Climate oscillations drive millennial‐scale changes in seabird colony size

Abstract

Seabird population size is intimately linked to the physical, chemical, and biological processes of the oceans. Yet, the overall effects of long‐term changes in ocean dynamics on seabird colonies are difficult to quantify. Here, we used dated lake sediments to reconstruct ~10,000‐years of seabird dynamics in the Northwest Atlantic to determine the influences of Holocene‐scale climatic oscillations on colony size. On Baccalieu Island (Newfoundland and Labrador, Canada)—where the world's largest colony of Leach's storm‐petrel (Hydrobates leucorhous Vieillot 1818) currently breeds—our data track seabird colony growth in response to warming during the Holocene Thermal Maximum (ca. 9000 to 6000 BP). From ca. 5200 BP to the onset of the Little Ice Age (ca. 550 BP), changes in colony size were correlated to variations in the North Atlantic Oscillation (NAO). By contrasting the seabird trends from Baccalieu Island to millennial‐scale changes of storm‐petrel populations from Grand Colombier Island (an island in the Northwest Atlantic that is subjected a to different ocean climate), we infer that changes in NAO influenced the ocean circulation, which translated into, among many things, changes in pycnocline depth across the Northwest Atlantic basin where the storm‐petrels feed. We hypothesize that the depth of the pycnocline is likely a strong bottom‐up control on surface‐feeding storm‐petrels through its influence on prey accessibility. Since the Little Ice Age (LIA), the effects of ocean dynamics on seabird colony size have been altered by anthropogenic impacts. Subsequently, the colony on Baccalieu Island grew at an unprecedented rate to become the world's largest resulting from favorable conditions linked to climate warming, increased vegetation (thereby nesting habitat), and attraction of recruits from other colonies that are now in decline. We show that although ocean dynamics were an important driver of seabird colony dynamics, its recent influence has been modified by human interference.

Soaring migrants flexibly respond to sea-breeze in a migratory bottleneck: using first derivatives to identify behavioural adjustments over time

“…This method mainly adds a fundamental step in the use of GAMMs in time series analysis, which is the calculation of first derivatives that highlight periods of change in the modelled non-linear relationships. This method is readapted here to study how bird response changes over time, representing the first application of this method in studies of animal behaviour after it was recently used in climate and paleoclimatic change studies [46, 51, 52]. This methodology allowed us to explore whether bird flight behaviour modification as the circulation of the wind varies over time.…”

Quantifying gull predation in a declining Leach’s Storm-petrel ( Hydrobates leucorhous ) colony

“…These changes were expected to have resulted in increased predation on Leach's Storm-petrels by gulls, as they sought to bridge the nutritional gap between chicks hatching, and capelin spawning Montevecchi 1999, Stenhouse et al 2000). Though oceanographic and climatic conditions are strong drivers of Leach's Storm-petrel populations, anthropogenic influences are increasingly important (Duda et al 2022). Initial estimates in 1997 found that 49,000 storm-petrels were depredated annually on Great Island, raising concerns for the storm-petrel population's persistence (Stenhouse et al 2000).…”