Inter-annual changes in oceanic conditions drives spatial and trophic consistency of a tropical marine predator

Influence of paternal factors on plastic ingestion and brominated chemical exposure in East Tropical Atlantic Procellariid chicks

The presence of plastic debris and organo-brominated compounds in the marine environment poses a concern to wildlife. Plastic can absorb and release chemical compounds, making their ingestion potentially harmful, while chemical compounds have become omnipresent, with a tendency to bioaccumulate in the food web. Seabirds are often used as indicators of marine plastic pollution, yet studies on the exposure of tropical communities to plastic contamination are still scarce. In this study we monitored the amounts of plastics in faeces and organo-brominated compounds ingested/assimilated in feathers by adults and chicks of Cape Verde shearwaters and Bulwer's petrels from Cabo Verde. Anthropogenic pollutants, polybrominated diphenyl ethers (PBDEs), and naturally generated methoxylated-PBDEs (MeO-PBDEs) were among the probed compounds. The frequency of plastic debris ingestion was similar in both species' adults and chicks, although, the characteristics of the ingested plastic differed. Frequency and number of microplastics increased throughout the nestling season for chicks from both species. All species and age groups showed the presence of PBDEs and MeO-PBDEs. Among PBDEs, Bulwer's petrels exhibited higher concentrations than Cape Verde shearwaters, and chicks had higher concentration profiles than adults. Specifically, Bulwer's petrel chicks showed higher concentrations than Cape Verde shearwater chicks. On the contrary, Cape Verde shearwater adults exhibited higher occurrence and concentrations of MeO-PBDEs when compared to Cape Verde shearwater chicks. We found no effect of plastic loadings or loadings of organohalogen contaminants on body condition or size, although harmful effects may be hidden or reveal themselves in a medium- to long-term. Feather samples from both adults and chicks were shown to be useful for comparing intraspecific contamination levels and appear suitable for the long-term assessment of organohalogen contaminants in seabirds. Species-specific foraging and feeding strategies are likely the drivers of the observed variation in organochlorine contamination burdens among seabird species.

Boldness predicts foraging behaviour, habitat use and chick growth in a central place marine predator

Animal personality can shape individual's fitness. Yet, the mechanistic relationship by which individual's personality traits lead to variations in fitness remains largely underexplored. Here, we used novel object tests to measure boldness of chick-provisioning Cory's shearwaters (Calonectris borealis) from a coastal colony off west Portugal, and deployed GPS loggers to study their at-sea behaviour and distribution. We then tested whether boldness predicts individual differences in adult's trophic ecology and variations in chick growth, to assess potential implications of personality-specific foraging behaviours. Foraging effort was higher for shyer than for bolder individuals, which, during short forays, exhibited larger foraging ranges, and foraged in regions of higher and more variable bathymetry. This suggests that nearby the colony bolder individuals expanded their foraging area to maximize resource acquisition and increase the probability of foraging success. When endeavouring to longer distances, bolder individuals exhibited comparably shorter foraging ranges and targeted low bathymetry regions, likely with enhanced prey availability, while shyer individuals exhibited much larger foraging ranges indicating greater flexibility when foraging in oceanic realms. Despite such differences between bolder and shyer individuals their isotopic niches were similar. Yet, chicks raised by bolder parents grew at a faster rate than those raised by shyer parents. Together, our results suggest that differences in resource acquisition strategies could play a key role through which individual's boldness may influence breeding performance, even when individuals have similar isotopic preferences.

Microplastics ingestion and endocrine disrupting chemicals (EDCs) by breeding seabirds in the east tropical Atlantic: Associations with trophic and foraging proxies (δ15N and δ13C)

In this study we found that endocrine disrupting chemicals (EDCs) were omnipresent in a tropical seabird community comprising diverse ecological guilds and distinct foraging and trophic preferences. Because EDCs tend to bioaccumulate within the food web and microplastics can absorb and release harmful chemical compounds, our findings draw attention to the potential threats to wildlife. Thus, the goal of this study was to investigate the role of plastic ingestion, trophic and foraging patterns (δ15N and δ13C) of five tropical seabird species breeding in sympatry, on the exposure to EDCs, namely Polybrominated diphenyl ethers (PBDEs), methoxylated polybrominated diphenyl ethers (MeO-PBDEs) and personal care products (PCPs, e.g., musk fragrances and UV-filters). Results indicated that microplastics occurrence and EDCs detection frequency varied among species. Microplastics occurrence was higher in species with dual and coastal foraging strategies. Preen oil had higher levels of MeO-PBDEs and PCPs, while serum had higher levels of PBDEs. In brown boobies, the correlation between microplastics and ∑PBDEs levels was significant, suggesting that microplastics ingestion is a key PBDEs route. Trophic position (δ15N) plays a key role in PBDEs accumulation, particularly in Bulwer's petrel, which occupies a high trophic position and had more specialized feeding ecology than the other species. MeO-PBDEs were linked to foraging habitat (δ13C), although the link to foraging locations deserves further investigation. Overall, our findings not only fill key gaps in our understanding of seabirds' exposure to microplastics and EDCs, but also provide an essential baseline for future research and monitoring efforts. These findings have broader implications for the marine wildlife conservation and pollution management in sensitive environments, such as the tropical regions off West Africa.

Anthropogenic debris ingestion in a tropical seabird community: Insights from taxonomy and foraging distribution

Oceans have been considered as an unlimited supply of goods and services, but resource extraction and waste disposal became ubiquitous and have been damaging the health of marine ecosystems. Finding suitable sentinel species of the human impacts on the oceans is thus imperative, since they may work as early warnings of disruptive situations. In this study, we investigated how taxonomy and foraging distribution influenced the occurrence of anthropogenic debris among five seabird species inhabiting the tropical Atlantic region. Occurrence of anthropogenic debris was assessed using faeces of breeding individuals as a proxy of ingestion. A total of 268 particles were extracted from all samples. The categories "fragments" and "fibres", as well as the colour "blue", were the most prevalent characteristics across species. There was a high diversity of polymers from cellulosic particles to synthetic plastics (Anthropogenic Cellulosic 26.9 %; Polyester 7.7 %; Varnish 5.8 %; Polypropylene 1.9 %). Species with a more coastal foraging strategy exhibited higher occurrence and number of anthropogenic debris when compared to species foraging comparably more in pelagic areas. This suggests that anthropogenic debris are more prevalent in coastal foraging areas, where human activities occur in higher number and frequency (e.g., fisheries) and sources of freshwater input from inland are at close distance. These results provide more evidence to the growing perception on the ubiquity and diversity of anthropogenic debris in the marine environment, and further support the usefulness of using seabirds as bio-indicators of anthropogenic pollution in both neritic and oceanic regions.

Omega-3 enriched chick diet reduces the foraging areas of breeders in two closely related shearwaters from contrasting marine environments

Seabirds have evolved several life-history characteristics to help buffer environmental stochasticity. However, particularly during the breeding season, seabirds may be affected by reductions in prey availability and localised oceanographic conditions caused by variations in the environment. The increase in sea surface temperature, triggered by accelerated global warming, is impairing phytoplankton production of omega-3 fatty acids (FAs). Here, we assessed the ecological role of omega-3 FAs on chick development and subsequently on breeder foraging behaviour in two closely related shearwater species foraging in contrasting marine environments. We supplemented chicks with omega-3 FA pills or with control placebo pills and monitored chick growth, chick health status and breeder at-sea foraging behaviour using global positioning system devices. We found that omega-3 chick supplementation reduced the 95% kernel utilization distribution of short trips of Cape Verde shearwaters, but overall, breeders kept a similar foraging pattern between treatments, potentially influenced by predictable prey patches off the West African coast. In contrast, for Cory's shearwaters, the parents of the omega-3 group greatly reduced the foraging effort. This suggests that the proximity to productive prey patches around the colony may help birds to adjust their effort and, therefore, energy expenditure, to changes in the development of their offspring, as driven by their nutritional status. Overall, our results suggest a link between a chick diet enriched in omega-3 FAs and parental foraging effort, providing insight into their ability to cope with a changing and increasingly stochastic marine environment.

Chick Provisioning in Grey-Faced Petrel (Pterodroma gouldi) under Environmental Stress

Grey-faced Petrels (Pterodroma gouldi) are colonial burrowing seabirds predominantly nesting on offshore islands of the upper North Island of New Zealand. We studied their chick provisioning on Te Hāwere-a-Maki during two years of unfavourable warmer La Niña conditions in 2011 and 2013. We intensively monitored chicks in each year, weighing chicks every 12 h for 10 consecutive days to estimate meal sizes following chick provisioning and to estimate 12-hourly body mass loss as a function of time since last feeding. We found a quadratic relationship of body mass loss with time since last feeding, with rapid digestion of meals following provisioning followed by a period of fasting from five days post feeding as chicks waited an unknown and variable amount of time until their next meal. The rate of body mass loss did not depend on chick age nor body mass, and did not differ between years, but heavier chicks included in our study were more likely to successfully fledge, suggesting a legacy of adult provisioning prior to our study commencing. Our regular handling of chicks for monitoring has no discernible impact on parent provisioning compared to a set of control chicks. The mean estimates of 100-gram meal sizes and 10-day foraging trip durations are likely to be below the break-even point for this species.

Individual consistency in migration strategies of a tropical seabird, the Round Island petrel

BACKGROUND

In migratory species, the extent of within- and between-individual variation in migratory strategies can influence potential rates and directions of responses to environmental changes. Quantifying this variation requires tracking of many individuals on repeated migratory journeys. At temperate and higher latitudes, low levels of within-individual variation in migratory behaviours are common and may reflect repeated use of predictable resources in these seasonally-structured environments. However, variation in migratory behaviours in the tropics, where seasonal predictability of food resources can be weaker, remains largely unknown.

METHODS

Round Island petrels (Pterodroma sp.) are tropical, pelagic seabirds that breed all year round and perform long-distance migrations. Using multi-year geolocator tracking data from 62 individuals between 2009 and 2018, we quantify levels of within- and between-individual variation in non-breeding distributions and timings.

RESULTS

We found striking levels of between-individual variation in at-sea movements and timings, with non-breeding migrations to different areas occurring across much of the Indian Ocean and throughout the whole year. Despite this, repeat-tracking of individual petrels revealed remarkably high levels of spatial and temporal consistency in within-individual migratory behaviour, particularly for petrels that departed at similar times in different years and for those departing in the austral summer. However, while the same areas were used by individuals in different years, they were not necessarily used at the same times during the non-breeding period.

CONCLUSIONS

Even in tropical systems with huge ranges of migratory routes and timings, our results suggest benefits of consistency in individual migratory behaviours. Identifying the factors that drive and maintain between-individual variation in migratory behaviour, and the consequences for breeding success and survival, will be key to understanding the consequences of environmental change across migratory ranges.

Foraging costs drive within-colony spatial segregation in shearwaters from two contrasting environments in the North Atlantic Ocean

Foraging spatial segregation is frequent in central-place foragers during the breeding season, but very few studies have investigated foraging spatial segregation between adjacent sub-colonies. Here, we assessed for within-colony differences in the at-sea distribution, habitat use, trophic ecology and chick growth data of two Calonectris colonies differing in size, and breeding in two different environments in the North Atlantic Ocean. For this, we GPS tracked 52 Cory's shearwaters (Calonectris borealis) breeding in 2 small sub-colonies at Berlenga Island (Portugal) and 59 Cape Verde shearwaters (Calonectris edwardsii) breeding in 2 sub-colonies differing greatly in size at Raso Islet (Cabo Verde), over 2 consecutive breeding seasons (2017-2018), during chick-rearing. Cory's shearwaters from the two sub-colonies at Berlenga Island broadly overlapped in repeatedly used foraging patches close to the colony. In contrast, the foraging distribution of Cape Verde shearwaters was partially segregated in the colony surroundings, but overlapped at distant foraging areas off the west coast of Africa. Despite spatial segregation close to the colony, Cape Verde shearwaters from both sub-colonies departed in similar directions, foraged in similar habitats and exhibited mostly short trips within the archipelago of Cabo Verde. These results, corroborated with similar trophic ecology and chick growth rates between sub-colonies, support the idea that foraging spatial segregation in the colony surroundings was not likely driven by interference competition or directional bias. We suggest that high-quality prey patches are able to shape travel costs and foraging distribution of central-place foragers from neighbouring sub-colonies.

Year-round element quantification of a wide-ranging seabird and their relationships with oxidative stress, trophic ecology, and foraging patterns

Multidisciplinary approaches are essential to diligently assess environmental health status of ecosystems. In this study, year-round chemical elements' exposure and impacts were assessed on the wide-ranging Cory's shearwater Calonectris borealis breeding in Berlenga Island, offshore Portugal, North Atlantic Ocean. The aim was to identify potential contamination and oxidative stress sources associated with trophic ecology, habitat and spatial use, and foraging patterns. A set of 20 chemical elements were quantified, along with oxidative stress biomarkers, stable isotope analyses, and GPS tracking data. Birds presented higher accumulation to some non-essential elements along the year (i.e. arsenic, As; cadmium, Cd; mercury, Hg; lead, Pb; and strontium, Sr), in which concentrations were similar or surpassed other procellariform seabird populations all over the world. No significant differences were found for any of the elements between different periods within the breeding season, with exception of Hg. However, a Principal Component Analysis taking into consideration a group of elements showed differences between pre-laying and chick-rearing periods, with overall higher concentrations in the former. Individuals spending more time engaging in an intensive search for food, and in more coastal environments, presented overall higher element concentrations, and particularly Hg. Contrary to expectations, no relationships were found between chemical elements and oxidative stress. On the other hand, spatial use and foraging patterns of Cory's shearwaters influenced their oxidative stress responses. Our results highlight the need for multidisciplinary approaches to deepen understanding of the large-scale vulnerability of bioindicators such as seabirds and, by extension, the overall environmental health of ecosystems in which they rely.

Year-round at-sea distribution and trophic resources partitioning between two sympatric Sulids in the tropical Atlantic

In the oligotrophic tropical marine environment resources are usually more patchily distributed and less abundant to top predators. Thus, spatial and trophic competition can emerge, especially between related seabird species belonging to the same ecological guild. Here we studied the foraging ecology of two sympatric species-brown booby (BRBO) Sula leucogaster (breeding) and red-footed boobies (RFBO) Sula sula (non-breeding)-at Raso islet (Cabo Verde), across different seasons. Sexual segregation was only observed during Jun-Oct, when RFBO were present, with larger females BRBO remaining closer to the colonies, while males and RFBO travelled further and exploited different habitats. Overall, species appeared to prefer areas with specific oceanic features, particularly those related with oceanic currents and responsible for enhancing primary productivity in tropical oceanic areas (e.g. Sea Surface Height and Ocean Mixed Layer Thickness). Female BRBOs showed high foraging-site fidelity during the period of sympatry, while exploiting the same prey species as the other birds. However, during the months of co-existence (Jun.-Oct.), isotopic mixing models suggested that female BRBO would consume a higher proportion of epipelagic fish, whereas female RFBO would consume more squid compared to the other birds, possibly due to habitat-specific prey availability and breeding energy-constraints for BRBO. We conclude that divergent parental roles, environmental conditions, habitat preference and competition could be mechanisms simultaneously underlying sexual segregation for BRBO during a period of co-existence, while inter-specific foraging differences appear to be more affected by habitat preference and different breeding stages. These results support previous statements that BRBO can adapt their foraging ecology to different circumstances of environmental conditions and competition, and that marine physical features play an important role in foraging decisions of boobies.