1. Projet Title: Restoring Breeding Ospreys in the Upper St.
Lawrence River -
A Case Study
2. Contacts
Peter J. Ewins
Conservation Strategies Division, Environmental Conservation Branch,
Environment Canada - Ontario Region,
25 St. Clair Ave. East (3rd floor), Toronto, Ontario, M4T IM2.
Tel.: (416) 973-6000; FAX: (416) 973-5665
John Mackenzie
Ontario Ministry of Natural Resources,
P.O. Box 605, Oxford Avenue, Brockville, Ontario, K6V 5Y8.
Tel.: (613) 342-8524; FAX:(613) 342-7544
Bud Andress
St. Lawrence Islands National Park, #2 County Road 5,
Mallorytown Landing, Ontario,KOE 1RO.
Tel.: (613) 923-5261; FAX:(613) 923-2229
3. Agencies Involved
Canadian Wildlife Service, Environment Canada
Canadian Parks Service
Ontario Ministry of Natural Resources
Ontario Hydro
Kingston Field Naturalists
Cardinal Fish and Game Club
Muttart Building Supplies
4. Restoration Goals
To provide suitable nest structures for Ospreys in areas where natural nest sites are scarce. To increase public awareness of the shortage of natural nest sites, and the need for conservation action.
5. Project Type
Construction and installation of wooden nesting platforms mounted on old hydro poles at small rocky islands adjacent to suitable fishing areas.
6. Background and Rationale
Ospreys (Pandion haliaetus) are majestic, large birds of prey (raptors), which eat fish up to about 30 cm long. They catch fish mostly in shallow water (up to 2 m deep) by diving with wings closed from heights of up to 20 m or so. Most Ospreys which breed in Canada and the United States winter in South or Central America. They build large stick nests in exposed sites, preferably over or close to water. In this way, they reduce the risks of egg predation from raccoons, and they get sufficient aerial manoeuvrability when approaching or leaving the nest (Poole 1989). In the Great Lakes, the clutch of 3 eggs is laid in late April, and the chicks usually fledge by early August.
Before European settlement of the Great Lakes, Ospreys probably bred commonly around most shorelines close to productive river systems and other shallow water areas. Their nests would have been built at the very top of large trees, live or dead, which had sufficient side branches to provide firm support for the heavy nest. Today, the shorelines of the upper St. Lawrence River, like many around the Great lakes, have been developed for human habitation and recreational activities. As a result, there are now very few suitable natural nest sites there for Ospreys. A few pairs have attempted to nest in snags in beaver swamps, or in live white pines further from the river, but the nests often fall down on these smaller trees, and raccoons can readily climb trees on dry land, and will swim out to snags too (Ewins 1994).
Osprey populations in the Great Lakes, as in many other breeding areas, have been increasing steadily since the 1970s, when DDT and other toxic organochlorine pesticides were withdrawn from use (Poole 1989; Ewins et al. 1995). Although it is well known that DDT causes eggshell thinning in many bird species, it is still widely used in Latin America. Our preliminary surveys indicated that the upper St. Lawrence River offered suitable fishing areas for Ospreys, but probably a shortage of safe, suitable nest sites close to the fiver. In other parts of the Great Lakes and North America, Ospreys regularly build their nests on hydro poles and other types of artificial nest-structure (Ewins 1995; Ewins et al. 1995). So, a cooperative project was launched in the fall of 1992 to install 5 artificial nesting platforms on suitable small, rocky islands in the Upper St. Lawrence River.
7. Regulatory Considerations
a) Ontario Ministry of Natural Resources permit required for egg collecting/chick sampling.
b) Canadian Wildlife Service permit required for banding birds.
c) Landowner permission is required for platform installation.
8. Criteria
The extent of suitable shallow water foraging areas (less than 2 m deep) was assessed from hydrographic charts, and speaking to locals who had seen Ospreys fishing in various stretches of the river.
An aerial survey of the general area, including the archipelago of islands within the river itself, was conducted between Kingston and Mallorytown. This survey identified at least 40 potentially suitable sites for a platform. Most of these potential nesting sites were small (less than 1-2 ha) rocky islands lacking tree cover. All were uninhabited. All platforms were later placed at exposed, treeless parts of each island, at least 300 m away from the nearest cottage. A few pairs of Ospreys were known to breed within 20 km of these areas. Experience elsewhere has found that the chances of platform occupation within a few years are much higher when birds are already nesting in the general area.
Local resource agency staff (OMNR, Canadian Parks Service) identified landowners for sites targeted, and sought support for the project. At least 6 landowners were keen on the idea of having an Osprey nesting platform on their property.
Once all this had been done, 5 sites were selected between Mallorytown
and Rockport. Sites
were at least 2 km apart, so reducing the chance of intra-specific
/ territorial interference from adjacent pairs.
Inventories of breeding colonial fish-eating birds were checked to ensure that no Osprey platform was installed on an island used by breeding Common Terns or other sensitive fish-eating birds, which might be forced to vacate the site if breeding Ospreys moved in.
9. Project Design
Details of the various design and construction options for artificial nest platforms for Ospreys are provided in a published manual on Osprey platforms (Ewins 1994). The basic design used in the St. Lawrence River was a rock-mounted shortened hydro pole with a modified industrial pallet mounted on top. Coordination of a number of partners on the ground ensured that the installation process went smoothly.
Although this kind of platform has been successfully installed in other areas in mid-winter, unpredictable ice conditions in the St. Lawrence River made access over ice dangerous, so the work was done using boats before freeze-up in the fall of 1992.
10. Implementation
An old hydro pole, usually cut to 8-10 m, with a 1m ¥ m skid/industrial pallet mounted on top of the pole, using side walls and support braces was used. The cast iron rock mounts were first bolted deep into the bedrock, then the whole structure was raised upright using a block and tackle. Three galvanised guy wires provide valuable additional support in other areas, but were not used in this case. Anti-predator guards (sheet metal nailed carefully around the base of the pole) were not installed on these poles, but will be added before the 1995 breeding season. The basic pole and platform design was as shown in Figure 1, minus the guy wires and predator guard. Also, the platform base was wooden slats on the pallet, not a wire grid. Either design will do though.
In the fall of 1993, 5 platforms of this type were installed on small islands in Canadian waters of the St. Lawrence River between Mallorytown and Rockport.
11. Degree of Environmental Intervention
This work had minimal impact on the physical structure of islands used. Although poles and wood treated with chemical preservatives will last longer, in some smaller, more sensitive water bodies it may be preferable to use cedar and untreated poles. Although no study was carried out to investigate changes in other biota using these islands, it is likely that some limited changes would occur. These include some enrichment of the ground beneath the nest, from faeces and pieces of dropped fish, and desertion of the island by any breeding animals which could not tolerate such close proximity to a nesting raptor. However, many species are thought to gain increased protection from ground predators when nesting close to a large bird like this.
12. Cost
Some staff/volunteer costs were donated by individuals and partner organisations involved with the project. These items are listed below as "Free ". The poles and rock mounts would have been by far the most expensive items if they were bought new. However, used ones can often be found from local offices of public utilities, once they are approached as potential partners. Approximate costs (for 5 platforms) were as follows:
Installation
Poles, support braces, and rock mounts: Free
Pallets and support timbers: Free
Assorted timber, nails and hardware: $30
Chicken wire for platform base: $30
Rental of jack hammer: $300
Bits for jack hammer: $150
Purchase of insulated waders: $100
Incidental safety equipment: $100
Transportation for work crews (boats): Free
Boat fuel: $150
Boom barge and tow boat use (incl. fuel): Free
Video film and photo equipment: $250
Total cost (for 5 platforms) ca. $1 110
Annual monitoring and maintenance:
Usually these sites can be checked for occupation during the course
of other work, so no specific
additional costs for staff time are incurred. Average annual maintenance
costs after the platforms are about 5 years old are estimated
to be about $10 per platform (to cover replacement side walls,
and possibly guy wires if poles start to lean). It is expected
that soundly built platforms would need maintenance only every
5-10 years or so.
13. Biological Assessment
Since 1993 all sites have been checked at least twice annually. A visit in mid-May determines whether the site is occupied (usually by seeing a bird incubating or standing at the side of the nest). A second visit in early to mid-July counts the number of large young produced, to allow calculation of mean reproductive success for the area. At these St. Lawrence River nests prey remains and a small blood sample from chicks were also collected ( for analysis of organochlorine contaminant levels). All chicks have been banded, to enable biologists to assess whether birds are surviving to recruit back into the local breeding population (Ospreys usually first breed when 3-5 years old). Annual checks of this kind are recommended to monitor the health of the local Osprey population. From the prey remains ( fish bones), we have confirmed for this breeding area that shallow, warm-water species of fish form the bulk of the diet - mostly suckers, bullheads, yellow perch, pike and centrarchids (sunfish, pumpkinseed, rock bass etc.).
14. Measures of Success
In 1993, the first season after installation, 3 of the 5 platforms were occupied, and all were successful, producing an impressive total of 8 large young by mid-July (average production of 2.7 young per occupied nest).
In 1994, all 5 platforms were occupied, and 4 produced large chicks by mid-July (at 4 of the accessible platforms, 6 large young were produced, i.e. 1.5 young per occupied nest on average). One nest failed in 1994 - the remains of broken eggs in the nest and fresh claw marks up the pole implied raccoon predation. This rapid rate of occupation exceeded eveyones expectations. In other areas it may take 4-5 years or more for platforms to become occupied, especially where Ospreys are not nesting already in the immediate vicinity.
Generally, if an Osprey population is producing a mean of 0.8 young per occupied nest per annum, then it is thought likely to be able to maintain itself.
The local press attended some of the platform installations, and the articles which resulted were well received, and a fitting recognition of the efforts of all partners. The occupation of all 5 platforms within 2 years was a wonderful achievement, and many cottagers and boaters along this stretch of the St. Lawrence River now enjoy the thrilling spectacle of fishing and nesting Ospreys from April through August each year.
Success Rating: 4
15. Key References
Ewins, P.J. 1995. Artificial nesting platforms for Ospreys: a construction manual. Environment Canada: Toronto (in press).
Ewins, P.J. 1995. The use of artificial nest sites by an increasing population of Ospreys in the Canadian Great Lakes basin. J. Raptor Res. (in press).
Ewins, P.J., Postupalsky, S., Weise, T. and Addison, E.M. 1995. Changes in the status, distribution and biology of Ospreys (Pandion haliaetus) breeding on Lake Huron. J. Aquat.Ecosystem Health (in press).
Poole, A.F. 1989. Ospreys. Cambridge University Press, Cambridge, U.K.
Correct citation for this contribution:
Ewins, P.J., Mackenzie, J., and Andress, B. 1995. Restoring breeding ospreys in the upper St. Lawrence river - A case study, p. 99-105. In J.R.M. Kelso and J.H. Hartig [editors]. Methods of modifying habitat to benefit the Great Lakes ecosystem. CISTI (Can. Inst. Sci. Tech. Inf.) Occas. Pap. No. 1.