Black-billed gull colony update February 2019

The gulls have finally left the Ashley/Rakahuri River after more than 3 ultimately successful months. They first attempted nesting just below State Highway 1 in mid-November, got washed out on 26 November, and were already building new nests 5km upstream by 1 December. This was after an earlier attempt to nest on the Waimakariri riverbed had been foiled by floods.

When the birds had moved far enough away from the nesting area to avoid disturbance, a count was made of nests by members of the ARRG. This was quite difficult to do as in several places there were as many as 6 per square metre. A total of 768 nests were counted, not all of these would have been used. A total of 22 dead chicks were seen in the nesting and creche areas – presumably this was due to natural causes.

The first chicks had hatched by 30 December and they soon moved off the nest area to a creche at the river’s edge 50m to the north. Chicks are hard to count, but efforts in late January and early February resulted in totals of 500 and 450. By 5 February all the gulls had moved to a new creche site 300m to the west. By this stage, most of the chicks had fledged and would have flown there. However, there were several that couldn’t fly, these were presumably herded there by their parents. At this site the adults continued to feed the chicks.

Piles of feathers along the river banks and in vegetated areas near the nest and creche areas show the effects of predation. It seems that approximately 25 chicks were taken by harriers, this is quite natural.  However, 9 appear to have been killed by ground predators – perhaps feral cats or ferrets. This is despite ARRG having permanent traps either side of the river and putting several temporary traps near the colony. About 9 were also killed by a reckless four-wheel drive operator.

The last fledgling flew away on 19 February, just as the river had almost completely dried out in this area. Soon afterwards perhaps several hundred fledglings and adults were spotted feeding in an irrigated paddock just south of the river.

It seems that in excess of 400 chicks were raised – probably a good outcome given that this was the third nesting attempt made by the colony. With 768 nests and 400 chicks fledging, a productivity of 0.52 was achieved.  Unnecessary deaths of chicks were minimized by ARRG trapping and by blocking of access to the river by ECan and ARRG. ECan rangers were also very proactive in trying to prevent interference with the colony. In future nesting seasons we will be continuing to try to keep traffic out of the riverbed and we are working on extending our trapping network. Rare native birds should never be killed by reckless people driving through signposted nesting areas. These signs should not be deliberately vandalised as has commonly happened.

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