Why Build Nests?

Of course, Ospreys can build their own nests but while they are rare, and still missing from much of their ancestral range, active management is beneficial to the species. All the above actions have been used to assist with the restoration of depleted Osprey breeding populations and to increase breeding success in North America and Europe, including Scotland.

Pairs breeding in built or rebuilt nests have been shown to be more successful than natural nests. This is particularly the case with first time breeding pairs building their own nest. It is important to bear in mind that in ancient times before human persecution most young ospreys would have bred in long established and secure eyries. In the British Isles, with an increasing osprey population, we are in the process of restoring the suite of established eyries.

The aim is to increase the breeding population of ospreys in the British Isles and to restore it to its previous range where practical. A larger geographical spread of the species will enhance the Ospreys long term chances of survival.

Ospreys are very slow to recolonise lost range.

Ospreys have a very slow ability to recover lost range throughout the world. This was most noticeable in North America where recovery from the pesticide crash of the 1950s/1960s was very slow. Conservationists overcame this by translocating and hacking young and by building artificial nests. In Scotland, the recovery has also been very slow with an average natural spread of about four kilometres per year. Although this has changed in recent years following the translocation project at Rutland Water in central England.

This slow recovery is due to various factors. Ospreys prefer to breed near other ospreys as they are semi-colonial, they fish at common feeding sites and they are usually faithful to their eyrie and their mate. Males have a strong natal philopatry with females being more spread . Yound adult ospreys prefer to take over an established eyrie in a ‘colony’ or build nearby, rather than build a new eyrie in a new locality. Ideally they prefer to find an experienced breeding bird with an established nest which has lost its previous year’s mate.

Of course, pioneering pairs do establish in new localities, rarely more than 50 kilometres from the present breeding range. Experience has shown that it is important they are joined by other pairs within a period of several years to create a new colony, other wise the colonisation attempt may fail. The growth of each new colony is slow at the outset, but if successful it becomes rapid and then levels out. In some case it may even decrease.

Nowadays, despite these old established colonies being full, there is still much competition by young potential breeders (known as intruders) trying to join these colonies. Research on colour-ringed breeding adults in Northern Scotland over many years has shown that annual survival is 91%. This means that on average in a ‘colony’ of 10 pairs of ospreys there is only a requirement for two new replacements per annum, yet we record many intruders at nests within these areas. Intruders often visit nests containing pairs throughout the nesting season. Sometimes these visits can be surprisingly aggressive and can result in broken eggs or even the eviction of the resident female. There have been reports in the past of birds actually been killed during these fights.

What is clear is that many ospreys do not breed when capable of breeding. They are waiting until older to find a place in an established colony, usually due to the death or non return of an older bird. Each delayed season for an individual means a 9% chance of dying before the next breeding attempt. So a bird failing to establish itself until its fourth, fifth, sixth or seventh year has a greater chance of death before breeding successfully, an additional 9%, 18%, 27% or 34% chance of dying.

In these circumstances, it is good management practice to try to encourage ospreys to breed in new regions of the British Isles by the provision of secure eyries. This is particularly true now that the first translocation projects have taken place. The Rutland Water Translocation Project carried out in 1996 – 2001 by Rutland Water Nature Reserve, Anglia Water plc and the Highland Foundation for Wildlife created a small breeding population in Central England. It also resulted in two translocated males, from the Scottish Highlands and released at Rutland Water, establishing themselves in Wales, and attracting passing females to breed in 2004. One pair reared one young – first for Wales for several hundred years; the other pair lost their nest in a storm and the two young died. This nest was rebuilt in the winter and this pair continues to breed in north Wales.

The Rutland Water Translocation Project and the natural colonisation in the Lake District have changed the ‘map’ of the British Isles for Ospreys – so nest building now offers greater chances of success throughout the country. This document outlines the most effective and up to date methods.

Early Nest Building Activities.

In 1960, I built my first artificial nest in Scotland using an old cartwheel at an old nest which had been vandalised. It was never used which was not surprising, in hindsight, because I did not add any nest material. In the last forty years, osprey workers throughout Scotland became much more involved in osprey nest management as the population increased. First of all by repairing nests which had become damaged by storms and then providing new nests.

Ospreys can waste valuable time early in the season attempting to rebuild damaged nests, especially when a main supporting branch has broken. This can result in nesting failures and even to the break up of pairs. The work has proved to be successful as elsewhere in the world. As the years have gone by we have changed to trying to make our built nests look as natural as possible for aesthetic reasons.

The following table shows the details for presently and recently used Osprey nests in the Scottish Highlands. 30% of used nests were built by us and 15% were rebuilt by us after the destruction of a natural nest through weather or tree failure. Similar information is known for other regions.

Details of Osprey Nests in the Scottish Highlands.

Data from Roy Dennis & Colin Crooke (Highland Foundation for Wildlife and RSPB)

Choice of Locality.

The key requirements are:

There are four different types of localities which are suitable for building osprey nests:

Is important to assess the suitability of an area for breeding ospreys before a programme of nest building is started. Nowadays, anywhere in the British Isles is possible but there will be far more chance of success if the area has a variety of good fishing habitats and available fish species. Rivers, large streams, lakes, lochs, large ponds, gravel pits, estuaries and shallow coastline will all provide opportunities for ospreys to fish. A mixture of these habitats is most advantageous.

Generally speaking the higher the number of species of fish the greater the opportunities for ospreys to hunt and there are real advantages for those which can exploit estuarine species such as grey mullet and flounder. A wide variety of coarse species in freshwater sites are also important. Salmon are not taken as they are too small when they go to sea and too big when they return to the rivers.

The best place to start a project is in those areas were ospreys are regularly seen and especially those where they linger or spend part of the summer. Remember that sub-adults, especially two-year olds, often summer to the south of the breeding range.

Once a suitable area has been located it is necessary to find three to six potential nest sites within a radius of five to ten kilometres of the best fishing sites. Nests are most likely be used in new areas if they are visible to ospreys from regular fishing sites or enroute between good fishing sites. Remember ospreys see the nests from the air and have remarkable ability to locate nests.

Ospreys are becoming more tolerant of humans. Chicks that fledge from nests in view of people are more able to nest in locations close to humans. Ospreys in remote nests are very sensitive to disturbance and will fly up at distances up to and over 500 metres, while pairs breeding in public places will not even get off the nest at 100 metres. This is now the case in Scotland and is frequent in other countries, especially where they were never persecuted.

Nevertheless, it is better to build nests at least 200 metres, preferably further, away from the nearest habitation or public place and it is best to avoid areas of intense human use. In the best areas for ospreys, nests and platforms should be placed at least 200 metres apart.

Choice of Nest Site.

There are three types of artificial nest sites and each is described below:

a. nests built in prominent trees to resemble natural nests.

b. nests built on poles specially constructed for ospreys.

c. nests structures built on pylons, towers and other man made structures.

Select a prominent tree. Osprey eyries, being large and on the crown of prominent trees, are very visible structures to other ospreys and their behaviour suggests that young ospreys look for eyries to occupy. The tree should be easily seen by passing ospreys and should be in the sort of place an osprey would choose to perch if it had a fish. If the loch or lake is secluded then a prominent tree on an island or close to the shore could be chosen. Normally one is looking for a tree half a mile or more back from the water’s edge out of usual public use.

Finding the best tree can take days of searching, while building the nest may take only three hours. Take plenty of time to find the best site, try to think like an osprey. If you put up a nest in a poor site the chances are it will never be used even in good osprey country.

Scottish ospreys nest in trees ranging in height from 12 feet to 120 feet - the important feature is that the tree is prominent to its neighbours or is in a prominent clump of trees. It is an advantage to have at least one dead tree or dead trees, or dead-topped trees close to the nest to serve as perches for off-duty birds, and for them to collect nest material in flight. It is probably best to choose a tall conifer (Scots pine or Douglas fir are good) or use a safe dead tree. Deciduous trees can be used but the general shape is often not as easy to convert into a nest site, than tall slender shaped trees like conifers.

In many areas most trees are not suitable for ospreys for nesting. They prefer tall trees which have been damaged and have broken tops caused by storms, heavy snow, or lightning strikes. These provide a secure base for their nests.

To build a new nest, at least three people are needed including a good tree climber. Use an extending ladder, climbing ropes, nylon slings, karabiners, bushman saw, axe, hammer and nails, flexible wire, courlene twine, plastic sacks and a good knife.

One person climbs tree and secures himself near the top with climbing slings just below the top most branches. He also secures a karabiner and a small pulley on a convenient branch and runs a long climbing rope to the ground. The rope is joined so that a continuous loop passes from the base of the tree up through the pulley; this is for the ground party to pull nest material up to the climber. Sometimes, the climber needs to remove some side branches as he climbs the tree to allow the stick bundles to be pulled up the tree.

The first task is to cut off the top of the tree at the first ring of strong side branches, while colleagues on the ground select nest materials. First of all three or four strong branches about 5" thick and 5-6 feet in length - these can be live or dead as long as they are strong. Next bundles of dead sticks up to 2" thick and 2-5 feet in length (preferably barkless conifer sticks which have weathered and have a pale look - this is to make the nest pale and obvious to passing ospreys). These should be tied in bundles about a foot thick with nylon slings which can be hitched and unhitched easily from the karabiner on the endless rope. At least about four to six bundles are needed. These must be dead sticks not cut live.

The next step is to fit the long branches into the fork in a triangle (or square shape) to form the main support. Nail or tie into main branches and the top of the cut off trunk. Secondary supports are tied or nailed across the main frame. The ground party then pull up bundles of sticks starting with the biggest. The climber builds these into a circle at least 4 feet in diameter. The lower ones are tied by twine or soft wire to the base. They should be worked together and some sticks are laid across the middle as well. Keep building up until the nest is at two feet high - it must look big and bulky.

When you’re getting towards the finish, at least two sackfuls of nest lining is pulled up. This should be a mix of dead grass, moss and leaf litter or rotted straw. This must be pushed deep into the base of the nest, really pushing it into the sticks. When the nest is full of dead grass and leaf litter it should be flat. Then take one more bundle of dead sticks, the whitest possible, at least an inch thick but not as long as the ones in the base in the next and these are arranged around the edge of the nest. Some should pushed at an angle down through the lining to hold the whole thing together. Then spread one more load of earth or leaf litter to form a nest which looks as though it has been home to a brood of young ospreys. Finally, some people have white washed the outer ring of sticks to make the nest obvious from the air, but pale sticks and dead grass will do.

The last important action is to create an extremely good perch for ospreys preferably close to the nest. If possible leave one of the top branches sticking out from the side of the nest as a perch - in fact it is good to leave a perch beside or just above and to one side of nest. Remove foliage from this branch. Trim a nearby tall tree, or select a dead tree, to act as an off duty perch. If necessary cut and clean a prominent branch at the top of the nearest tall tree to create a really good perch. The final nest should look as though it has been made by ospreys.

In areas where there are no suitable trees for building a natural looking nest, it is possible to use nesting poles. These have been used in various parts the world to good advantage and the best examples pairs in this country are at Rutland Water nature reserve. Many designs have been used in North America.

First, you need a strong pole, about 30 feet or more in length. The best are those used by electricity companies for local supply lines. Sometimes, it’s possible to beg or buy a few when they are replacing poles. These are very strong poles and very well treated. Next, you need to construct a square wooden platform to fit on the pole to hold a nest. Use 6" x 2" treated timber to make wooden frame of 1 to 1.25 metre square. The four inner spars are jointed to form a hole which fits the top of the pole. The outside frame is made of similar timber and the whole frame is covered with wire mesh. Wooden or metal pins are inserted in the outer frame to hold the nest from falling. The whole frame is bolted to the top of the pole with bolts. It is also possible to use a metal basket specially made to fit the top of the pole to hold the nest, instead of a wooden frame.

The nest pole is erected in a suitable area for breeding ospreys. It is embedded at least six feet into the ground using an excavator; the nest platform should be at least 24 feet above the ground. A successful system abroad is to site poles in areas to be flooded before flooding or as at Rutland Water to erect them when reservoirs are at very low water levels. Once the nest pole is secure, a nest similar to that described above should be built on top of the frame and tied into the structure. This can best be done by using a safe ladder which is tied to the top of platform. Try to build the nest as big as possible. Finally, fit a tall perch which is nailed to the pole and up against the edge of the platform. It provides a T-shaped perch which is several feet above and to the side of the nest.

c. Artificial structure.

Ospreys regularly nest on the top of electricity pylons in various parts of the world, for example Germany, Australia and North America. There are at least four in Scotland. Sometimes these nests cause problems for the electricity companies and special metal baskets have been designed by the electricity companies in other countries, for ospreys and white storks. These are be bolted on top of the pylons to keep the nest clear of the important parts of the electricity supply. These can be very successful nests as they are secure from human interference. It may be possible to find companies which might be pleased to help with a conservation project for ospreys. At this height and in these circumstances, it will not be possible to build a big nest, but at least some nesting material should be placed in the basket to encourage nesting.

Nesting platforms of a similar style to the pole or the pylon can be fitted on the top of channel markers, navigation towers or structures in coastal and estuarine areas. But make certain you have permission. There are other potential sites. At least one pair has tried to nest on mobile phone mast in Scotland and another nested on the chimney stack of a deserted house.

Maintenance

Once built it is important to maintain nests in good condition. They should be inspected in March to repair any winter damage. Remember that they may not be used for many years but it really is worth keeping them in good condition, just in case. Do not give up hope. This year, for example, I was told by a friend in the Forestry Commission that a nest I built in a Scots pine in Sutherland in 1993 was finally used in 2004 – a wait of eleven years!

In some areas, especially in lowland England, osprey nests built close to water may be used for nesting by Canada geese. If they do, they are capable of deterring ospreys from nesting; especially as they may have settled in the nest before ospreys have returned in early April. In Canada, they suggest using the convex lid of a dustbin to cover the nest during the winter and leave it in place until the first ospreys are seen in April. The smooth surface will prevent Canada geese from nesting earlier.

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Conclusion.

It is important to realise that many artificial nests may never be used but at least it’s worth trying to encourage ospreys to return to their original range throughout the British Isles. It’s incredibly exciting when your first nest is used and there has never been a better time to try. With the new outlying pairs at Rutland Water and in Wales, as well as hopefully some further translocation projects, the future for this wonderful bird looks very good.

If you have any queries, please give a call or write. I would be interested to hear of any successes or improved techniques.

Best of luck

Roy Dennis

PS: Consultantancy. If you decide that you are not able to do this work yourself but require help to select and build ospreys nests, we are able to provide an expert consultancy service to carry out such work.