Lek behavior of the Plovercrest (Stephanoxis lalandi, trochilidae).
|Abstract:||I examined the lek structure and behavior of male Plovercrests (Stephanoxis lalandi) at a lek in southern Brazil. The lek included seven territorial males; the distance between neighboring lek territories was 14.8 [+ or -] 6.3 m. Territory size was 11.4 [+ or -] 4.4 [m.sup.2]. Territory size and distance between territories were among the lowest reported for Trochilinae hummingbirds. Lek attendance by territory owners fluctuated throughout the day. Activity slowly diminished after an initial period of activity after arrival at sunrise, but increased again between 0900 and 1500 hrs. All males left their territories by 1830 hrs. Males sang at a similar rate (74.8 [+ or -] 14.5 songs/min) throughout the lekking season, but not throughout the day. There was no relationship between lek attendance and singing rate, two parameters that potentially affect mating success in lekking birds. Considerable interspecific variation occurs among lekking trochilines, indicating that much remains to be investigated about lek behavior and structure in hummingbirds.|
Animal behavior (Research)
|Author:||Pizo, Marco Aurelio|
|Publication:||Name: The Wilson Journal of Ornithology Publisher: Wilson Ornithological Society Audience: Academic Format: Magazine/Journal Subject: Biological sciences Copyright: COPYRIGHT 2012 Wilson Ornithological Society ISSN: 1559-4491|
|Issue:||Date: March, 2012 Source Volume: 124 Source Issue: 1|
|Topic:||Event Code: 310 Science & research Canadian Subject Form: Animal behaviour|
|Geographic:||Geographic Scope: Brazil Geographic Code: 3BRAZ Brazil|
Lekking behavior has been described for at least 28 species of
hummingbirds (Pizo and Silva 2001), and studies to date have revealed
considerable interspecific variation in the structure and dynamics of
hummingbird leks (Hoglund and Alatalo 1995, Ramjohn et al. 2003). For
instance, the number of males at leks may vary from two for Rufous
Sabrewings (Campylopterus rufus) (Skutch 1967) to >100 for
Long-tailed Hermits (Phaethornis superciliosus) (Skutch 1964a). Lekking
males may be clustered, as with male Broad-tailed Hummingbirds
(Selasphorus platycercus) that remain ~7 m apart (Barash 1972), or form
loose aggregations, as with male Swallow-tailed Hummingbirds (Eupetomena
macroura) that are 24-120 m apart (Pizo and Silva 2001). Activities at
leks may continue throughout the day (Phaethornis spp.; Ramjohn et al.
2003) or be limited to a short period such as dawn for Swallow-tailed
Hummingbirds (Pizo and Silva 2001).
Variation may reflect both phylogenetic and ecological constraints. However, Bleiweiss (1998) noted the repeated evolution of lekking behavior among hummingbirds, suggesting that behavior at leks is not limited by historical or phylogenetic constraints. Thus, to understand the relative roles of historical and ecological drivers in evolution of hummingbird leks, it is essential to expand our data base to include not only species representing different clades of the hummingbird phylogeny, but also to achieve a wider geographical sampling that encompasses contrasting ecological conditions.
My objective was to examine the lek structure and lek behavior of Plovercrests (Stephanoxis lalandi) in a subtropical area in southern Brazil. Stephanoxis is a monotypic genus of small hummingbirds (2.2-3.4 g, 8.5-9.0 cm), that occur in forests and semi-open areas from sea level to >2,000 m asl, ranging from eastern Paraguay to northeastern Argentina (Misiones), and southern and southeastern Brazil (Schucbmann 1999). Males of the race S. l. loddigesii that I studied have long iridescent blue crests with a conspicuous black patch on the underparts, whereas females are iridescent green with gray below and with feathers of the head only slightly elongated. Hummingbirds in the genus Stephanoxis are known to display at leks (Sick 1997, Sigrist 2006), but details of their lekking behavior are unreported. Phylogenetically, the genus Stephanoxis is placed within the Emerald clade (sensu McGuire et al. 2007), which includes genera that exhibit lekking behavior (e.g., Amazilia and Campylopterus) as well as apparently non-lekking species (e.g., Thalurania and Chlorostilbon). I also describe the song and aerial display of Plovercrests, their seasonal and daily patterns of activity at the lek, and the relationship between lek attendance (i.e., time spent in lek territories) and singing rate.
Study Area.--The lek studied was at the edge of an early secondary forest (sensu Clark 1996) extending along the margin of a 4.5-km road connecting Ivoti and Lindolfo Collor (29[degrees] 35' S, 51[degrees] 11' W; 130 m asl), two small towns in southern Brazil. The lek was in the transition area between the forest and an old field, where small trees and shrubs (<10 cm diameter at breast height, <8 m tall) gradually give way to patches of herbaceous vegetation averaging ~1 m in height. Common trees included Zanthoxylum sp. (Rutaceae) and Casearia sylvestris (Flacourtiaceae) interspersed with a few exotic Acacia mearnsii (Mimosaceae). The area was surrounded by extensive patches of secondary forest and small farm (usually < 10 ha) rural properties. Meteorological data collected at Sao Leopoldo, ~20 km from the study area, show that rain is well distributed throughout the year, totaling ~1,500 mm. The average monthly temperature is 19.8[degrees]C (range = 13.8-25[degrees]C).
Lek Structure and Male Behavior.--I conducted an initial survey to locate all territories occupied by singing males, and then observed each and all males (n = 7) on the largest lek during 15-min periods over 20 days from August to December 2006 totaling 22.75 hrs of observations (3.25 hrs/ male). Observations were randomly rotated among males so each was observed at least once during each hour of the day from 0600 to 1800 hrs. I recorded during each 15-min observation period: (1) the amount of time males spent in their lek territories, which for Plovercrests corresponds to singing activity as males were constantly singing when in their territories; (2) the number of songs uttered during a 1-min period recorded once at the middle of each observation period; and (3) the number of perches used for singing. I also noted all visits by conspecifics to lek territories but, due to the short duration of visits and the rapid movements of interacting birds, I was unable to ascertain the gender of every visiting bird. The heights of the perches used for singing were measured after each observation. Songs produced by lekking males were recorded with a Sony TCM 5000 recorder and a Sennheiser ME66 microphone. Sonograms were obtained using Raven Version 1.3 (Charif et al. 2007).
I measured the area of each territoryat the end of the study by considering them rectangular and taking the outermost singing perches as boundaries. This method may have overestimated the area of the territories, but I suspect this was not the case because boundaries of each territory were not delimited by perches used for singing and were extended to where visiting birds were chased. Thus, I am confident the method used provided estimates of territory sizes that did not greatly depart from real values. The distances between neighboring territories were taken from the approximate center of each territory. I continued to visit the lek area twice a month after the birds left the lek in December 2006 to look for singing males that could indicate resumption of lekking activity.
Males were not marked and I could not be certain that territory owners did not change during the study. However, based on consistent use of particular perches used for singing, the individually recognizable songs of some males, and the short duration of the study, I do not believe that such changes occurred. Thus, for analysis, I assumed the same individuals held their territories and were observed throughout the study.
Statistical Analyses.--One-way ANOVA was used to examine possible monthly and among-male differences in singing rates. Sample sizes were too small for some hours of the day when birds were generally absent from the lek, and daily variation in singing rate was not examined. Lek attendance data (defined as the proportion of the 15-min observation periods spent by males inside their lekking territories) were not normally distributed, and I used Kruskal-Wallis tests to evaluate daily and among-male variation in lek attendance. I checked for the homogeneity of variances of ranked data using the Brown-Forsythe test (Brown and Forsythe 1974) before performing Kruskal-Wallis tests, following the recommendations of Ruxton and Beauchamp (2008), which revealed homoscedasticity of variances. Pearson correlation tests were used to investigate the relationship between singing rate and lek attendance. all analyses were conducted with Statistica 6.1 (StatSoft 1999) with the level of significance of 0.05. Values are presented as means [+ or -] SD.
The largest lek consisted of seven male Plovercrests in an area ~70 X 30 m. Two other groups were also observed along the road, one 80 m (3 males) and the other 2 km (2 males) from the main lek, respectively. In addition, over a3-week period (23 Sep to 14 Oct 2006), I observed a solitary male singing 200 m from the main lek. Males were present at the leks (including those with 2 and 3 males) from August through mid-December 2006 with activity at the leks decreasing during December (Fig. 1A). The leks were inactive from December until the next July. However, at least six of the seven studied males returned to the main lek in August 2007; because they were unmarked, it is unknown whether all were among the original seven studied.
[FIGURE 1 OMITTED]
The mean area encompassed by lek territories was 11.4 [+ or -] 4.4 [m.sup.2] (n = 7, range = 7.0-16.0 [m.sup.2]). The mean distance between the center of territories was 14.8 [+ or -] 6.3 m (n = 7, range = 9.0-25.0 m). Males used from two to five perches to sing (3.4 [+ or -] 1.0 perches, n = 7) within their territories, usually slender horizontal branches 2.0 [+ or -] 0.8 m (n = 28, range = 0.8-3.5 m) above ground. I did not observe males feeding either inside their territories or at the lek area.
Territory owners received up to four visits of conspecifics per observation period of 15 min (0.5 [+ or -] 0.8 visits/observation period). Visits were slightly more frequent in early morning (0600-0700 hrs), but occurred throughout the day. Visitation rate varied only slightly through the breeding season. Upon arrival of a visiting conspecific in a territory, the resident male either immediately chased the intruding bird or, less often, the resident male and intruder engaged in a stereotyped aerial display. Immediate chases occurred when the visiting bird was either an adult male or birds in a female-like plumage (i.e., females or young males) as far as the brief encounters and rapid movements of interacting birds permitted me to identify, whereas the aerial display was reserved exclusively for adult males. The territory owner remained perched during aerial displays while watching the visiting bird perform a series of rapid, short (~10 cm) lateral flights just in front and slightly above it. Visiting birds kept their crests conspicuously erected while displaying. The territory owner, after a few seconds of displaying, either chased the visiting bird or the visiting bird flew away.
Males were frequently absent from their lek territories, and lek attendance by territory owners fluctuated throughout the day (H = 35.3, df = 12, P < 0.001; Fig. 2A). Males arrived at the lek area approximately at sunrise. Activity slowly diminished after an initial period of activity after arrival, but increased again around 0900 and 1500 hrs. all males left their territories by 1830 hrs (Fig. 2A).
The song given by lekking males was a complex, modulated vocalization uttered at a mean rate of 74.8 [+ or -] 14.5 songs/min (range = 46-101 songs/min, n = 39; Fig. 3). Males sang at a similar rate throughout the lekking season ([F.sub.4.34] = 0.4, P = 0.84; Fig. 1B), but not throughout the day (Fig. 2B). Singing rates at times increased briefly when males returned to their territories after a chase or when a conspecific passed nearby.
Overall, males were present on their territories during 35.8% of the observation periods with no differences among males (H = 4.9, df = 6, P = 0.56; Fig. 4A). I did find a difference among males in singing rates ([F.sub.6,32] = 5.8, P < 0.001; Fig. 4B), but singing rate was not correlated with lek attendance (r = 0.34, n = 7, P = 0.46).
The Plovercrest lek studied was similar to those of other lekking hummingbirds. For instance, hummingbirds often establish leks in edge habitats (Skutch 1958, Atwood et al. 1991) as did Plovercrests. Even species typical of dense forests, such as hermits, may establish leks in areas of secondary vegetation along trails and river margins or in forest gaps (Stiles and Wolf 1979; Ramjohn et al. 2003; M. A. Pizo, pers. obs.). Apparent preference for edge habitats may be the result of observer bias because these habitats are more accessible and more easily surveyed. I cannot totally eliminate the possibility of detection bias for Plovercrests, but efforts to locate singing males away from the road margin were unsuccessful. The preference for edge habitats by hermits has been hypothesized to stem from three non-exclusive reasons: (1) the high light levels of edge areas stimulate the growth of a dense understory where males establish singing perches; (2) the nearby occurrence of plants exploited by hummingbirds, which facilitate feeding by territorial males; and (3) open areas provide a convenient flight path for territorial males and visitors (Snow 1974, Stiles and Wolf 1979). I cannot discard any of the three reasons as influencing the settlement of Plovercrest leks. For instance, although the availability of a dense understory is likely more important for hermits, whose perches used for singing are usually lower (<2 m) than those used by trochilines (data in Table 1 vs. data summarized by Ramjohn et al. 2003), the height of the perches used for singing by Plovercrest is among the lowest reported for trochilines (Table 1). An additional reason for the putative preference for edge habitats, pertaining to trochilines, could be the importance of an adequate light level for the proper exhibition of particular patches in the plumage of displaying birds, as demonstrated for other lekking birds (Endler 1996). Trochilines, contrasting with the usually drab colors of hermits, have iridescent patches in the plumage whose full brightness depends on the correct light level. One such iridescent patch in Plovercrests, the male crest, is conspicuously shown in lekking displays.
[FIGURE 2 OMITTED]
The number of male Plovercrests at leks in my study (2-7) was within the range reported for other Trochilinae hummingbirds, which varies from two to 20 (Table 1). Territory size and distance between neighboring territories, however, were among the lowest values reported for trochilines (Table 1). Lek size in hummingbirds is likely influenced by population density, being negatively correlated with distance between neighboring territories (Snow 1973). Territory size may also be influenced by vegetation structure. Stiles and Wolf (1979) noted the smallest territories of Long-tailed Hermits in Costa Rica were in very dense thickets, while the largest territories were in open forest understory. The density of woody vegetation at the main Plovercrest lek was intermediate between a dense forest understory and an open field. Provided the observation by Stiles and Wolf (1979) can be generalized, Plovercrest leks in forest interior should have territories closer to each other than reported in my study.
Seasonal and daily activities at the Plovercrest lek in my study resembled those of other hummingbirds. Activity at hummingbird leks is either limited to the breeding season (Snow 1968, 1974), with the exception of Swallow-tailed Hummingbirds that are found at leks throughout the year (Pizo and Silva 2001), or is greatly reduced during the non-breeding season (Stiles and Wolf 1979). Lek activities for Plovercrests also coincide with the breeding period (Schuchmann 1999, Belton 2003).
The daily activity pattern of Plovercrests was similar to that described for White-bellied Emeralds (Amazilia candida; Atwood et al. 1991), and Long-tailed Hermits (Stiles and Wolf 1979), where males left the lek after a period of high singing rate in the early morning. Singing rates again increased after this interval, but then gradually diminished during the hottest hours of the day. The daily activity pattern at hummingbird leks as hypothesized by Stiles and Wolf (1979) likely reflects the need of displaying males to leave the lek area for foraging.
[FIGURE 3 OMITTED]
The aerial display of Plovercrests, in which a displaying bird hovers in front and slightly above a perched bird, is similar to the shuttle displays of North American hummingbirds (e.g., Anna's Hummingbird, Calypte anna; Stiles 1982). The aerial display of Plovercrests appears to be similar to those of lekking hummingbirds in the subfamilies Trochilinae (e.g., Swallow-tailed Hummingbirds, Pizo and Silva 2001) and Phaethornithinae (e.g., Long-tailed Hermits; Stiles and Wolf 1979), as well as those of some non-lekking species (e.g., Violet-capped Woodnymph [Thalurania glaucopis]; M. A. Pizo, pers. obs.). This suggests the aerial display described is deeply rooted in hummingbird phylogeny, and not restricted to lekking activities. Interspecific differences in these displays do exist. Hermits, for instance, often display their gape and throat patterns (Stiles and Wolf 1979), which apparently does not happen in Plovercrests. However, to properly evaluate these aerial displays and compare those of different species, recording the displays with video cameras for more detailed analysis will be necessary.
I found no relationship between lek attendance by male Plovercrests and singing rate in contrast to White-bellied Emeralds (Atwood et al. 1991). These authors interpreted singing rates as reflecting dominance hierarchies among lekking males that might affect mating success. They noted, however, the relationship between lek attendance and singing rate was detected when the three leks studied were pooled for analysis, but became less clear when each lek was analyzed separately. Thus, variation existed among leks of a single species, and certainly exists in an interspecific comparison. No relationship between lek attendance and singing rate was detected for Plovercrests, but singing rates differed among males. Relating differences to possible variation in mating success represents a challenge for researchers because copulations are seldom witnessed even for the best studied lekking hummingbirds (Stiles and Wolf 1979). A better understanding of the relationship between lek behavior and mating success will require a combination of field effort to locate hummingbird nests near leks, and laboratory analysis to ascertain the paternity of nestlings.
[FIGURE 4 OMITTED]
I thank Luiz Pedreira Gonzaga who prepared the sonogram, and K. L. Schuchmann, Johan Ingels, and an anonymous reviewer for critical comments on the manuscript. The author was supported by a research grant from the Brazilian Research Council (CNPq # 303559/2008-0).
Received 11 March 2011. Accepted 30 August 2011.
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MARCO AURELIO PIZO (1)
(1) UNESP-Universidad Estadual Paulista, Departamento de Zoologia, 13506-900 Rio Claro, SP, Brazil; e-mail: email@example.com
TABLE 1. Lek characteristics of Trochilinae hummingbirds. Ranges are presented whenever data for more than one individual territory and/or more than one lek were available. Species are in alphabetical order. Territorial Area of Distance between Species males/lek territories territories (m) ([m.sup.2]) Amazilia amabilis 5 15-30 A. candida 3-7 <450 14-32 A. tzacatl 2-4 15-22 Campylopterus up to 15 curvipennis C. ensipennis 2-4 C. excellens 2-3 C. hemileucurus 4 16 C. largipennis 2-4 C. rufus 2 Eupetomena macroura 15 133-266 24-120 Hylocharis eliciae 3 <30 Klais guimeti 4 15 Phaeochroa cuvierii 4 38 Selasphorus 3 7 platycercus Stephanoxis lalandi 2-7 9-25 9-25 Topaza pella 2-20 Perch Species height (m) Source (a) Amazilia amabilis 2.4-6 6 A. candida 3-15 9 A. tzacatl 2-6 7 Campylopterus 14 curvipennis C. ensipennis 2-10 11, 12 C. excellens 10 C. hemileucurus 4 C. largipennis 8 C. rufus 3-3.6 4 Eupetomena macroura 0.3-4.2 13 Hylocharis eliciae 5-13 6 Klais guimeti 6-18 2 Phaeochroa cuvierii 6-12 3 Selasphorus 5 platycercus Stephanoxis lalandi 0.8-3.5 This study Topaza pella 10.5 1 (a) Sources: I. Davis (1958): 2 Skutch (1958); 3. Skutch (19646): 4. Skutch (1967); 5. Barash ( 1972); 6. Skutch (1972); 7. Skutch (1981); 8. Hilty and Brown (1986): 9. Atwood et al. (1991); 10. Winker et al. (1992): 11. Hayes et al.( 1997): 12. Hayes et al. (2000); 13. Pizo and Silva (2001): 14. Hayes (2002).
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