What do foraging hummingbirds maximize?

Summary Hainsworth and Wolf (1976) reported that under certain conditions hummingbirds made food choices which did not maximize their net rate of energy intake while foraging. They concluded that the birds were not foraging optimally. We show here that their birds probably maximized a different utility function, the net energy per unit volume consumed (NEVC), which appears to be an optimal choice on a time scale longer than that of a foraging bout. Our own experiments with Archilochus colubris support the conclusion that hummingbirds make foraging decisions that maximize NEVC. A simulation model shows that, in nature, NEVC maximization would require fewer foraging trips and visits to fewer flowers per day to balance daily energy budgets. For territorial birds this can lead to smaller territory sizes and reduced costs of territorial defense. Plants that evolutionarily increase corolla length to enhance pollinator specificity need only increase nectar concentration slightly to maintain the same net energy per unit volume consumed (NEVC) by a given hummingbird pollinator.     

High foraging site fidelity and spatial segregation among individual great black‐backed gulls

Individual foraging site fidelity, whereby individuals repeatedly visit the same foraging areas, is widespread in nature, and likely benefits individuals through higher foraging efficiency and potentially, higher breeding success. It may arise as a consequence of habitat or resource specialisation, or alternatively, where resources are abundant or predictable, the partitioning of space might guarantee individuals exclusive foraging opportunities. We tracked seven adult great black‐backed gulls Larus marinus at a North Sea colony from early incubation to the end of the breeding season in 2016, providing a total of 1170 foraging trips over a mean ± SD tracking period of 67 ± 16 days. There was clear spatial segregation between individuals, with almost no overlap of their core areas (50% utilisation distribution) during incubation and chick‐rearing. Core areas were relatively small and there was high repeatability (R ± SE) in foraging parameters, including initial departure direction (0.73 ± 0.11), foraging range (0.41 ± 0.14) and cumulative distance travelled (0.19 ± 0.1) throughout the breeding season. Despite the low spatial overlap, there was little evidence of differential habitat use by individuals. The near‐exclusive individual foraging areas of this species, usually considered to be a generalist, indicate that where there is high resource availability throughout the breeding season and a small local population, individuals appear to adopt a territorial strategy which likely reduces intraspecific competition.     

BEHAVIORAL CONVERGENCE AND ADAPTIVE RADIATION: EFFECTS OF HABITAT USE ON TERRITORIAL BEHAVIOR IN ANOLIS LIZARDS

Most studies of adaptive radiations focus on morphological aspects of differentiation, yet behavior is also an important component of evolutionary diversification, often mediating the relationship between animal ecology and morphology. In species within radiations that are convergent in ecology and morphology, we then also expect convergence in behavior. Here, we examined 13 Anolis lizard species to determine whether territorial strategies have evolved convergently with morphology and habitat use. We evaluated two aspects of territoriality: behavioral defense of space via territorial displays, and territory overlap within and between sexes. Controlling for the phylogenetic relationships of the taxa in our study, we found that species similar in perch height and diameter convergently evolved patterns of territory overlap, whereas species similar in habitat visibility (the proportion of space that can be seen from a perch) convergently evolved display behavior. We also found that species with greater display time have more extensive male–male territory overlap. This study provides strong evidence for the role of habitat in the evolution of territoriality and suggests that the social structure of a species ultimately evolves in concert with habitat use and morphology.     

Singing strategies are linked to perch use on foraging territories in heart‐nosed bats

Acoustic communication allows animals to coordinate and optimize resource utilization in space. Cardioderma cor, the heart‐nosed bat, is one of the few species of bats known to sing during nighttime foraging. Previous research found that heart‐nosed bats react aggressively to song playback, supporting the territorial defense hypothesis of singing in this species. We further investigated the territorial defense hypothesis from an ecological standpoint, which predicts that singing should be associated with exclusive areas containing a resource, by tracking 14 individuals nightly during the dry seasons in Tanzania. We quantified the singing behavior of individuals at all perches used throughout the night. Using home range analysis tools, we quantified overall use, night ranges and singing ranges, as well as areas used in early and later time periods at night. Males sang back and forth from small (x¯ = 3.48 ± 2.71 ha), largely exclusive areas that overlapped with overall night ranges used for gleaning prey. Individuals varied in singing effort; however, all sang significantly more as night progressed. Subsequently, areas used earlier at night and overall use areas were both larger than singing areas. Individuals varied in singing strategies. Some males sang for long periods in particular trees and had smaller core areas, while others moved frequently among singing trees. The most prolific singers used more perches overall. Our results support the hypothesis that acoustic communication repertoires evolved in support of stable foraging territory advertisement and defense in some bats.     

Space‐use strategies of wintering Ovenbirds in Belize: causes and consequences

For long‐distance migrants, territoriality and prey biomass during the non‐breeding season have been linked to body condition that can carry over to affect spring migration and breeding events. For Ovenbirds (Seiurus aurocapilla), studies in Jamaica showed that body condition in mid‐season depended on leaf litter prey biomass and declined seasonally as conditions became drier, and that individuals with sedentary (territorial) and wandering space‐use strategies did not differ in age or body condition. During October and November 2010–2011, we radio‐tracked Ovenbirds in Belize to determine if space‐use patterns differed with age and sex, if space‐use strategy influenced foraging behavior or body condition, and if areas used by wanderers and territory owners differed in food abundance or habitat characteristics. Most Ovenbirds (41 of 51, 80.4%) possessed small (1‐ha) territories with largely non‐overlapping cores, but 22.5% (10 of 51) of birds were wanderers (～7‐ha home range). Early season space use was predicted by age class, with most wanderers (90%, 9 of 10) being first‐year birds and most territory owners (63%) being older birds. Sex ratios of wanderers and territory owners did not differ. We found that wanderers may have been at a disadvantage because they had significantly lower foraging rates and lower relative body masses than territorial birds, although baseline corticosterone levels did not differ. Habitat characteristics of areas used by wanderers and territory owners did not differ nor did biomass of ground‐surface arthropods, likely because ranges of most wanderers overlapped those of territory owners. Using stable hydrogen isotopes in feathers, we found that first‐year Ovenbirds that were wanderers tended to have a more northern natal origins than sedentary birds, though the difference was not significant. Longer migration distances could delay arrival and reduce competitive ability. Our results suggest that wandering may not be an alternative and equally successful strategy, at least early in the season, and instead young birds may be competitively excluded from territory ownership.     

Territorial defense, territory size, and population regulation

The carrying capacity of an environment is determined partly by how individuals compete over the available resources. To territorial animals, space is an important resource, leading to conflict over its use. We build a model where the carrying capacity for an organism in a given environment results from the evolution of territorial defense effort and the consequent space use. The same evolutionary process can yield two completely different modes of population regulation. Density dependence arises through expanding and shrinking territories if fecundity is low, breeding success increases gradually with territory size, and/or defense is cheap. By contrast, when fecundity is high, breeding success sharply saturates with territory size, and/or defense is costly, we predict fixed territory sizes and regulation by floaters. These "surplus" individuals form a buffer against population fluctuations. Yet floaters can also harm breeder performance, and by comparing population growth of a territorial population to a nonterritorial (and individually suboptimal) alternative, we can quantify the harmful effect of evolutionary conflict on population performance. Territoriality has often been found to increase population stability, but this may come at a cost of reduced equilibrium densities.     

Does intraspecific behavioural variation of pollinator species influence pollination? A quantitative study with hummingbirds and a Neotropical shrub

• Floral visitors differ in their efficacy as pollinators, and the impact of different pollinator species on pollen flow and plant reproduction has been frequently evaluated. In contrast, the impact of intraspecific behavioural changes on their efficacy as pollinators has seldom been quantified.
• We studied a self‐incompatible shrub Palicourea rigida (Rubiaceae) and its hummingbird pollinators, which adjust their behaviour according to floral resource availability. Fluorescence microscopy was used to access pollen tube growth and incompatibility reaction in pistils after a single visit of territorial or intruder hummingbirds in two populations. To characterise the plant populations and possible differences in resource availability between areas we used a three‐term quadrat variance method to detect clusters of floral resources.
• Within‐species variation in foraging behaviour, but not species identity, affected pollinator efficacy. Effectively, hummingbirds intruding into territories deposited more compatible pollen grains on P. rigida stigmas than territory holders in both study areas. Additionally, territory holders deposited more incompatible than compatible pollen grains.
• Our results imply that intraspecific foraging behaviour variation has consequences for pollination success. Quantifying such variation and addressing the implications of intraspecific variability contribute to a better understanding of the dynamics and consequences of plant–pollinator interactions.

     

Diet, foraging, and use of space in wild golden-headed lion tamarins

Lion tamarins (Callitrichidae: Leontopithecus) are small frugi-faunivores that defend large home ranges. We describe results from the first long-term investigation of wild golden-headed lion tamarins (L. chrysomelas; GHLTs). We present data about activity budgets, daily activity cycles, diet, daily path length, home range size, home range overlap, and territorial encounters for three groups of GHLTs that were studied for 1.5-2.5 years in Una Biological Reserve, Bahia State, Brazil, an area characterized by aseasonal rainfall. We compare our results to those from other studies of lion tamarins to identify factors that may influence foraging and ranging patterns in this genus. Ripe fruit, nectar, insects, and small vertebrates were the primary components of the GHLT diet, and gums were rarely eaten. Fruit comprised the majority of plant feeding bouts, and the GHLTs ate at least 79 different species of plants from 32 families. The most common foraging sites for animal prey were epiphytic bromeliads. The GHLTs defended large home ranges averaging 123 ha, but showed strong affinities for core areas, spending 50% of their time in approximately 11% of their home range. Encounters with neighboring groups averaged two encounters every 9 days, and they were always aggressive. Data about time budgets and daily activity cycles reveal that the GHLTs spent most of their time foraging for resources or traveling between foraging sites distributed throughout their home ranges. The GHLTs spent much less time consuming exudates compared to lion tamarins in more seasonal environments. Additionally, the GHLTs had much larger home ranges than golden lion tamarins (L. rosalia), and did not engage in territorial encounters as frequently as L. rosalia. GHLT ranging patterns appear to be strongly influenced by resource acquisition and, to a lesser extent, by resource defense.     

Do male roe deer clump together during the rut?

Movement s an d habitat use of 7 male and 7 female roe deerCapreolus capreolus (Linnaeus, 1758) were studied by radioteleme try from March 1999 to February 2001. Annual and bimonthly home ranges of males were small (ca 10 ha, 95% kernel), with large overlap among individuals throughout the year. Exclusive core areas (ca 0.4 ha, 25% kernel) were concentrated in the forest, a limited and sought-after resource in the study area. The difference in overlap between male exclusive core areas and female home ranges in the pre-rut and rut periods suggested that females made excursions to search for territorial males during the rut Our results support the mating strategy hypothesis of territorial behaviour Different space use patterns occurred between the sexes, with females apparently playing an active role in mate choice by visiting males at clumps of core areas in the forest.     

Interspecific Territoriality by a Rufous-Tailed Hummingbird (Amazilia tzacatl): Effects of Intruder Size and Resource Value1

I studied two aspects of interspecific territoriality in a Costa Rican nectarivorous bird, the rufous-tailed hummingbird (Amazilia tzacatl). First, I examined variation in the response of the territory holder to four species of intruding hummingbirds by quantifying the proportion of intruders chased from the territory. This measure of territory defense varied significantly among species of intruders and was negatively related to the intruding species’body mass, possibly due to potential costs associated with becoming involved in escalated contests with larger individuals. Second, I tested for an effect of resource manipulation on territory defense. I increased the resource value of the territory by injecting extant natural flowers with artificial sucrose solution. While the frequency of territorial intrusions did not change, the proportion of intruders chased by the territory holder increased. Apparently, nectar supplementation changed the territory holder's perception of resource value but had little impact on the intruders’perception.     

Territory quality determines social group composition in Ethiopian wolves Canis simensis

1. We contrast the value of four different models to predict variation in territory size as follows: resource density (the ideal free distribution), population density, group size and intruder pressure (relative resource-holding potential). In the framework of the resource dispersion hypothesis, we test the effect of resource abundance and spatial variation in resource distribution on the age/sex composition of social groups. 2. We explore these drivers of territory size and group size/composition in Ethiopian wolves Canis simensis in the Bale Mountains, Ethiopia, using fine-scale distribution maps of their major prey species based on satellite-derived vegetation maps. 3. The number of adult males is correlated with territory size, while prey density, wolf population density and intruder pressure are not associated with territory size. On average, each additional adult male increases territory size by 1.18 km(2). 4. Prey abundance increases with territory size (average biomass accumulation of 6.5 kg km(-2)), and larger territories provide greater per capita access to prime foraging habitat and prey. 5. The age/sex composition of wolf packs is more closely related to territory quality than territory size. Subordinate adult females are more likely to be present in territories with greater proportions of prime giant molerat Tachyoryctes macrocephalus habitat (i.e. >80% of Web Valley territories and >20% in Sanetti/Morebawa), and more yearlings (aged 12-23 months) occur in territories with greater overall prey biomass. 6. Wolf packs with restricted access to good foraging habitat tend to defend more exclusive territories, having a lower degree of overlap with neighbouring packs. 7. The greater per capita access to prey in large groups suggests a strong evolutionary advantage of collaborative territorial defence in this species, although the relative costs of territorial expansion vs. exclusion depend upon the spatial distribution of resources. We propose a model whereby territory size is determined by the number of adult males, with the presence of subordinate females and yearlings dependent on the quality of habitat, and the abundance and distribution of prey, incorporated within territory boundaries.     

Temporal partitioning of a floral resource by territorial hummingbirds

Most studies of territoriality in hummingbirds have focused on intraspecific competition for resources and the consequences for the spatial distribution of individuals within a habitat. As a result, we know little of the effects of interspecific competition for resources and less still of temporal resource partitioning. Here I describe the interactions of four species of tropical hummingbird which defended the same territory at different stages in the flowering period and at different times of the day. The pattern of territory defence was greatly influenced by the dominance hierarchy between species and the costs and benefits of territory ownership. I used a simple economic model to calculate the predicted territory size based on four potential strategies. Hummingbirds appeared to be defending territories of the smallest economical size, agreeing with two hypotheses: (1) that hummingbirds minimize the cost of territory ownership and (2) that hummingbirds maximize the time spent sitting. The model predicted accurately the observed pattern of territory acquisition; hummingbirds initiated defence as soon as the territory contained sufficient resources and were either displaced by a larger species or replaced by a smaller one as the value of the territory changed.     

Context-specific territorial behavior in urban birds: no evidence for involvement of testosterone or corticosterone

Testosterone produced by the gonads is a primary mediator of seasonal patterns of territoriality and may directly facilitate territorial behavior during an encounter with a potential intruder. Costs and benefits associated with territoriality can vary as a function of habitat, for example through differences in resource distribution between areas occupied by different individuals. We investigated behaviors in response to simulated territorial intrusions (hereafter territorial behaviors) in urban (Phoenix, Arizona) and nearby desert populations of two Sonoran Desert birds (Curve-billed Thrasher and Abert's Towhee). We also examined the degree to which these behaviors are mediated by testosterone (T) and the adrenal steroid, corticosterone (CORT), which can interact with T in territorial contexts. In both species, urban birds displayed more territorial behaviors than their desert conspecifics, but this difference was not associated with variation in either plasma total or in plasma free (i.e., unbound to binding globulins) T or CORT. In addition, neither plasma T nor plasma CORT changed as a function of duration of the simulated territorial intrusion. Urban Abert's Towhees displayed more territorial behaviors in areas where their population densities were high than in areas of low population densities. Urban Curve-billed Thrashers displayed more territorial behaviors in areas with a high proportion of desert-type vegetation, particularly in areas that differed in vegetation composition from nearby randomly sampled areas, than in areas with a high proportion of exotic or non-desert type vegetation. Associations between territorial behavior and habitat characteristics were not related to plasma T or CORT. Understanding the hormonal processes underlying these associations between behavior and habitat may provide insight into how free-ranging animals assess territorial quality and alter their defensive behavior accordingly.     

Foraging habitats and utilization distributions of Black-necked Cranes wintering at the Napahai Wetland, China

ABSTRACT.   One of the most endangered populations of Black-necked Cranes ( Grus nigricollis ), the central population, is declining due to habitat loss and degradation, but little is known about their space use patterns and habitat preferences. We examined the space use and habitat preferences of Black-necked Cranes during the winter of 2007–2008 at the Napahai wetland in northwest Yunnan, China, where approximately 300 Black-necked Cranes (>90% of the total central population) spent the winter. Euclidean distance analysis was employed to determine the habitat preferences of Black-necked Cranes, and a local nearest-neighbor, convex-hull construction method was used to examine space use. Our results indicate that Black-necked Cranes preferred shallow marsh and wet meadow habitats and avoided farmland and dry grassland. Core-use areas (50% isopleths) and total-use areas (100% isopleths) accounted for only 1.2% and 28.2% of the study area, respectively. We recommend that habitat protection efforts focus on shallow marsh and wet meadow habitats to maintain preferred foraging sites. Core-use areas, such as the primary foraging areas of Black-necked Cranes, should be designated as part of the core zone of the nature reserve. Monthly shifts in the core-use areas of the cranes also indicate that the reserve should be large enough to permit changes in space use. In addition to preserving habitat, government officials should also take measures to decrease human activity in areas used by foraging Black-necked Cranes.     

Territory Characteristics among Three Neighboring Chimpanzee Communities in the Taï National Park,Côte d'Ivoire

We studied territory characteristics among three neighboring chimpanzee communities in the Taï National Park, Côte d'Ivoire, and compared them with other chimpanzee populations. We characterized territories and ranging patterns by analyzing six variables:, (1) territory size, (2) overlap zone, (3) territory utilization, (4) core area, (5) territory shift, and (6) travel distance. Data collection covered a period of 10 mo, during which we simultaneously sampled the local positions of mostly large parties, including males in each community, in 30-min intervals. In Taï, chimpanzees used territories in a clumped way, with small central core areas being used preferentially over large peripheral areas. Although overlap zones between study communities mainly represented infrequently visited peripheral areas, overlap zones with all neighboring communities also included intensively used central areas. Territory utilization was not strongly seasonal, with no major shift of activity center or shift of areas used over consecutive months. However, we observed shorter daily travel distances in times of low food availability. Territory sizes of Taï chimpanzees tended to be larger than territories in other chimpanzee communities, presumably because high food availability allows for economical defense of territorial borders and time investment in territorial activities. Therefore we suggest, that use of territory in Taï chimpanzees is strongly influenced by intercommunity relations. To understand differences in territory characteristics between various populations, it is of major importance to consider not only the intracommunity but also the intercommunity context.     

Influence of normal daytime fat deposition on laboratory measurements of torpor use in territorial versus nonterritorial hummingbirds

Fat deposition and torpor use in hummingbirds exhibiting distinct foraging styles should vary. We predicted that dominant territorial hummingbirds will use torpor less than subordinate nonterritorial species because unrestricted access to energy by territory owners allows for fat storage. Entry into torpor was monitored using open-flow respirometry on hummingbirds allowed to accumulate fat normally during the day. Fat accumulation was measured by solvent fat extraction. Territorial blue-throated hummingbirds (Lampornis clemenciae) had the highest fat accumulation and used torpor only 17% of the time. Fat storage by L. clemenciae averaged 26% of lean dry mass (LDM) in 1995 and 18% in 1996, similar to that measured for other nonmigratory birds. Fat storage by magnificent hummingbirds (Eugenes fulgens; trapliner) and black-chinned hummingbirds (Archilochus alexandri; nectar robber) averaged 19% and 16% of LDM, respectively, and they used torpor frequently (64% and 92% of the time, respectively). All species initiated torpor if total body fat dropped below 10% of LDM, indicating the existence of a torpor threshold. The ability of L. clemenciae to store enough fat to support nighttime metabolism is likely an important benefit of territoriality. Likewise, frequent torpor use by subordinates suggests that natural restrictions to energy intake can impact their energy budget, necessitating energy conservation by use of torpor.     

Energetic cost of feeding territories in an Hawaiian honeycreeper

Summary By analysis of time budgets the daily energy expenditure in territorial individuals of a Hawaiian honeycreeper (Vestiaria coccinea, Fam. Drepanididae) were estimated during the nonbreeding season and compared to that of nonterritorial individuals. The mean rise in living costs was 2.3 kcal/24 h or 17% of the nonterritorial energy budget. The most costly territorial behavior was advertisement rather than chasing, and total territorial cost was seen to be little affected by the number of intruders or the size of the territory. These results are compared with data on feeding (nonbreeding) territories of other nectar-feeding birds. The suggestion is made that hummingbirds may be more likely to develop nonbreeding territorial behavior in any set of environmental circumstances than are honeycreepers because of relatively lower total cost of advertisement plus chasing.     

Territorial behavior of Western Sandpipers on their nonbreeding grounds: effect of sex and foraging interference

ABSTRACT Nonbreeding shorebirds often alternate social structure between anonymous flocks and territorial behavior in response to different environmental factors. To evaluate specific drivers for one species, we studied the spacing behavior of wintering Western Sandpipers (Calidris mauri) at Bahía Santa María, northwestern Mexico, using behavioral observations. The density, population structure, and territorial behavior of Western Sandpipers differed among three habitat types. Cattail marshes supported 110 birds per ha, 49% males, and no territorial birds. Mangrove flats supported 288 birds per ha, 58% males, and 5% territorial birds. Brackish flats supported 365 birds per ha, 76% males, and 7% territorial birds. Territories consisted of rectangular strips (5–9 m long, N= 77). Territory length was not related to either bird density or number of territorial birds by plot, but was positively related to nearest bird distance. Aggression rate was inversely related to territory length, suggesting that territory length is set by the costs of defense. Foraging rate was independent of territory length, and prey densities in territories did not differ from those in areas used by nonterritorial birds. Males were more likely to be territorial and had a higher aggression rate than females, suggesting that males, which forage more on surface prey, were more affected by foraging interference. Our results suggest that the territorial behavior of Western Sandpipers in our study was an opportunistic strategy to reduce foraging interference. The variation in spacing behavior we documented provides evidence that interference competition affects the social structure of Western Sandpipers during the nonbreeding season.     

Cost of territory establishment in hummingbirds

Summary Time spent in territorial defense was measured during territory establishment for non-breeding Black-chinned (Archilochus alexandri) and Anna's (Calypte anna) hummingbirds. Newly established territory holders spent more time chasing intruders than neighboring established owners, which served as controls. This higher investment in defense by the new owners was due to 1) a longer time spent per each chase and 2) in some cases, a higher frequency of chases at the onset of territory ownership.     

Energy regulation by traplining hummingbirds

1. A published model of constant diurnal energy accumulation by territorial hummingbirds does not accurately reflect the temporal distribution of feeding behaviour of traplining hummingbirds, Phaethornis longirostris (Long-Tailed Hermit Hummingbirds).
2. In an enclosure study, gross nectar intake by P . longirostris decreased through the day, mirroring nectar production rates in its natural food-flowers and mimicking its natural foraging patterns.
3. Using a simulation model, the energetic consequences of constant and decreasing net energy intake rates for traplining hummingbirds are compared.
4. Given natural patterns of nectar production, model birds with decreasing diurnal net intake rates met their energetic needs with fewer flowers than those with constant net intake, and spent less time foraging.
5. It is concluded that P . longirostris do not satisfy the physiological assumptions of the published model, and that in this way they are different from the territorial species on which the model has previously been tested.