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Nectar and flower production of Lobelia telekii inflorescences, and their influence on territorial behaviour of the scarlet-tufted malachite sunbird ( Nectarinia johnstoni )

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The alpine zone of Mount Kenya is a typical equatorial, high-altitude habitat with a harsh environment, large fluctuations in physical conditions and an impoverished flora and fauna. A common flowering plant isLobelia telekii, which has large
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  BiologicalJournal ofthe Linnean zyxwvuts ociety zyxwvuts 1996), 57: 89-105. With 8 figures zyxw Nectar and flower production of Lobelia telekii inflorescences, and their influence on territorial behaviour of the scarlet-tufted malachite sunbird (Nectarinia ohnstoni) MATTHEW zyxwv . EVANS Department zyxwvu f Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ Received 25 March 1994, acceptedfor Publication 13 March 995 The alpine zone of Mount Kenya is a typical equatorial, high-altitude habitat with a harsh environment, large fluctuations in physical conditions and an impoverished flora and fauna. A common flowering plant is Lobelia tekkii, which has large inflorescences with up to 2000 flowers. The long hanging bracts of this plant ameliorate the physical environment around the flowers, damping the fluctuations in temperature and relative humidity. The scarlet-tufted malachite sunbird (Nectarinia johnston ) is a highly active nectarivore that obtains most of its food from the nectar of L. telekii. Sunbirds are more likely to visit the younger, male flowers at the suex of the inflorescence, which are larger and contain twice as much sugar as the older, female flowers lower down the spike. Male flowers will gain from multiple visits by exporting more pollen, while female flowers probably need to be visited only a few times for successful fertilization. Male sunbirds were resident on their territories all year and vigorously defended them from conspecifics. All territories contained about four times the number of flowers visited by the territory occupants in a day. Males on territories with a large number of flowers suffered more intrusions than males on low quality territories and spent more time in flight. After an intrusion the resident male frequently fed near where the intrusion took place. Males that subsequently attracted mates defended about twice as many flowers as males that did not breed, although undefended inflorescences were present. Some males apparently defended territories suitable for a pair, others only for a single bird. zy   I996 The Linnean Society of London ADDITIONAL KEY WORDS:-territoriality zyxwv   sunbirds Lobelia co-adaptation Mount Kenya afro-alpine. CONTENTS Introduction ................... 90 Methods. ................... 92 Study site ................... 92 L. telekii inflorescences ............... 92 Scarlet-tufted malachite sunbird territoriality .......... 93 Present address: Department of Biological Molecular Sciences, University of Stirling, Stirling, FK9 4LA. 0024-4066/96/020089+ 17 18.0010 89 zyxw   996 The Linnean Society of London  90 M. R. EVANS Results zyxwvutsr .............. Production and turn-over of flowers zyxwvu n zyxwvu   zyxwvu elekii inflorescences . The role of the bracts ........... Pollination biology ........... Temtory size and quality .......... Territorial behaviour ........... Discussion .............. Strategies adopted by L telekii to maximize reproductive success Co-adaptation of the scarlet-tufted malachite sunbird and L. telekii Territorial behaviour of scarlet-tufted malachite sunbirds . . Acknowledgements ............ References .............. Standing crop of nectar .......... Adaptations of L telekii to the afro-alpine environment ... ..... 94 ..... 94 ..... 95 ..... 96 ..... 97 ..... 97 ..... 99 ..... 99 ..... 99 ..... z 01 ..... 102 ..... 102 ..... 104 ..... 104 INTRODUCTION The environment encountered in high altitude habitats is often harsh, and as a result the flora and fauna may be impoverished relative to lower elevations. The relative paucity of species in these areas, however, makes community organization simple and therefore creates ideal situations for the investigation of behaviour. The afro-alpine zone of Mount Kenya is a good example of such a simple environment. There is only one common species of nectarivore, the scarlet-tufted malachite sunbird (Nectarinia johnstonz’). There are no known nectarivorous insects (personal observation; Coe, 1967). Scarlet- tufted malachite sunbirds feed almost exclusively on the nectar of the ostrich plume lobelia (Lobelia telekii), but will occasionally visit the less specialized water-filled lobelia (L. keniensis)). This means that the standing crop available to the birds can be accurately assessed by measuring the nectar of L. telekii and that nearly all nectar losses are the result of feeding by the sunbirds. The inflorescences of L. telekii are large, cylindrical structures up to three metres high that contain up to 2000 flowers. Each flower on the inflorescence has a long, narrow, hairy bract which hangs over lower flowers. These bracts overlap producing a barrier between the environment and the flowers. The purple flowers contain a very viscous, highly concentrated (mean percentage sucrose 59.5 zyxwv   5.3%, zyxw = 36) nectar at relatively small volumes (4.59 .60 pl, n=43), similar to that observed in a high altitude Tropaeolum species in Costa Rica (Hainsworth Wolf, 1972a) which is used by the hummingbird Sehphorus jlummula. In L. telekii, each flower is a sequential hermaphrodite: the young flowers at the apex of the inflorescence are male, and the slightly older flowers below are female (Young, 1982) (Fig. 1). The plants are dependent on the sunbird for effective pollination. Self-pollinated inflorescences set less seed than inflorescences to which sunbirds were allowed access (Young, 1982). A plant only produces one inflorescence, which may grow for up to two years. Prior to the development of the inflorescence the young plant grows as a rosette of leaves for up to two years. To study territorial behaviour it is often necessary to measure the resources which can be obtained from the territory and the costs of defending those resources. This is usually difficult because competing species may depress available resources, and a consumer may feed on many different types of resource. Nectarivorous birds provide good examples in which the resources held by individuals may be easily quantified and manipulated (Wolf  SUNBIRD zyxwvut ERRITORIALITY zyxw ND zyx OBELL4 zyx 1 unopened flowera nectar producing male flowera nectar producing female flowers fertilized female flowera not producing nectar basal rosette Figure 1 Photograph of a typical zyxwvut   telekii inflorescence on Mount Kenya with outline to show limits of unopened male female and non-nectar producing fertilised flowers; bar represents 25 cm. Hainsworth, 1978), and this probably explains the large amount of work on foraging and territorial behaviour devoted to this group. The work presented here was conducted during a wider study of territorial behaviour of the scarlet-tufted malachite sunbird (Necturiniu johnstoni) on Mount Kenya (Evans  z   Hatchwell, 1992). The aims of this paper are: (a) to describe how nectar availability on L. telekii inflorescences is related to the requirements of flowers in different stages of the reproductive cycle, (b) to relate nectar availability to the foraging behaviour of the sunbirds, and (c) to examine the territorial behaviour of this species. Male scarlet-tufted malachite sunbirds defend areas (1700 m2 to 3300 m2 Evans Hatchwell, 1992) from conspecifics. They and their mates obtain nearly all their food from within the territory. Not all territorial males successfully attract mates during the breeding season; in 1989 57 of territorial males obtained a mate, and in 1990 87 did so (Evans, 1991). There is a large population of non-territorial birds (probably immature birds) which intrude on the territories, and territory owners also occasionally trespass on the territories of neighbours. Because of this, a large amount of time is spent by territorial males in repelling intrusions by other males (Evans Hatchwell, 1992). The territorial behaviour and aggressive displays of these birds are described in detail in Evans Hatchwell (1992). Both territory area and the standing crop of nectar on a territory should influence the territorial behaviour of resident birds. When territory area is  92 M. R. EVANS zyxwv arge it may take longer to remove intruders (Gibb, 1956; Gill z   Wolf,  1975). If an intruder feeds on a territory, the resources available to the resident will be depressed (Gibb, 1956; Davies Houston, 1981;  Ewald Orians, 1983). If intruder pressure is related to territory quality then intrusion frequencies should be greater on high quality territories (Carpenter, 1987). Gill and Wolf (1975) showed that golden-winged sunbird zy N. reichenowi) territories varied in area by a factor of 300 but the number of flowers defended varied only by a factor of five times. In this study the influence of territory size and standing crop of nectar on territorial defence and foraging behaviour are examined. METHODS Study site Data were collected at a study site in the Teleki Valley on the western side of Mount Kenya, from January to May 1989 and from January to February 1990. The study site covered both sides of the Teleki Valley at an altitude of 4000 m in the middle of the afro-alpine zone. This area is described in detail by Coe (1967). L. telekii inflorescences Prior to the 1989 sunbird breeding season (10 January) all inflorescences were mapped with reference to a 20 m x 20 m grid marked out over the study area. The position of each inflorescence was mapped by triangulation from the intersections of the grid. The height of every inflorescence was measured on the same day. To estimate the relationship between inflorescence height and the number of flowers of different sexes, five L. telekii inflorescences, covering the observed range of heights in the population over the study area, were measured between January and May and the number of flowers in each stage of the reproductive cycle was counted. On a different set of plants individual flowers were marked using pieces of coloured thread lightly tied around the bract below the flowers (number of plants=4, number of flowers per plant=8). Once every five days each of these flowers was inspected to determine its reproductive phase. This allowed the duration of each stage of the reproductive cycle to be estimated. The standing crop of nectar, the most relevant measure of food avail- ability, was determined in flowers of each sex. These data were taken as percentage sucrose on a weight to weight basis (Bolten et zy L, 1979) and converted to mg of sucrose equivalents. The standing crop of nectar and reproductive phase of flowers on different inflorescences was measured six times during the 1989 field season. A total of 82 flowers were used in this analysis (50 males and 32 females). Because the nectar of L. telekii flowers is extremely viscous (with a syrup-like consistency), it could not be sampled in the conventional way using micro-capillaries to draw the nectar out of each flower. Instead, flowers were removed from the plant and z   known volume (usually 5 pl) of distilled water was added into the corolla via a  SUNBIRD zyxwvut ERRITORIALITY AND zyxw OBEUA 93 micro-capillary; this was left for ten minutes and then withdrawn using a glass micro-capillary. The refractive index of the solution was measured using a hand-held sugar refractometer adjusted for small volumes and the volume of the solution was recorded. A second sample of distilled water was added to the flower in the same manner and the procedure repeated until the refractive index of the solution reached zero, indicating that all the nectar had been removed from the corolla. From the volume and concentration of each solution extracted from the flower and the volume of water added to the corolla, the volume of nectar and concentration of sugar in the nectar could be calculated. Since relative humidity and temperature in the vicinity of the flowers influences nectar concentrations (Corbet et aL, 1979), these measurements were taken to examine the influence the bracts had on ameliorating the highly variable ambient conditions. The intra-inflorescence temperature and ambient temperature were recorded on a different inflorescence on six days during the breeding season using a digital thermometer fitted with a thermocouple (Unwin, 1980). The intra-inflorescence temperature was recorded in the air space between the bracts and the flowers. Ambient temperature was recorded at the same level as the intra-inflorescence temperature just outside the bracts. Ambient and intra-inflorescence relative humidity were recorded in parallel with the temperature readings, using a modified method after Unwin (1980). Instead of supporting droplets of potassium acetate in wire loops, drops were placed on a coverslip and allowed to equilibrate with the air for 1 h. The refractive index of the potassium acetate solution was then measured using a hand refractometer and converted to relative humidity using the conversion given in Unwin (1980). Intra-inflorescence relative humidity was measured by balancing the coverslip on a bract in the space between the bracts and the flowers. Ambient relative humidity was measured at the same height above the ground zyxwv s the intra-inflorescence measurement. Scarlet-tuJied malachite sunbird territoriality In both years birds were individually marked with a maximum of two colour rings. The territories of 20 marked males in 1989 and 55 marked males in 1990 were mapped and the location of every L. telekii inflorescence used by each male was recorded. As the territories were contiguous, mapping was continued until the male which defended every inflorescence was known. A territory was defined as the polygon enclosing all the inflorescences and other plants known to be used by a particular sunbird. Territory areas were calculated by weighing cut-outs of the mapped territories and comparing the weights with cut-outs of known areas mapped to the same scale. The progress of all breeding attempts on each territory was followed. In 1989 10-minute time budgets were taken from both male and female sunbirds during the hours of daylight. The sampling sequence followed each day was derived from random number tables (over the season a mean of 6.8 time budgets were conducted per bird, minimum 3, maximum 11). In 1990 three 10-minute time budgets were taken on every male. After location, the bird was followed for 5 min before the time budget was started. This

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