Floral resource availability and hummingbird territorial behaviour on a Neotropical savanna shrub

Abstract

The influence of floral resource availability on behaviour and dominance hierarchy of hummingbirds has seldom been investigated in open tropical environments. We evaluated the behavioural changes of hummingbirds associated with Palicourea rigida, a shrub common in the Cerrado, the open savanna areas in Central Brazil. We observed the foraging behaviour as a function of resource availability and experimentally manipulated floral display and nectar in order to define resource thresholds associated with territorial behaviour and territory intruding behaviour. Territorial behaviour was observed only in patches with high floral abundance and was restricted to some hummingbird species. The large Eupetomena macroura seems to be the dominant species in the community, excluding other hummingbirds and holding the richest patches. The experimental reduction in the floral abundance and nectar led to the abandonment of territory by these hummingbirds, which reinforces the idea that a certain threshold is necessary to maintain territorial defence. Higher floral display, on the other hand, seems to lead to higher frequency of intrusions and higher behavioural complexity of territory defenders, possibly meaning greater energy expenditure. The flower number and nectar manipulation affected visitation rates of territorial hummingbirds, but the frequency of intruders was affected only by the former manipulation. This indicates that territorial intruder use visual cues (floral abundance) as indicators of resource availability in order to estimate cost-benefit of territory invasion. Although territorial behaviour could limit pollen flow in patches with larger floral displays, this may be compensated by the territory invaders, which bring pollen from other patches. Zusammenfassung Der Einfluss von Ressourcenverfügbarkeit von Blüten auf das Verhalten und die Dominanzhierarchie von Kolibris in offenen, tropischen Landschaften ist bisher nur selten untersucht worden. Wir erfassten Verhaltensveränderungen von Kolibris in Assoziation mit Palicourea rigida, einem häufiger Strauch in der Cerrado, der offenen Baumsavanne in Zentralbrasilien. Wir untersuchten das Foragierverhalten als eine Funktion der Ressourcenverfügbarkeit. Dazu manipulierten wir Blüten-und Nektarverfügbarkeit experimentell um Schwellenwerte von Ressourcenverfügbarkeit, assoziiert mit Territorialverhalten, zu schätzen. Territorialverhalten wurde nur an Stellen mit hoher Blütenabundanz beobachtet, und war beschränkt auf nur einige Kolibriarten. Der große Eupetomena macroura scheint die dominante Art in der Gemeinschaft zu sein: diese Art schloss andere Kolibriarten aus und besetzte die reichsten Stellen. Die experimentelle Verringerung von Blüten-und Nektarverfügbarkeit führte zum Verlassen von Territorien durch diese Kolibris, welches die Idee eines Schwellenwertes, für die Entstehung von Territorialverhalten unterstützt. Vermehrte Blü-tenverfügbarkeit jedoch führte scheinbar zu einer höheren Frequenz von Intrusions, und zu höherer Komplexität des Verhaltens des Verteidiger...

Pollination and breeding system of Canna paniculata(Cannaceae) in a montane Atlantic Rainforest: asymmetric dependence on a hermit hummingbird

“…This is further supported if one considers that for C. indica pollinated by H. furcifer, a presumably territorial hummingbird, fruit set in control flowers was only 20% in comparison to 86% in hand crossed flowers (Glinos & Cocucci 2011). These results illustrate the link between distinct hummingbird behaviors (e.g., territorialism) and pollination success (Justino et al 2012). At the community level, in the studied montane Atlantic Rainforest site, P. eurynome is a "core" hummingbird pollinator, interacting with more plant species than any other hummingbird species, and being the sole pollinator of many long-tubed flowers; at least 24 other plant species, 15 of which have overlapping flowering with C. paniculata .…”

When hummingbirds are the thieves: visitation effect on the reproduction of Neotropical snowbell Styrax ferrugineus Nees & Mart (Styracaceae)

“…Justino et al 2012). In studies with the genus Styrax, bees and other insects are always mentioned as visitors and pollinators, but visits by birds have not been recorded (Kato & Hiura 1999;Huang et al 2003).…”

“…Hummingbirds visited fl owers more frequently early in the morning when the standing crop was higher, while most insect groups visited or tended to visit fl owers more frequently at noon. While the visits of hummingbirds are frequently associated to nectar availability (Brown et al 1981;Justino et al 2012), insect visits are more infl uenced by the temperature than nectar availability (Brown et al 1981). During the cold dry season in the Cerrado the temperature can be considerably low early in the morning and before dusk, which probably hindered most insect visitors.…”

“…The agonistic territorial defense was restricted to other hummingbirds and large, high-energy-demanding bees. Since flower choice and feeding behavior of hummingbirds are strongly related to nectar availability (Justino et al 2012), territorial behavior was observed mostly early in the morning, when there was a higher nectar standing crop. This contrasts with truly ornithophilous plants, such as Palicourea rigida Kunth in cerrado, which receive frequent visits from hummingbirds and are defended all day long (Justino et al 2012).…”

Feeding behavior by hummingbirds (Aves: Trochilidae) in artificial food patches in an Atlantic Forest remnant in southeastern Brazil

“…Since the energetic cost of defending a territory can be up to three times higher than the cost of non-aggressively foraging (Gill and Wolf 1975), it is expected that individuals will engage in resource defense only when the fitness benefits of territoriality outweigh its costs (Brown 1964). Territorial individuals commonly have access to more food than subordinate ones (Justino 2009, Rios et al 2010, and the intensity of the defense should increase with the quality of the defended resource (Justino et al 2012). Hummingbirds, for example, defend clumped flowers rich in nectar more aggressively than scattered flowers (Temeles et al 2005).…”