Today the colony has been visited on the ground and 34 nests have been counted and labelled with conspicious numbered tags. Those tags help us to discover dynamics in the colony which in case of new nests is welcomed while disappearing nests would be an indication of problems (fe predator activities) triggering case specific action on our side. Trailcameras are installed to record colony activities without any interference or disturbance. Those are also very useful to identify ringed birds and delivered food items.
How and why do we estimate Gull-billed Tern numbers at different times of the day?
During the current stage of the breeding cycle Gull-billed Terns are being counted from distance several times a day in order to estimate maximum and minimum numbers. Both parameters are helping us to understand what is happening in the colony at a certain point in time as they allow to draw different conclusions. The minimum number is telling us how many active nests might be out there while the maximum number is an approximation of the total size of the breeding population. On most days at this early stage of the season there is a significant divergence between those numbers because not all individuals present are actually breeders. Currently 33 pairs (± 1) are breeding, engaging 66 adults, while the maximum number of Gull-billed Terns is 84. Hence we have reason to hope for some more breeding pairs starting later.
The maximum number is usually estimated at evening counts when all breeding birds are back in the colony and non-breeders like to find their night-roosts in the vicinity. Quite the contrary, minimum numbers unfold somewhere around the middle of the day and at low tides when only incubating birds are present and all others are feeding.
Now breeding starts! From the distance we can see 33 active nests. Unfortunately the terns finally decided to establish the colony at a place that has not been fenced in before. In early May we put out 2 fences with a total of 3,4 hectars, but they didn't embrace our offer. Nonetheless, we will fence this area as well, but will wait until some more of the yet undecided pairs have laid their eggs.