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The principal aims of this study, outlined in section 1.9, can be posed as a series of research questions, the concise answers to which summarise the main findings: 1. How does the central place constraint affect spatial and habitat use during different breeding stages?

Use of space by breeding black-browed albatrosses is inversely related to distance from the colony, reflecting the associated increase in time and energy costs. Hence, habitat accessibility can be approximated by the reciprocal of colony distance (Chapters 2 and 3). During incubation, trip duration is ultimately limited by the incubating partner’s ability to fast on the nest and, as a result, long trips are made (median maximum colony distance 995 km, range 54-3039 km). During post-brood the energetic demands of the growing chick are limiting and so shorter trips, closer to the colony, are made (median maximum colony distance 304 km, range 24-2949 km).

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2. What mesoscale oceanographic foraging habitats do breeding black-browed albatrosses use and which are preferred?

Analysis of individual movement data from 163 black-browed albatrosses satellite- tracked from eight colonies located throughout the species’ range (Chapter 2)

confirmed that while breeding, this species primarily forages in neritic and upper shelf slope waters. However, birds from some populations also used highly dynamic oceanic waters, characterized by high mesoscale variability. In decreasing order, bathymetric habitat preferences are for neritic (0-500 m), shelf-break to upper shelf-slope (500 – 1000 m), and then oceanic (>1000 m) waters: Preference also increased with sea floor slope, reaching a maximum at 3° (Figures 2.10 and 2.11).

3. Does habitat use and preference differ between breeding stages, populations and closely related species?

Habitat use and preferences differed between incubation and post-brood (Chapter 2). During incubation, black-browed albatrosses spent more time in subtropical waters, indicated by SSTs of 5 - 16°C. This was because, in addition to the bathymetric preferences outlined above, SST preference peaked at 16°C. While black-browed albatrosses from all populations in this study foraged primarily in either local or distant neritic waters during breeding, those from colonies other than in the Falkland Islands also foraged in oceanic waters. This propensity was most marked in birds from South Georgia, which foraged in the Antarctic Polar Frontal Zone and the Brazil-Malvinas Confluence. This was indicated by the Eddy Kinetic Energy preference of birds from this population, which was uniform up to 250 cm2/s2 and then increased linearly above this value. During post-brood, the closely-related Campbell albatross also foraged in both neritic and oceanic waters. Although their habitat preference decreased with depth, it differed from black-browed albatrosses’ by the absence of a marked preference for neritic waters. Furthermore, Campbell albatrosses also showed a

preference for positive sea level anomalies (peaking at ~ 9 cm), indicating a preference for foraging in mesoscale eddies associated with the Subantarctic Front and Antarctic Polar Frontal Zone.

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4. Do albatrosses modify their spatial usage in response to intraspecific competition from neighbouring populations?

This was only to a limited extent. During incubation, the foraging ranges of black- browed albatrosses from neighbouring colonies tend to overlap extensively (Chapter 2). However, during post-brood habitat preferences have two minima, the first in the immediate vicinity of neighbouring colonies and the second at ~ 700 km from the next nearest colony. These preferences are reflected by an avoidance, during post-brood, of areas immediately surrounding neighbouring colonies and of foraging zones of neighbouring populations at the meso to macroscale. Despite these effects, there was still some overlap in the foraging areas of birds from adjacent populations.

5. Is it possible to use individual movement and environmental data to estimate the spatial usage of foraging albatrosses from different populations?

Breeding albatrosses are central place foragers and thus habitat accessibility decreases as a function of colony distance. Hence, spatial usage was modelled as a function of habitat accessibility as well as of habitat preference and intraspecific parapatric competition. In this way it was possible to estimate the density of breeding black- browed albatrosses at both regional and global population levels (Chapter 2). The validity of this approach was demonstrated by K-folds cross validation, as well as by the close agreement between estimated spatial usage and satellite-tracking data from a colony excluded from the original analysis. However, the models exhibited some residual spatial autocorrelation. While this can result from conspecific attraction (flocking) it may also indicate that the selected covariates did not capture all of the variability in spatial usage, suggesting that the models could be further refined, perhaps by the inclusion of additional covariates or an improved accessibility function.

6. Does prey availability or intraspecific competition during the breeding season regulate population sizes?

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Breeding season prey availability, but not intraspecific competition regulates regional black-browed albatross population size (Chapter 3). When populations are regarded as comprising spatial clusters of colonies, population size was log-linearly related to the extent of preferred neritic waters and the total available Net Primary Production (NPP), which are proxies for prey availability. The strength of the relationship with population size is greater when either preferred habitat or NPP are inversely weighted by colony distance, indicating that habitat accessibility is also limiting. The intensity of

competition between adjacent populations does not explain population size well. Therefore, although individual colony sizes may vary in response to parapatric

intraspecific competition, regional population size is unaffected. However, at the level of individual colonies this and other factors, including nesting habitat availability, may be limiting.

7. Does the wind field affect the flight performance of albatrosses and therefore limit habitat accessibility?

The groundspeed of albatrosses in direct flight is linearly related to the wind speed component in the direction of flight. Relative flight direction is more important in determining groundspeed than absolute wind speed (Chapter 4). When relatively unconstrained (e.g. in mid-foraging trip), all species (wandering, black-browed, grey- headed and light mantled albatrosses) tend to fly predominantly across the wind. However, commuting birds sometimes encounter headwinds during outward trips and tail winds on their return and consequently groundspeed is 1.0 – 3.4 m/s faster during the return.

8. Could differences in flight performance between species and sexes mediate spatial segregation?

There are significant differences in the effects of wind on the groundspeeds of different species and sexes (Chapter 4). Wandering albatrosses are more affected by wind than black-browed, light-mantled and grey-headed albatrosses. Furthermore, the

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related to sexual size dimorphism, as males are larger and have higher wing loadings than females. However, no evidence was found that this led to sexual segregation, as males and females experienced comparable wind speeds during foraging trips.