non­ of their daylight hours on the territory. Dur­ territorial Shovelers and the incumbents. ing the pre-laying period, when the territory Poston (1968) similarly noted that once was being established, ten pairs spent from established, Shoveler pairs were not dis­ 2 to 4 hours on the territory (usually in the placed by other pairs. period 05.00-09.00 hours) when other pairs Certain areas were used by successive searched for nesting sites. They were not on pairs, rather than being occupied continu­ the study area at other times. During late ously by a given pair throughout the entire laying and incubation, males of ten pairs breeding season. One striking example of observed spent an average of 73-5% (range successive use of a portion of the study ditch 55-90%) of the daylight hours on the terri­ by three males is indicated (Table 3) in rela­ tory, thus making use of the area by other tion to egg laying and nest losses. Duration pairs virtually impossible.

Table 3. Use of the same portion of the ditch by three Shoveler pairs at different times

Duration of pairs First egg to on territory nest destruction Period of dominance

Pair 1 27 Apr .-27 May 15 May-22 May 27 Apr.-23 May Pair 2 15 May-17 June 1 June-16 June 24 M ay-6 June Pair 3 6 June-9 July 12 June-9 July 8 June-9 July 54 Norman R. Seymour

F emales spent all of the daylight period on ney ( 1965), however, believed that hostility in the territory, even in the absence of their the form of aerial chasing, as is seen in the mates. Hochbaum (1944) suggested that Shoveler, served to produce some degree of females may not have observed territorial dispersion of pairs. In agreement with boundaries at such times, but their activities McKinney, my data indicated that Shoveler were none the less localized, usually around pairs at Delta were spaced both in time, as the loafing spot. Such females were rarely seen in the nesting delay of non-territorial harassed by territorial or non-territorial pairs (Table 3), and in space as a result of males presumably because these males still territorial behaviour. associated the area with a hostile territorial Several hypotheses to explain the function male. of spacing in ducks have arisen. Hochbaum (1944) theorized that it ensured successful copulation, while McKinney (1967) sug­ Discussion gested that it was probably an anti-predator device (see also Erringt on. 1946; Tinbergen. Since Hochbaum (1944) reported territorial 1939). H ochbaum , M cK inney and W ard behaviour in ducks, several authors have (Delta Seminar, 1969) also stressed the im­ criticized aspects of Hochbaum’s conclusions portance of food to breeding ducks, as did while others state that territorial behaviour Geyr (1924) for the Mallard and Siegfried does not occur in the Mallard and Shoveler (1968) for the Southern Black Anas (Lebret, 1961 ; H ori, 1963). These differences sparsa. of opinion are considered by McKinney In the Shoveler, although territorial be­ (1965) to be due primarily to the dearth of haviour does appear to ensure protection evidence for defended areas. However, for for the female from aggressive males, this may the Shovelerand some other species, McKin­ be little more than a secondary consequence ney (1965) and Siegfried (1968) state that the of territory, as discussed by Hine (1956). concept of territoriality is valid and widely Spacing to reduce predation (McKinney, accepted. In agreement with McKinney’s 1965) seems reasonable and cannot be ruled (1965,1967,1970) work on captive Shovelers, out by the present data. Some resource my observations of localized activity (Figure essential to reproductive success may be de­ 2) including intraspecific hostility (Table 1) fended, thereby justifying the considerable and exclusiveness of the localized area, all expenditure of energy by the resident male show that Shoveler males in a wild popula­ in maintaining the territory. Broods of dab­ tion may defend an area which is often con­ bling ducks are very mobile (Evans & Black, tained within reasonably well-defined limits. 1955), and presumably feed little or not at Poston ( 1969), w orking in a prairie pothole all on the territory. However, the adult female habitat where the concentration of breeding may feed there exclusively during the later pairs was low, found home range size of stages of laying, and for the entire incubation Shovelers to be 73 acres (29-2 ha) while Gates period because they spend little time off the ( 1962), who worked in habitat similar to that nest (Ward, 1969). Certainly the laying and found at Delta, measured home ranges of incubating female Shovelers in the present not greater than 20 acres (8 ha). Mean terri­ study fed for much of their time off the nest. tory size during the laying and incubation The territory then appears to provide a mea­ periods in the present study, 2-3 acres (0-9 ha), sure of protection for the contained food closely resembles Poston’s (1969) estimate, resource and allow the female to utilize it based on two pairs, of 1-5 acres (0-6ha) for undisturbed. If so, this would seem to be a the corresponding ‘core area’. It seems likely reasonable functional explanation for the that this confined area, which is not readily extended and well-developed territorial be­ reduced byaggressive behaviour of intruders, haviour and pair bond of this species. must be considered the portion of the home A further possibility is that an extended range most crucial to reproductive success. pair-bond and associated territorial be­ haviour might be especially important to Shovelers during re-nesting. Competition for Functional significance of territory territory sites was keen at this time because of drying of habitat and influx of new pairs. Gates(1962), working with the Gadwall Anas Those which were able to establish territories streperà, and Poston (1968), working with nested quickly, whereas the females of two the Shoveler, discounted hostility, a com­ non-territorial pairs did not nest at all. ponent of territorial behaviour (Tinbergen, 1957), as a m echanism lim iting density of breeding pairs on their study areas. McKin­ Territorial behaviour of wild Shovelers 55

Acknowledgments season partly as a consequence of widespread nest predation. This study was supported by the National Re­ Aggressive behaviour of territorial males took search Council of Canada, the Manitoba Depart­ several forms and contributed to the establishment ment of Mines, Resources and Environmental and maintenance of territories. Such behaviour Management, and the Delta Waterfowl Research occurred primarily within 30 m of the focal loafing Station. Thanks are extended to Dr Roger M. spot and was not noted further away than 90 m. Evans. Dr H. A. Hochbaum, Mr Peter Ward, and Boundaries were well defined only where there Mr Rodger D. Titman for assistance in the collec­ were frequent interactions. Defence was primarily tion of data. Dr Evans and Dr W. Roy Siegfried of the water area and not the adjacent meadows. provided comments and assistance in writing the There was a vertical component to the territory. manuscript. The area used by pairs became significantly smaller (0-9 ha) after the onset of egg-laying. Terri­ tory size did not significantly change later in the season despite an increased concentration of pairs. Territories were remarkably stable and no pairs Summary lost territories as a result of hostility. However, stability may break down when the pair-bond The territorial behaviour of wild Shovelers Anas weakens with advance of incubation or when the clypeata was studied on a 1-9-km long roadside nest is destroyed. Certain areas were occupied by ditch at Delta, Manitoba, Canada. Most of the as many as three successive pairs. data used was derived from observations of seven­ Pairs spent virtually all their time on the terri­ teen marked males and three marked females. tory after egg-laying was well advanced. Females Breeding activity on the study area spanned 12 still used the territory after dissolution of the pair­ weeks and twelve diiferent territorial pairs were bond although their activities were restricted to observed. Breeding activity ceased late in the the area around the loafing spot.

References

Bartonek, J. C. & Dane, C. W. 1964. Numbered nasal discs for waterfowl. J. Wildl. Mgmt, 28:688-692. Dzubin, A. 1955. Some evidences of home range in waterfowl. Trans. 20th N. Amer. Wildl. Conf.: 278-298. Errington, P. L. 1946. Predation and vertebrate populations. Quart. Rev. Biol. 21:144-177, 221-245. Evans, C. D. & Black, K. E. 1955. A four-year duck study in the prairie potholes of South Dakota. Special Scientific Report: Wildlife. U.S. Fish and Wildlife Service. Gates, J. 1962. Breeding biology of the Gadwall in Northern Utah. Wilson Bull. 12:102-108. Geyr von Schweppenburg, H. 1924. Zur secualathologie der Stockente. Jour, fur Ornith. 72:102-108. Hinde, R. 1956. The biological significance of territories of birds. Ibis, 98:340-369. Hinde, R. A. 1966. Behaviour A Synthesis of Ethology and Comparative Psychology. McGraw, Hill, Toronto. Hochbaum, H. A. 1944. The Canvasback on a Prairie Marsh. Amer. Wildl. Inst., Washington, D.C. Hori, J. 1963. Three-bird flights in the Mallard. Wildfowl Trust 14th Ann. Rep.: 124-132. Lebret, T. 1961. The pair formation in the annual cycle of the mallard, Anas platyrhynchos L. Ardea, 49:97-158. Lincoln, F. C. & Baldwin, S. P. 1929. Manual for bird banders. U.S. Dept. Agriculture, Miscellaneous Public. 58:116. McKinney, F. 1965. Spacing and chasing in breeding ducks. Wildfowl Trust 16th Ann. Rep.: 92-106. McKinney, F. 1967. Breeding behaviour of captive Shovelers. Wildfowl Trust 18th Ann. Rep.: 108-121. McKinney, F. 1970. Displays of four species of blue-winged ducks. The Living Bird: 29-64. Noble, G. K. 1939. The role of dominance in the social life of birds. Auk, 56:263-273. Poston, H. J. 1968. Home range and breeding biology of the Shoveler. Unpublished M.Sc. thesis. Utah State Univ. Poston, H. J. 1969. Relationship between the Shoveler and its breeding habitat at Strathmore, Alberta. Saskatoon Wetlands Seminar. Can. Wildl. Serv. Rep. Series, 6:132-137. Siegfried, W. R. 1965. The Cape Shoveler Anas smithii (Hartert) in southern Africa. Ostrich, 36:155-198. Siegfried, W. R. 1968. The Black Duck in the south-western Cape. Ostrich, 39:61-75. Sowls, L. K. 1955. Prairie Ducks. Wildlife Management Institute, Washington, D.C. Tinbergen, N. 1939. Field observations of East Greenland Birds. II. The behaviour of the Snow Bunting (Plectrophenax nivalis subnivalis (Brehm)) in spring. Trans. Linn. Soc. N.Y. 5:1-94. Tinbergen, N. 1957. The functions of territory. Bird Study, 4 : 14-27. Ward, P. 1969. Tenth Seminar on the Breeding Biology of Waterfowl. Delta Waterfowl Research Station Seminar Report 10.

Norman Seymour, P.O. Box 6, MacDonald College, Quebec. HO A ICO, Canada.