Shorebirds including Bar-tailed godwits only forage when the mudflats are exposed with low tide. The tidal rhythm is caused by the combined gravitational forces of the moon and the sun and by the rotation of the earth, a simple fact. However, between places the amplitudes and the timing of the low and high tides differ dramatically, influenced by complex interactions between the position of land and large scale oceanic currents. In Barr Al Hikman the mudflats are exposed almost twice per day (in fact, twice per lunar day on average 12 hours and 44 minutes), with very high and low spring tides around new and full moon (approximately 3 to 0. 5 m). But in between, the tidal height differs enormously between high and low tides. With some low tides there is more water than with some high tides.
Scientist can predict the tides with advanced computer models. But for humans it is very difficult to know by heart when and how high the next tide will be. When we are in the field we keep on checking the tidal information. Shorebirds do not have such information at hand, but their whereabouts completely depend on the tidal rhythm. Can our Bar-tailed godwits predict the tide that is ahead? We don’t know yet. Many organisms have internal clocks. Also organism that live in the intertidal area are known to have internal clocks which help them make decisions on when to forage. We know very little about how Bar-tailed godwits decides it is time to forage. Perhaps the transmitter birds can give us some information.
Above video is inpired on the tidal rythm of Barr Al Hikman. The rythm is related to the timing of the lows and highs and the melody relates to the amplitude of the highs and lows. Music and video by Maaike Ebbinge