Seabird colony size depends on climatic fluctuations



by LORENZO CIOTTI

Seabird colony size depends on climatic fluctuations

In the study of climate change it is necessary to consider issues pertinent to the most diverse scientific fields, therefore with typical characteristics of interdisciplinarity: meteorology, physics, oceanography, chemistry, astronomy, geography, geology and biology include many aspects related to this problem, which can therefore be considered exquisitely multidisciplinary.

In general, in the study of climate change, two distinct phases are highlighted: the detection of the climate change, generally referring to the statistical analysis of historical series of atmospheric data which therefore constitute the experimental evidence, and the attribution of the causes of this change, on the basis of targeted studies, which can therefore be natural and or anthropogenic.

Based on these studies, a natural cause is highlighted up to the last century but, starting from the middle of the twentieth century, the scientific community considers them due to human action, in the form of alteration of the greenhouse effect.

In particular, according to the Intergovernmental Panel on Climate Change's 5th Climate Change Report: "The warming of the climate system is unequivocal, and, since 1950, many of the changes observed are unprecedented in previous decades and millennia.

The atmosphere and oceans. have warmed, the mass of snow and ice has decreased, sea levels have risen, and greenhouse gas concentrations have risen. " The consequences on the understanding or not of the problems related to climate change have profound influences on human society, which must also deal with them from an economic and political point of view.

Climate oscillations drive millennial-scale changes in seabird colony size, study published on the Global change biology, said: "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 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 Is land, 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."