Of hummingbirds and helicopters: Hovering costs, competitive ability, and foraging strategies

Wing morphology and flight kinematics profoundly influence foraging costs and the overall behavioral ecology of hummingbirds. By analogy with helicopters, previous energetic studies have applied the momentum theory of aircraft propellers to estimate hovering costs from wing disc loading (WDL), a parameter incorporating wingspan (or length) and body mass. Variation in WDL has been used to elucidate differences either among hummingbird species in nectar-foraging strategies (e.g., territoriality, traplining) and dominance relations or among gender-age categories within species. We first demonstrate that WDL, as typically calculated, is an unreliable predictor of hovering (induced power) costs; predictive power is increased when calculations use wing length instead of wingspan and when actual wing stroke amplitudes are incorporated. We next evaluate the hypotheses that foraging strategy and competitive ability are functions of WDL, using our data in combination with those of published sources. Variation in hummingbird behavior cannot be easily classified using WDL and instead is correlated with a diversity of morphological and physiological traits. Evaluating selection pressures on hummingbird wings will require moving beyond wing and body mass measurements to include the assessment of the aerodynamic forces, power requirements, and power reserves of hovering, forward flight, and maneuvering. However, the WDLhelicopter dynamics model has been instrumental in calling attention to the importance of comparative wing morphology and related aerodynamics for understanding the behavioral ecology of hummingbirds

Foraging ecology of common dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand : a thesis presented in fulfilment of the requirements for the degree of Master of Science (Zoology), Massey University, Albany, New Zealand

This study investigated the foraging ecology of common dolphins (Delphinus sp.) in the Hauraki Gulf Marine Park, off the east coast of Auckland. New Zealand. Like most species of small cetacea in the Southern Hemisphere, its foraging habits are poorly described. A total of 59 focal group follows of common dolphins were conducted between January and April 2006. Observations were conducted at the surface, recording the predominant behavioural state of the group, foraging phase, foraging strategy, group dispersion, group formation, swimming style, group heading, calf presence and associated species. All occurrences of fission-fusion events and surface behaviours were recorded. This study tested the hypothesis that foraging behaviour of common dolphins would be influenced by environmental and physical parameters, group size, calf presence and associations with other species. In the Hauraki Gulf, foraging behaviour was recorded during all common dolphin follows, with 14% ± 1.7 (mean ± s.e.) of time spent feeding. Larger groups of dolphins spent more time foraging than smaller groups. Herding accounted for a large part of the foraging behaviour of common dolphins (mean ± s.e. = 28% ± 2.3. n = 54). Larger groups were found to spend significantly more time herding than smaller groups. Herding was generally directed towards the nearest landmass. Common dolphins use a variety of foraging strategies, both individual and group coordinated strategies. High-speed pursuits (n = 29) and kerplunkmg (n= 15) were the only individual foraging strategies recorded. Coordinated feeding strategies employed were synchronous diving (n = 50), Ime-abreast (n = 28), carouselling (n = 26) and wall-formation (n = 4). Synchronous diving and carouselling were the most enduring strategies, accounting for a significant proportion of foraging behaviour (mean ± s.e. - 32% ± 0.05 and 24% ± 0.08 of instantaneous samples, respectively). Foraging strategies were typified by vanous group formations, dispersion between group members, swimming styles and breathing intervals. Foraging strategies were also observed to have different roles in dolphin foraging. Line-abreast and wall- formation were associated with herding. However, high-speed pursuit, kerplunking and carouselling were strategies synonymous with feeding. Foraging strategies were shown to be dynamic, with dolphin groups changing strategies within a foraging bout (mean ± s.e. = 3 ± 0.4). Larger groups spent more time engaged in coordinated foraging strategies than smaller groups. Noisy surface behaviours and fission-fusion events were frequently seen in synchrony with foraging behaviour. Calves present in a foraging group, typically assumed a central position in the group during herding, but remained on the periphery during feeding. When feeding, common dolphins frequently were associated with Australasian gannets (Morus senator), shearwaters (Puffinus spp.) and Bryde's whales (Balaenoptera brydei) Observations on the predatory behaviour of each species suggested a temporary close association between birds, whales and dolphins. This study showed an association of Australasian gannet flocks (n =46) and Bryde's whales (n = 27) with common dolphins, and described the nature of the joint aggregations of mixed-species feeding in the Hauraki Gulf. The behaviour of gannots and whales strongly coincided with that of the foraging dolphin group. Whales were recorded tracking behind foraging dolphins for up to one and a half hours (mean ± s.e. = 23 min ± 2.3). Observations suggest that the relationship between gannets and whales with common dolphins was deliberate, and that these species take advantage of the superior ability of dolphins to locate and concentrate prey. The associations with gannets and whales had a significant impact on common dolphin foraging behaviour. Duration of the phenomenon was predicted to be a direct function of the quantity of prey fish available. The presence of a whale had a sizable impact on the diffusion of feeding aggregations. Results from this study indicate that the benefits of coordinated team hunts implemented by common dolphins in the Hauraki Gulf are a key factor in their foraging ecology. Their cooperative foraging skills appear to not only benefit the common dolphin individual, but other species as well. Ultimately, their role as a social hunter and an abundant, apex predator in the ocean, suggests that the common dolphin is a strongly interacting species which may facilitate population viability of other species in the Hauraki Gulf ecosystem

Comparative foraging ecology of two broad-ranging migrants, grey plover Pluvialis Squatarola and whimbrel Numenius Phaeopus (Aves: Charadrii), in tropical and temperate latitudes of the Western Indian Ocean

Bibliography: leaves 186-205.A seasonal study of the nonbreeding foraging ecology of Grey Plovers and Whimbrels was undertaken at the Zwartkops estuary, South Africa, and additional data were collected from a variety of sites in tropical and south temperate latitudes during the premigratory period. The main objective of the study was to provide comparative data on shorebird foraging ecology in the southern hemisphere, in order to contribute to the general understanding of shorebird foraging behaviour and migration patterns

Why do many animals move with a predominance of roughly forward directions?

Animal movements can influence their ecology and demographics. Animal movements are often characterized by path structures with directional persistence. The extent to which directional persistence improves forage success is investigated in this paper using theoretical simulations. It is shown that a movement strategy with directional persistence enables simulated animals to find more forage as compared to a random movement strategy. Situations where resources are chosen with certainty (optimally) are even more successful. Choosing resource with certainty cannot result in directional persistence. However, in cases where animals choose with certainty adjacent cells with resource but continue in their existing direction if none of these have resources then results include directional persistence. It is posited here that this combined strategy is the most effective because if optimal foraging works it is optimally efficient but where foraging is sub-optimal, for a variety of reasons, directional persistence will benefit foraging

Binocular vision and foraging in ducks, geese and swans (Anatidae)

Wide variation in visual field configuration across avian species is hypothesized to be driven primarily by foraging ecology and predator detection. While some studies of selected taxa have identified relationships between foraging ecology and binocular field characteristics in particular species, few have accounted for the relevance of shared ancestry. We conducted a large-scale, comparative analysis across 39 Anatidae species to investigate the relationship between the foraging ecology traits of diet or behaviour and binocular field parameters, while controlling for phylogeny. We used phylogenetic models to examine correlations between traits and binocular field characteristics, using unidimensional and morphometric approaches. We found that foraging behaviour influenced three parameters of binocular field size: maximum binocular field width, vertical binocular field extent, and angular separation between the eye-bill projection and the direction of maximum binocular field width. Foraging behaviour and body mass each influenced two descriptors of binocular field shape. Phylogenetic relatedness had minimal influence on binocular field size and shape, apart from vertical binocular field extent. Binocular field differences are associated with specific foraging behaviours, as related to the perceptual challenges of obtaining different food items from aquatic and terrestrial environments

Living in the tropics: the foraging ecology of the masked booby in the Pacific Ocean

Tropical regions represent half of the oceans on earth, yet our understanding of the ecological interactions in these areas lags far behind that for temperate or polar regions. By studying the foraging ecology of seabirds, ecological information about remote tropical regions can be obtained. However, in order to interpret the foraging ecology of seabirds, it is necessary to take account of local oceanography, inter-annual variations in environmental conditions at the colonies, and the sex and breeding stage of the birds. In this study, I used the masked booby Sula dactylatra as a model species to analyze the effects of the aforementioned factors and their interactions on the foraging ecology of a pantropical distributed seabird. Fieldwork was conducted at two remote islands in the Pacific, Motu Nui and Clarion Island, during consecutive years (2016 and 2017 at Motu Nui and 2016, 2017 and 2018 at Clarion Island), using GPS, time-depth recorders, diet samples, and satellite data, and taking account of the sex and breeding stage of the individuals. Masked boobies did not utilize the specific hydrographic features at Motu Nui and Clarion Island while foraging. Nor did they change their foraging behavior between years, likely because of relatively stable environmental conditions across years at both study sites. Notably, the El Niño event 2016 did not have a major effect on the environmental conditions at Clarion Island. While foraging trip parameters did not differ between sexes, isotopic signatures of females differed from those of males at Motu Nui. This suggests that, even when the sexes use the same areas, females may be feeding at a different trophic level than males. Foraging trip duration of birds at Motu Nui was affected by breeding stage: they foraged almost twice as long during incubation as during chick rearing. Masked boobies at Motu Nui foraged closer to their colony than those at Clarion Island, which was related to colony size but not to local environmental predictors such as chlorophyll-a concentrations. This study provides the first description of the foraging ecology of a seabird species at Motu Nui and Clarion Island, and demonstrates the value of local studies for providing information on underexplored pelagic areas. Similar to the findings of studies on the foraging ecology of tropical seabirds elsewhere, Motu Nui and Clarion Island seascape did not provide any specific areas where prey species accumulated. The unusual environmental stability around Motu Nui and Clarion Island, may maintain local availability of the main prey species of masked boobies even between El Niño events, which may explain the observed consistency in foraging parameters across years. Consistent with previous studies, masked boobies showed few sex-specific differences in their foraging ecology. However, the difference in isotopic signatures between sexes is in contrast to previous reports that found no differences between male and female masked boobies, and therefore merits further investigations. Given that breeding stage affects foraging behavior, future studies should aim to use data from birds at the same breeding stage when comparing foraging parameters between sites or years. The results from this study also confirm that seabirds from larger colonies are forced to travel further during foraging trips as a result of prey depletion closer to the colony due to continuous exploitation by a larger number of individuals. In summary, this study corroborates that local oceanography, inter-annual variations in environmental conditions at the colonies, and the sex and breeding stage of the individual need to be considered when interpreting the foraging ecology of seabirds. The findings presented in this thesis are important for interpreting the foraging ecology of masked boobies and other tropical seabird species breeding on remote islands elsewhere. They contribute to our understanding of complex food-webs in marine ecosystems, and thus are vital information for decision makers in marine spatial planning, management and conservation

THE ROLE OF LOCAL AND REGIONAL FACTORS IN THE FORAGING ECOLOGY OF BIRDS ASSOCIATED WITH POLYLEPIS WOODLANDS

Understanding the extent to which patterns of functional structure are repeated in space and the scale at which different factors (local and regional) operate to explain community patterns are of important in community ecology. I studied the extent of spatial variation in foraging ecology of birds in the Polylepis community, a vegetation system of the Andes, in regard to variation in local (vegetation structure, floristic composition, food resources) and regional factors (biogeography). Specifically, I studied foraging ecology of nine insectivorous bird species (and the assemblage they conform) across twelve disjunct woodlands embedded in three biogeographic regions of the Peruvian Andes. I examined spatial variation in foraging ecology at species level by assessing intraspecific variation in two foraging niche components: niche breadth, a relative measure of how specialist or generalist is a species relative to other species in the community; and niche plasticity, a measure of how restricted or plastic are intraspecific regularities in the niche. Results indicate that foraging strategies of birds varied from specialist-restricted to generalist-plastic. Moreover, foraging strategies seemed to be influenced mostly by fluctuations in local factors, in particular food resources. Lack of variation in foraging of the specialist-restricted species, despite fluctuations in local factors across Polylepis woodlands, may be a consequence of past events in the evolutionary history of the species that set a limit to the range of possible responses within a population, constraining the foraging niche. Lastly, I assessed the extent of spatial variation in the structure of avian assemblages using the guild approach, and focused on a) the relationship between food resource abundance and richness and abundance of birds within guilds; and b) the role of competition, using null models to determine if niche overlap in the assemblages were consistent with competition theory. Results revealed that guilds were largely consistent across woodlands but the number and identity of species associated with each guild was not so, which could be attributed to regional differences in species richness and intrapopulation variation in foraging ecology. Assemblage structure was not consistent with classic competition theory, but food resources were relatively more important in explaining patterns

Using a spatial overlap approach to estimate the risk of collisions between deep diving seabirds and tidal stream turbines : a review of potential methods and approaches

Peer reviewedPublisher PD

Taking movement data to new depths : Inferring prey availability and patch profitability from seabird foraging behavior

Funded byNatural Environment Research Council. Grant Number: NE/K007440/1 and Marine Scotland Science and Seabird Tracking and Research (STAR) Project led by the Royal Society for the Protection of Birds (RSPB)Peer reviewedPublisher PD