Seychelles Sooty Terns in trouble again?

After a breeding season in 2014 that was interrupted by a period of extreme food shortage, leading to incubation shifts of nesting birds to stretch up to 13 days without being relieved by their mates, accompanied by desertion of both eggs and young chicks, Bird Island’s Sooty Tern colony has been struck by food shortage again in 2015. Christine Larose and I have again recorded long incubation shifts, and low egg weight, desertion of eggs and starvation of young chicks have again featured prominently.

In 2014 we were tracking Sooty Terns by fitting small GPS loggers to adults during incubation. The GPS study confirmed another suspicion that Chris had had since 2008, relating to the direction that Sooty Terns fly away from the colony in the mornings and from which they return in the evenings. In what he had considered to be the “normal “years, which up to 2007 had been most years, birds flew in the mornings southwards from their nesting area at the north of the island. This direction took them past the hotel on the west coast, as did their evening return. In 2008, however, these flight lines did not materialise, indicating that the birds flew off in some other direction. In 2008 we recorded the duration of incubation shifts and these proved to be much longer than “normal”. From 2009 to 2011 these flightlines again were not apparent from the hotel and in 2011 breeding started late. Following two years of southerly flightlines in 2012 and 2013, the 2014 breeding season began with spectacular flights past the hotel. As incubation progressed, however, these movements ceased and our observations in the colony showed all the signs of severe food shortage. When food was abundant at the start of the season GPS tracks revealed that the birds were indeed flying south and feeding over the shallow waters of the Seychelles Bank, mainly within about 120 km of the colony. As the food shortage progressed and incubation shifts lengthened the Sooty Terns fed further afield and travelled north and west over the deep water. One individual travelled westwards and fed about 900 km from the colony, about half way to the African coast, before returning to the colony after a 6-day absence. Another individual flew north, then east, then south before back-tracking to the north-east, where it found food. It returned to the colony after a 6-day round trip of over 2700 km!

The signs were not good at the beginning of the 2015 season, with few Sooty Terns flying past the hotel. Egg laying normally starts in early June but in 2015 the number of birds flying over the colony area was still relatively small at this time. Intensive laying did not begin until 22 June and even then the build-up of nesting was slow, with most birds not laying eggs until early July. Just before hatching was due to begin Christine and I marked out squares in the colony, in which we counted all the eggs (Sooty Terns nest on the ground). Christine will return to count the chicks in these squares before young birds begin to fledge. So watch this space for news of overall success of the colony in this apparently poor year.

 

P1060812
Incubating Sooty Terns on Bird Island in 2015
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s