How are the pen­gu­ins of the South Ork­ney Islands doing?

A recent long-term stu­dy reports on the deve­lo­p­ment of the three brush-tail­ed pen­gu­ins: Adé­lie, Chin­strap and Gen­too pen­gu­ins on the South Ork­ney Islands. The stu­dy com­pa­res their situa­ti­on with the popu­la­ti­on deve­lo­p­ment around the Ant­ar­c­tic Pen­in­su­la. The sci­en­tists can look back on a con­ti­nuous cen­sus data set of 38 years, sin­ce 1978/79. Pre­vious­ly only spo­ra­dic counts were done. While the popu­la­ti­ons of Adé­lie and Gen­too pen­gu­ins were sub­ject to regu­lar fluc­tua­tions, the num­ber of Chin­strap pen­gu­ins decreased ste­adi­ly. Howe­ver, the Adé­lie pen­gu­in colo­nies were also decre­asing. The Gen­too pen­gu­ins did rela­tively well over the years, their num­bers were incre­asing – a trend that is also obser­ved at the Ant­ar­c­tic Pen­in­su­la. The rese­ar­chers explain the obser­ved fluc­tua­tions with a lively exch­an­ge of nes­t­ing birds bet­ween colo­nies of the archi­pe­la­go. At pre­sent, Adé­lie, Chin­strap and Gen­too pen­gu­in popu­la­ti­ons at the South Ork­neys are esti­ma­ted to be about 200,000, 600,000, and 5000-10,000 bree­ding pairs, respec­tively.

Today it is assu­med that a chan­ge in popu­la­ti­on size can be a good indi­ca­tor of chan­ges in the eco­sys­tem. This is rese­ar­ched in a num­ber of krill-eating spe­ci­es, e. g. also the brush-tail­ed pen­gu­ins. The Com­mis­si­on for the con­ser­va­ti­on of Ant­ar­c­tic mari­ne living resour­ces (CCAMLR) uses this data to moni­tor the mari­ne Eco­sys­tem. With that they can set catch limits for the krill and fish fishe­ries.

All three spe­ci­es are bree­ding tog­e­ther on Signy Island, South Ork­ney Islands. While the bree­ding suc­cess of all spe­ci­es is equal­ly good or bad over the years in the obser­ved peri­od, the popu­la­ti­on deve­lo­p­ment is dif­fe­rent. Sin­ce the begin­ning of the con­ti­nuous cen­sus Adé­lie pen­gu­ins decreased by 42% and Chin­strap pen­gu­ins by 68%. In the same peri­od, the ori­gi­nal­ly much smal­ler Gen­too pen­gu­in popu­la­ti­on increased by 255%! His­to­ri­cal data show a com­ple­te­ly dif­fe­rent trend bet­ween 1947 and 1978: the num­bers of the first two spe­ci­es increased enorm­ously during this ear­ly peri­od.

Accor­ding to some sci­en­tists, the popu­la­ti­on deve­lo­p­ment seems to be cor­re­la­ted to the regio­nal decli­ne in sea ice ext­ent and the long-term warm­ing of the regi­on. Howe­ver, the rese­ar­chers of the pre­sent stu­dy are loo­king a bit deeper into the con­text, becau­se ice-loving Adé­lie pen­gu­ins and ice-avo­i­ding chin­strap pen­gu­ins are sub­ject to the same decli­ne. They point out that the sur­vi­val rate of the young pen­gu­ins during their first win­ter, the access to krill stocks and the increase in fur seal num­bers and wha­les as food com­pe­ti­tors in the area, also seem to play a major role. Bet­ween 1977 and 1994, the num­ber of fur seals increased ten­fold at Signy Island.

In order to gain a bet­ter under­stan­ding for the decli­ne of one spe­ci­es and the suc­cess of ano­ther, rese­ar­chers have to look into the dyna­mics of the sys­tem even deeper. Their long-term data of the last deca­des and data from other field of sub­jects are important com­pon­ents for future models and under­stan­ding of the pro­ces­ses obser­ved.