**Abstract:**

According to niche theory, sympatrically breeding species with similar diets frequently show foraging niche partitioning to decrease inter-specific competition, e.g. through temporal or spatial separation, or foraging specialisation. In this study, using stable isotope analyses, we aimed to assess the extent of niche overlap, differences in niche width and the relationship between isotopic signatures and chick growth in two sympatric storm-petrel species, Fregetta tropica (BBSP) and Oceanites oceanicus (WSP) breeding in Maritime Antarctica. We analysed δ15N and δ13C in chick down (pre-laying maternal diet), chick feathers (under tail coverts, UTC; current diet) and adult blood (current diet), and δ18O in UTC. We found isotopic (N, C) niche overlap (proportion (± confidence interval) of the standard ellipse area intersection relative to BBSP and WSP areas) for blood (BBSP 0.39 ± 0.18; WSP 0.10 ± 0.05) and down (BBSP 0.57 ± 0.19; WSP 0.26 ± 0.11), but a lack thereof for UTC (BBSP 0.05 ± 0.13; WSP 0.01 ± 0.03). We found wider isotopic niches for WSP compared to BBSP in all three tissues, indicating differences in foraging flexibility between the species. In both species body mass growth was negatively correlated with δ15N (in UTC for BBSP and in down for WSP). Tarsus growth was positively correlated with δ18O in WSP. We found no correlations for δ13C. The observed niche overlap between BBSP and WSP adults during the pre-breeding (down) and chick-rearing (blood) phases can be explained by their reliance on superabundant Antarctic krill (Euphausia superba). Despite similar chick growth rates in both species, BBSP chicks were fed a more nutritious diet, as implied by higher δ15N values, and the more frequent occurrence of fish in BBSP regurgitations reported in previous studies. While the highly productive Antarctic environment might reduce inter-specific foraging competition, chick nutrition requirements might force parents to be more selective in chick prey selection.

**Authors:**

Anne Ausems¹, Grzegorz Skrzypek², Katarzyna Wojczulanis - Jakubas¹, Dariusz Jakubas¹

¹University of Gdansk, ²The University of Western Australia (M090)

Sharing menus or kids specials? Inter- and intraspecific differences isotopic niches between sympatrically breeding storm-petrels

**Session Replay:** [Click here](https://zoom.us/rec/share/CUDsOhZHuZyl22I9D8nlRBtDpoWlhKWbzRpLKocsg0RGkdlnQs3bYiUr4-Ygj05b.-WmPT8ntSWSQBkyv?startTime=1633521614000)<br><br>

<i>**Session Chair: **Sophie Bennett </i><br><br> 



Biology & Breeding/Non-breeding biology I

technical paper

Welcome Seabirders!  

Welcome to Virtual World Seabird Conference 3 - vWSC3! Whether you are in your office or lab, at home, in a coffee shop or bar poaching some wifi, or at a remote field site or research vessel – we are very excited to welcome you to the third ever World Seabird Conference. 

We would like to thank ALL of you for being so patient as WSC3 was scheduled, postponed, rescheduled, revised to virtual, and scheduled again. Throughout all those iterations there was one message that remained perfectly clear – seabirders were eager to meet and share their science. If we could not meet in person then virtual it would have to be, but a 3rd WSC was something everyone wanted. That support and commitment helped the WSU Board of Directors and Member Societies sort through all of the challenges they faced to plan and hold this conference. 

The list of those that need to be thanked is long and, while we plan on recognizing many during the live closing plenary, it is important to do so here in writing as well. 

The Australasian Seabird Group was our Local Host for our plan to meet in Hobart, Tasmania. They invested substantial time and effort to find venues and plan events that we unfortunately were not able to visit. Nonetheless we appreciate their work on behalf of WSC3 and encourage all of you to thank them when you see their members in Gathertown or elsewhere during our virtual meeting. Their willingness to host created the initial excitement for WSC3 and without that our vWSC would not have been possible.

We also wish to thank the Science Program Committee, the Virtual Committee, and the Early Career Scientist Committee for their hard work planning the logistics, events, and schedule for vWSC3. These committees also had to deal with changing parameters and short timelines that made what is always a challenging task even more challenging. The Travel Awards Committee also invested time and effort in developing procedures for awarding travel funds that ultimately would not be implemented. 

Our ability to shift from an in-person to a virtual meeting, and to do so in a way that would be financially feasible, was due to the effective efforts of The International Fundraising Committee and to our financial sponsors. The IFC raised funds to support WSC3 and then, through the good relationships they built with sponsors, ensured we could re-envision how those funds could be used to support a virtual conference that would be affordable and high-quality.

We all owe the WSU Board of Directors and the Representatives of the Member Societies a great deal of thanks. They are the ones who manage the WSU and, for the past 18 months, have had to have a series of challenging meetings and conversations, have had to make a series of difficult choices, have had to do all of that while considering the short- and long-term health of WSU and the World Seabird Conferences, and did this while also managing their own challenges at their day jobs. We are grateful for their diligence, patience, foresight, and throughout all of the meetings, their collegiality. Also – a 6-year term is quite a commitment!

There would not be a WSC3 without a successful WSC1 and WSC2. Thanks go to the Pacific Seabird Group for their support of WSC1 in Victoria, Canada, and to the African Seabird Group for their support of WSC2 in Cape Town, South Africa. In each of these endeavors and for our current conference we were fortunate to work with a dependable and trustworthy partner in Podium Conferences. Michelle Smith and Marischal de Armond have become valued members of our team and have not only helped us plan conferences but have assisted and advised the WSU Chairs and Board on issues above and beyond conference planning. 

As we embark on our vWSC3 week we extend to all of you our thanks for showing up, for being patient, and most importantly for the work you do with seabirds. We are all part of a unique, global community that shares an interest, a fascination, and a passion for birds that make a living in our world’s oceans. We have advanced the science, conservation, and management of seabirds as well the ecosystems they inhabit. We are consistently impressed and motivated by the work you do. 

The WSU formed in 2010 because we saw the need for a global organization to address challenges at a global level. Over the past 11 years WSU has grown, adapted, and evolved to become the community that this week is making vWSC3 a reality. Enjoy the week, appreciate and support the friends and colleagues you have made in the community, and if you see us in a virtual hallway please stop and say hello! 

Thank you for the opportunity to serve all of you and the WSU over the past few years,

Nicholas Carlile, Interim Chair, WSU<br>
Patrick Jodice, 2nd Chair of the WSU<br><br>

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3rd World Seabird Conference

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Anne Ausems

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Sharing menus or kids specials? Inter- and intraspecific differences isotopic niches between sympatrically breeding storm-petrels

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