Where do Shorebirds go to Sleep?
Eating and sleeping – two of my favourite pastimes, and I’m sure many of you would agree! For our shorebirds, eating enough food for survival and resting to make sure energy is conserved are a challenge they must face every day. In our previous blogs we have discussed how different waders have adapted certain features to help them find their prey as easily as possible. As they spend the vast majority of their time feeding, making this process as energy efficient as possible is essential. However the length of time shorebirds can spend feeding heavily depends on two main factors – tidal height and daylight.
At low tide, there is an expanse of space available for them to find a meal – see our previous rocky shore blog for just one example! But what happens at high tide when feeding grounds are covered by the sea?
As the UK experiences two high tides and two low tides per day (known as semidiurnal tides) there is a high chance that at least one of the daily high tides will fall during daylight hours. At this time, birds may try to make the most of the daylight and search for food in areas not covered by the tide. Turnstone and redshank will scavenge for sandfly larvae and other juicy invertebrates living amongst the dry rotting seaweed that has been washed up on the beach. This particular food source is vital for these birds, as they have often been seen preferentially choosing to feed here at low tide, even when other options are available.
Turnstone feeding amongst washed up seaweed at Stag Rock
Smaller waders such as dunlin and sanderling may also attempt to feed along the water’s edge at high tide picking out small marine creatures living close to the sediment surface. However for those birds with longer bills, for example bar-tailed godwit and oystercatcher, which usually feed on worms living in the wet sand and mud, their food source is completely unavailable to them.
When all feeding options are closed to our shorebirds, conserving their energy in essential, and one great way to do this is to gather in large groups and form a high tide roost. Safety does come in numbers and being together in one location with so many eyes to watch out for danger is the best way for our birds to get some rest. Most shorebirds use this technique, with roosts often comprising of a mixture of many different species.
High tide roost at Seaton Point comprising of oystercatcher, bar-tailed godwit, knot, dunlin and redshank
To maximise energy preservation birds will sleep on one leg and tuck their bill into their plumage. This reduces the amount of body parts not covered by warm feathers being exposed to the elements, so they don’t have to use as much energy keeping warm. Large groups of birds can attract predators, with raptors such as peregrine falcons and sparrowhawks always on the lookout for an easy meal, so shorebirds will open their eyes regularly during their sleep to look out for such risks and keep the group safe.
One particular exception to the rule are curlew – their long downward-curved bill makes them experts are searching for worms… not just on mudflats but also in fields too! Earthworms make up a significant part of a curlew’s diet, and can more often than not be seen foraging in fields close to coastal areas that are lacking in access to mudflats.
High tide also gives birds the perfect opportunity to have a good wash. Caring for their feathers is an important part of their day and can be quite a lengthy process. Ideally birds would prefer to bathe in fresh water, which is one of the reasons river and burn mouths are a popular location for a high tide roost, for example Alnmouth and Long Nanny Burn. Following bathing, birds then take time to preen their feathers; a process which makes sure their feathers are waterproof and free from parasites.
Turnstone and purple sandpiper preening during a high tide roost
When the tide is in, the choice of locations for feeding and roosting is limited. At this time, our shorebirds are particularly vulnerable to disturbance as they have nowhere else to go. Birds on instinct will fly away from potential threats, be that predators, dogs or even people walking along the beach. Repeated disturbance causes the birds to use up large amounts of their precious energy, and with feeding grounds covered and no way to quickly replenish their reserves, their chances of survival are significantly reduced. Research has suggested that only 10 disturbance events per day is enough to cause shorebirds to be pushed into an energy deficit – meaning they use up more energy by flying away than they can replace during the rest of that daily tidal cycle (Lilleyman et al, 2016). With most disturbance likely to occur at high tide, this statistic highlights just how important these roosts are for our shorebirds.
With meteorological spring upon us, shorebirds are starting to think about making the long journey to their breeding grounds, with some travelling as far as the high Arctic! As you can imagine, flying such a long way is an energy-consuming task! To give our shorebirds a fighting chance of completing their migration in one piece, it is essential that they can feed and rest on our shores with as little disturbance as possible. Please look out for the birds, especially at high tide. Giving birds a wide berth (40 or 50m if possible) by walking around them will prevent them from flying away and landing in a less suitable location.
Redshank, turnstone and knot feeding on a washed up wrack of seaweed
As the tide recedes, a fresh supply of food becomes available to our shorebirds. They disperse and return to the rocky shore or mudflats to feast, well rested after their high tide snooze.
Source: Lilleyman, Amanda & Franklin, Donald & Szabo, Judit & Lawes, Michael. (2016). Behavioural responses of migratory shorebirds to disturbance at a high-tide roost. Emu. 116. 10.1071/MU14070.
