The 2022 breeding season proved to be a challenging one for kororā on the West Coast.
Our monitored sites at Charleston had a late start to the breeding season, with the first eggs laid in late August, two to three weeks later than normal. From then on kororā bred in a slow trickle, with eggs still being laid in late October. Sadly, over half of these eggs did not reach hatching after being abandoned by the adults.
Lack of easily available food is the likely cause of this poor breeding season, with the adults having to take long foraging trips at sea whilst the other parent stayed on the eggs. If the changeover time is too long then the adult on the eggs will have to abandon the eggs in order to feed themselves. This meant we had a low rate of breeding success, with only 35% of eggs successfully fledging in one colony and 45% in the other. This is comparable to some previous poor seasons such as 2016 and 2017 (37% & 43%), but significantly lower than the last two seasons (80-90%).
Kororā lay two eggs and two chicks will fledge in good years – two chicks fledged from two eggs would be 100% breeding success. We also record chicks per nest, and this year, over the 27 monitored breeding burrows, the average was less than one chick fledged per nest.
|Site||Breeding burrows||Breeding attempts||Eggs laid||Chicks hatched||Chicks Fledged||Chicks per breeding attempt||Breeding Success||Failed attempts|
Although the number of eggs laid at the Nile colony were higher than last year, this number was inflated by the discovery of three additional breeding burrows (which were likely to be breeding in previous seasons). Additionally, and somewhat interestingly, two pairs laid a second clutch of eggs this season. This is common at East Coast colonies, but quite a rarity on the West Coast. One of these pairs successfully raised their first clutch and the second clutch failed, whilst the other failed on their first clutch before successfully raising their second clutch. We assume it was the same pair each time but will be able to use data gained from microchips or PIT tags in the future to confirm this.
At the Rahui colony, one burrow was used for two breeding attempts and in this case it was for different birds. The first attempt failed with unknown birds, and the second attempt with the nest box’s usual occupants (identified using the PIT tags and reader) was successful.
Our rangers noted that this was the third warm water season in a row and the birds struggled for food. Experienced breeders may have had more success and resilience. No adult (breeding bird) deaths were recorded in these two colonies, which bodes well for the 2023 season when waters should be a little more traditional after the shift from La Niña to El Niño conditions occurs.
Our Masters student, Luisa Salis-Soglio, has begun to look at the factors that may be contributing to poor breeding seasons, including water temperature and nutrients. We will develop our understanding of the marine factors that could impact breeding success and provide updates on our website.
In addition to our two fortnightly monitored colonies, there are several other colonies scattered up and down the Buller coastline that are visited by our ranger once or twice a breeding season. These colonies range in size from 1-2 breeding pairs up to around 20 breeding pairs. Although not as intensively monitored as our two key sites, our visits still provide us with valuable insight into population trends at these sites and add to a long-term data set to help improve understanding of blue penguin/ kororā on the West Coast. These colonies generally had similar numbers of breeding pairs to last season, although as was the case at the Nile and Rahui colonies, breeding success was likely lower than last year.
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Read more about our annual kororā monitoring project here.