It matters where you eat: seabird foraging strategies alter their responses to climate change

Arctic temperatures are warming faster than the rest of the world

Global climate change, including climate warming, has been causing changes all across our globe. In the arctic, temperatures are warming faster than in other places due to arctic amplification. Arctic amplification is related to the melting of sea ice, which usually reflects sunlight and its energy back in to the atmosphere. As temperatures warm and ice melts, there is less ice surface to reflect sunlight back into the atmosphere which means that the energy is absorbed into the water, leading to even more rapid warming.

Many of us have seen pictures or videos of polar bears that rely on sea ice for hunting either in poor physical health or wandering around an ice-free arctic landscape. These pictures are hard to look at and invoke strong emotions in many, but they illustrate the dramatic changes that have been occurring in the Arctic. One significant change that could have dramatic consequences for the creatures living in the Arctic is the timing of spring. As temperatures warm, sea-ice melts and spring arrives earlier in the year.

The arrival of spring is critical for species. It signals the start of more favorable temperatures and an increase in food. One of the classic signals of the arrival of spring in the ocean is the spring phytoplankton bloom. Phytoplankton, which are microscopic algae, are the base of many food webs in the ocean and their presence fuels an increase in the other trophic levels such as invertebrates and fishes. Arctic seabirds rely on these organisms for food in the spring and also use its arrival to time their reproduction.

Seabirds that forage in the ocean surface are reproducing earlier in the spring

Sébastien Descamps of the Norwegian Polar Institute and his colleagues from Spain, Norway, the United States, Canada, and France recently published a study that details how the timing of reproduction in Arctic seabirds is being impacted by the increasingly earlier arrival of spring. They were particularly interested in understanding if the length of the breeding season or foraging strategy impacted seabird responses.

Deschamps and his colleagues compiled data from 36 breeding location and 29 species of seabirds that spanned a 35 year time frame from 1982-2016. The data represented species with different foraging strategies and breeding season duration as well as breeding locations in the Pacific and the Atlantic Oceans (see Deschamps et al. 2019 Figure 1 which is available to free online).

To determine how foraging strategy might impact the timing of reproduction, Descamps and his colleagues separated seabirds into three foraging strategies: surface feeders that forage in the upper 1-2 m (3-6 feet) of the water column, pelagic divers that dive deep into the water column and can feed from different depths, or benthic divers that dive to the bottom of the ocean and forage on creatures that live there.

The findings showed that surface feeders had advanced the timing of their reproduction, while there was little change in the timing of reproduction in diving seabirds. These results suggest that diving feeders may be less sensitive to environmental change because they can utilize a larger area for foraging, may have more flexibility in their diet, or their reproduction may be driven by factors that have not changed over the course of the study and not the onset of spring. Interestingly, the advancement of breeding of surface feeding seabirds was only significant in the Pacific region where birds breed on average 10 days earlier in 2016 than they did in 1982. This results reflects the fact that spring has been advancing in the Pacific but not in the Atlantic Arctic due to different oceanographic and atmospheric conditions.

Deschamps and colleagues also investigated differences in birds with different breeding season duration which they assigned as less than 50 days, between 50 and 80 days, or more than 80 days. Their results showed that birds with longer breeding seasons showed a greater response to spring advancement although the effect was small. Nonetheless, the results of the present study suggest that the response of seabirds to climate change is complex and depends on where they live, the length of their breeding strategy, and where the eat.

Feature Image: Pixabay

Source Article: Sébastien Descamps, Franciso Ramírez, Sigurd Benjaminsen, Tycho Anker-Nilssen, Robert T. Barrett, Zofia Burr, Signe Christensen-Dalsgaard, Kjell-Einar Erikstad, David B. Irons, Svein-Håkon Lorentsen, Mark L. Mallory, Gregory J. Robertson, Tone Kirstin Reiertsen, Hallvard Strøm, Øystein Varpe, and Sébastien Lavergne. Diverging phonological responses of Arctic seabirds to an earlier spring. Global Change Biology 25, 4081-4091. https://onlinelibrary.wiley.com/doi/epdf/10.1111/gcb.14780