The blue tit family has left the shelter of its nest box at the Wildlife Centre and 8-9 young said goodbye to the camera and left on Saturday 7th June. We wish them well and hope the parents return next year.
Attention now shifts to the sand martins who are busy investigating the holes in the artificial bank built for them last year.
Not so well known or as easily recognised as swallows, house martins or swifts which are all common around the buildings in Montrose, this is an opportunity to get good views of the sand martins from the viewing gallery of the Wildlife Centre.
These birds have flown back from their wintering grounds in West Africa just south of the Sahara and the males have prospected for potential nests near to where they nested last year or within 3kms of their birth site. The female sand martins then come along and see what the males have found or constructed and make their choice.
How they make that choice is a mystery, but they are very gregarious birds and always nest alongside other sand martins in a colony. Research has shown that chick survival is much better in a large colony than for solitary nests.
A factor which may influence the female in choosing a mate is the depth of the nest hole. The chicks have a better chance of surviving if the hole is 70-90cm long, so the female may choose the deepest hole.
When the decision is made, the nest cup is created at the end of the hole using feathers, grass and leaves. The choice of particular plants as a source of nesting materials can help reduce the infestation of mites and bacteria, due to their antiseptic properties.
Once laid, the 4-6 eggs take about 14 days to hatch, during which time both parents take turns in sitting on the eggs to keep them warm. After the eggs have hatched, both parents have a hectic three weeks of catching insects to feed to the helpless young before they can leave the nest and fend for themselves. This is why they choose places near to water where an abundant supply of flying insects can be relied upon at the critical time when the young have to be fed.
Sand martins in Scotland only have one brood (they can have two if they nest further south), so there is plenty of time for both parents and juveniles to feed up in preparation for the long flight to Africa for the winter. The juvenile sand martins may roost in and around their home nest hole for several weeks before making their way gradually south. The parents will leave the nesting colony later but then make longer flights than their offspring and overtake them on the way through France and Spain and over the Mediterranean to West Africa.
The smaller hops of the young sand martins are probably part of the orientation process, so that they can easily find their "home" when they return next March.
Sadly, the "when" in the previous sentence should really be "if", because the survival of both adults and juveniles are dependant on the state of the winter quarters. Severe droughts in the Sahel region of sub-Saharan Africa have caused dramatic reductions in the number of sand martins returning to the UK in some years. Also the loss of suitable natural nest sites restricts the birds ability to recover quickly from the lean years, so artificial nest banks are a great help in conserving this species.
We can follow this activity from the Wildlife Centre where the sand martins can be seen flying with house martins and swallows as they all forage for insects over the ponds.