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Although studying the diet of threatened species is crucial in terms of conservation, the diet of the Madeiran Storm Petrel (Hydrobates castro) and the vulnerable, Azores-endemic Monteiro's Storm Petrel (H. monteiroi) is mostly unknown. The only information available to date comes from anecdotal observations, analysis of mercury levels and stable isotopes. Here is presented the first insights into prey consumption by adults and chicks from the two species breeding in the Azores Archipelago, Portugal, in the mid-Atlantic Ocean. The rapidly developing field of metabarcoding was used to identify dietary items from fecal samples, to species level where possible. A total of thirteen fish, five cephalopod, one crustacean and two oligochaete operational taxonomic units (OTUs) were detected. Results suggest that both petrel species feed mainly on myctophid fish. However, differences were detected between the prey species consumed by (i) H. monteiroi and H. castro, (ii) two distinct H. castro populations (Vila and Praia islets), and (iii) chicks and adults within the same population.

The work was funded by the Natural Environment Research Council (Standard Research Grant NE/H007466/1) and donations from Evan Fountain (In Memoriam donations for Issy Fountain) and Mike Matthewson. Marine vertebrates show a diversity of migration strategies, including sex differences. This may lead to differential demography, but the consequences of such between-sex variation are little understood. Here, we studied the migration of known-sex northern gannets Morus bassanus — a partial migrant with females ~8 % heavier than males. We used geolocators to determine wintering areas of 49 breeding adults (19 females and 30 males during 2010 to 2014) from 2 colonies in the northeast Atlantic (Bass Rock and Grassholm, UK). We also tested for sex-specific survival probabilities using capture−mark−recapture methods (n = 72 individuals Bass Rock, n = 229 individuals Grassholm; 2010−2018) and applied sex-specific population projection matrices (PPMs) to quantify population-level effects. Tracked gannets wintered in a range of large marine ecosystems (LMEs): Canary Current LME (CCLME; 69 %), Celtic-Biscay Shelf LME (16 %), Iberian Coastal LME (8 %), North Sea LME (4 %) or Mediterranean LME (2 %). Migratory destination differed between the sexes: 90 % of females vs. 57 % of males wintered in the CCLME. Survival was similar between the sexes at Bass Rock (mean ± 95 % CI = 0.951 ± 0.053 and 0.956 ± 0.047 for females and males, respectively). At Grassholm, there was evidence of slight sex differences in breeder survival: females had lower annual survival (0.882 ± 0.040) than males (0.946 ± 0.026). At Bass Rock, PPMs with no sex effect best fitted the observed population increase (1994−2014). Sex-specific PPMs fitted the population estimates for Grassholm (1995−2015). Our results reveal that female gannets are more likely to travel further than males to winter in the CCLME. This difference is unlikely due to morphological differences, unlike in other bird species. However, the reason for slightly higher over-winter female mortality at Grassholm is unclear. Publisher PDF

There is a pressing need to quantify the risks of renewable energy developments such as offshore wind farms for protected populations. However, assessments are often based on incomplete data, or fail to consider variation in risk between sexes and at different times of year. We tracked northern gannets foraging from the world's largest colony (Bass Rock, Scotland) across five consecutive breeding seasons. We examine how seasonal and sex differences in behaviour affect the collision risk from planned and operational wind farms within their foraging range and assess the likely consequences for long-term population viability. Both sexes made shorter trips during chick-rearing than prior to chick-hatching, spent a greater proportion of time within wind farm sites and had an eight times greater potential collision risk during chick-rearing. Females made longer trips than males at both these times of year, flew higher and spent more time within wind farm sites, leading to three times greater collision risk for females. After accounting for the potential additional mortality from collisions, and assuming that the death of a parent also led to the loss of its offspring, the breeding population was projected to increase by 3.57% (95% CI: 2.16–5.15%) per year, compared with 6.56% (95% CI: 4.59–8.73%) in the absence of turbines, suggesting a negligible effect on population viability. However, additional mortality could result in greater immigration from neighbouring colonies, potentially affecting their viability and highlighting a need for research within a metapopulation framework to assess the impacts of offshore wind developments on vulnerable species across multiple connected sites.