Contrasting phenological and demographic responses of Atlantic Puffin (Fratercula arctica) and Razorbill (Alca torda) to climate change in the Gulf of Maine

The Gulf of Maine is warming faster than most of the world’s ocean and is also the southern-most limit for nesting, cold-adapted Atlantic Puffin (Fratercula arctica) and Razorbill (Alca torda). Beginning in 1995, the Atlantic Laboratory for Avian Research has collected annual data on phenology, productivity, and fledgling body condition for puffins and Razorbills nesting at Machias Seal Island. Here, we aimed to quantify changes in these measures of breeding performance and assess whether they are related to environmental conditions. As predicted, we found that all measures of breeding performance (except puffin fledge date) have changed between 1995 and 2020, and in many cases, puffins and Razorbills are responding differently. Specifically, hatch date has retreated for puffins (occurring approximately 1 week later in 2011–2020 than in 1995–2004) and advanced for Razorbills (occurring approximately 1 week earlier in 2011–2020 than in 1995–2004). We found that environmental conditions were important predictors for measures of breeding performance, but importance of environmental conditions differ both between the species and among the measures of breeding performance. As the climate continues to warm, we expect continued changes in breeding performance of puffins and Razorbills. Further research is needed to understand the reasons for differences between the 2 species and the impacts of continued warming.

What can seabirds tell us about the tide?

Small global positioning system (GPS) trackers are now routinely used to study the movement and behaviour of birds at sea. If the birds rest on the water they become “drifters of opportunity” and can be used to give information about surface currents. In this paper, we use a small data set from satellite-tracked razorbills (Alca torda) in the Irish Sea to test the potential of this idea for measuring tidal currents. Razorbills regularly rest on the sea overnight and their tracks at this time are consistent with their drifting with the tidal flows and changing direction as the flood turns to ebb and vice versa. Data from 4 years (2011–2014) have been binned in a geographical grid and analysed to give the variation of current over a mean tidal cycle in each grid element. A map of maximum current speed is consistent with a numerical model of the tidal currents in the region. The root mean square difference between observed maximum speed and that predicted by the model is 0.15 m s−1, about 15 % of typical current speeds in the area. The divergence between bird-track speed and model prediction increases in regions of the fastest tidal currents. The method clearly has its limitations, but the results of this study show that tagged birds resting on the sea have potential to provide relatively inexpensive quantitative information about surface tidal currents over an extended geographical area.

Population trends and status of four seabird species (Uria aalge, Alca torda, Larus fuscus, Larus argentatus) at Stora Karlsö in the Baltic Sea

The island of Stora Karlsö hosts the largest colonies of fish-eating seabirds in the Baltic Sea. However, recent and reliable estimates of the number of breeding pairs of the main species have been missing. Based on a complete census in 2014, we estimated the number of Common Guillemots Uria aalge to 15,700 pairs, more than half (up to 70%) of the Baltic Sea population. The number has almost tripled since the early 1970s and the increase has been particularly strong the last 11 years, with an annual increase of 5.1%. We counted 24,600 individual adult Razorbills Alca torda and estimated it to correspond to a maximum of 12,300 pairs in 2015–2016 (census over two seasons). The colony has grown strongly; on average by 5.6% annually since the early 1970s, and Stora Karlsö now hosts up to 30% of the Baltic Sea population. Stora Karlsö also hosts colonies with about 300 pairs each of Lesser Black-backed Gull Larus fuscus and Herring Gull Larus argentatus. The gulls’ trends are negative, with an average annual decline the last 10-year period by 5.0% and 6.2%, respectively.