The decline of Norwegian kittiwake populations: modelling the role of ocean warming

Abstract

The black-legged kittiwake Rissa tridactyla is a pelagic seabird whose population has recently declined in most parts of the North Atlantic and which is red-listed in most bordering countries. To investigate a possible cause for this decline, we analysed the population dynamics of 5 kittiwake colonies along the Norwegian coast, ranging from 62° to 71°N, over the last 20 to 35 yr. By quantifying the importance of sea surface temperatures (SST) in relevant areas of the North Atlantic, we tested the importance of climatic conditions throughout the populations' annual cycles. We found no synchrony among colonies; however, SST affected population dynamics, explaining between 6% and 37% (average 18%) of the variation in annual population growth rate. While dynamics of the southerly colonies were mainly affected by winter conditions in the Grand Banks area, dynamics of the northernmost colonies were dominated by autumn conditions off Svalbard. Negative slopes indicated stronger population decline under warmer ocean conditions. Population dynamics were affected both via adult survival and offspring recruitment, as evidenced by the presence of unlagged effects as well as effects lagged by the age at recruitment. Finally, we performed population viability analyses taking into account the projected warming trends for the future. The median time to extinction of the Norwegian colonies was 52 to 181 yr without considering covariates; 45 to 94 yr when considering the effects of SST but ignoring future warming; and 10 to 48 yr when ocean warming, based on a 'business as usual' scenario, was taken into account.

Circumpolar dynamics of a marine top‐predator track ocean warming rates

“…Kittiwake populations declined rapidly in the 1990s throughout most of the species’ breeding range, corroborating results of previous studies at local scales (Frederiksen, Wanless, Harris, Rothery, & Wilson, ; Labansen, Merkel, Boertmann, & Nyeland, ; Sandvik et al., ). Changes in kittiwake population trends tracked changes in trends of spring SST around the colonies and when the ocean warming was faster, the decline in kittiwake colony size was steeper.…”

Seabirds and climate: knowledge, pitfalls, and opportunities

“…Jenouvrier et al (2005a) found that climate may have a direct or a lagged effect on population dynamics depending on environmental stochastic conditions. Some studies showed that climate have a simultaneous effects both direct and lagged because each demographic parameter are affected differently by climate Sandvik et al, 2014). Finally, the existence of non-linear relationships between climate and seabird ecological parameters has seldom been explored (e.g., Durant et al, 2004;Jenouvrier et al, 2005a;Ballerini et al, 2009;Regular et al, 2009), despite the importance of identifying tipping points and thresholds when buffering capacity (i.e., both behavioral and demographic) is overcome.…”

There is more to climate than the North Atlantic Oscillation: a new perspective from climate dynamics to explain the variability in population growth rates of a long-lived seabird

“…NAO can explain variation in some different ecological variables in some species, but not in others (e.g. : Saetre et al, 1999;Forchhammer et al, 2002;Durant et al, 2004;Sandvik et al, 2005;Saether et al, 2009;Dippner et al, 2014;Sandvik et al, 2014). These studies and others illustrate the fact that NAO can be highly relevant for some variables and species; but an association may not mean causation.…”

“…where β i represents the slope of the ith environmental covariate X i ; ε, environmental noise, i.e., an independent variable with zero mean and variance σ 2 e ; N t , population size in year t; r, long-term intrinsic population growth rate; σ 2 d , demographic variance; X i,t , environmental covariate i in year t. The parameters β i , r, and σ 2 e were estimated using maximum likelihood (for details, see Saether et al, 2009;Sandvik et al, 2014), while σ 2 d was assumed to be 0.1, which is a realistic value for long-lived birds (Lande et al, 2003). To ensure that the latter assumption did not critically affect the results, different values of σ 2 d were tested; varying σ 2 d tenfold (0.01-1) changed the estimate of β by less than 2%.…”