Ospreys on Colonel by Lake; an Update

Ospreys on Colonel By Lake; An Update

By Henk Wevers

Between the spring of 2002 and 2008 we observed ospreys settling our neighbourhood, on Colonel By Lake, north of Kingston Mills. This was reported in an article published in the June 2009 issue of The Blue Bill. Much has happened since that might be of interest.

From the time when the first pair of birds arrived in 2002 and successfully hatched their first offspring in 2004, they have brought up twenty-three young to date. Some of these have set up nests around the lake as shown on the map in Figure 1. This assumes, of course, that the first couple have now reached late adulthood and returned every spring, and that some of the young adults tend to nest in the area where they were brought up, after teaming up with mates from other families.

The first new pair to arrive in 2006 must have been two years old, which is the earliest couples form, and they built a nest on a large tree stump in the shallow waters at the east end of the lake. This nesting site was used until 2009 when the couple abandoned it. The pair produced one and then two young each year until they moved on. In 2010 we spotted a large nest on another tree stump in shallow water in the River Styx about one and a halve kilometre north-north east of the abandoned site; would this be the same “tree stump loving” pair? We can observe their activity only from a large distance, but the nest looks well built and we can spot the parents taking care of their brood in the years to date. Another keen observer, who operates from a kayak and can come closer to some locations, related to us that they have three chicks this season. 1

In 2007 another duo built a productive nest on the shore of Esther Bay, part of the watershed, between Colonel By Lake and the Aragon Road. It lasted until 2010 when a storm toppled the tree supporting the nest, with the loss of the brood. The next year, 2011, we assume with some confidence, this couple set up a household to the southeast, which is productive to date. See solid arrow.

Also in 2010 a nest was built in a large dead pine tree bordering Colonel By Lake on the western shore. It can be seen from Kingston Mills Road. From 2010 to date it has produced two offspring each year, we noticed again two chicks in early July.

A neighbour at the end of Aragon Road erected in 2009, on a large tract of land, two poles with a platform on each, offering more nesting sites. In 2011 one of these, nearest to the canal between Colonel By Lake and the river Styx, was occupied and it has been productive to date. We observed two young in early July.

There are now six occupied nests around Colonel By Lake and nearby River Styx. This might have been seven if one nest, on a high pole at the south side of the lake, was not taken away from an earlier osprey couple by two Canada geese! These geese arrive one or two weeks before the ospreys and start hatching their eggs in early March. Many more geese breed in the marshy areas of the lake and it is no wonder the geese population on our lake is increasing exponentially…

1 Mark Fleming, Aragon Road, Glenburnie, Ontario

1 In the meantime, the original pair of ospreys is now in their tenth year of breeding and we have a precise insight in their behaviour since we can observe their actions any time during the day from our deck, while we visit the other sites by boat, less frequently. It might therefore be worthwhile to report on the original couple in detail, as 2012 has been quite different from previous years.

The Original Couple…

On March 19th , earlier than in the past, we observe an osprey flying around the old nest site dating back to 2002. Three days later, while the weather is cold and rainy, one bird sits forlorn on the edge of the large nest, waiting… Just about a week later there are two ospreys and on April 3 we observe one of the parents, the female we assume, squatting deep in her nest. It is still cold, but we hope that this practiced adult will be able to hatch another batch. We have to wait and find out what the number of young birds will be this time…

Almost six-seven weeks later the parent is still sitting in the nest, but on May 25, we see one parent perching on the edge while the other sails high up in the air to look for prey. A little head is barely perceptible above the edge of the large nest. After a few days we confirm that there is only one chick.

The next day one bird flies in with a large stick in its beak to make the nest a little larger and the edge sturdier, who knows what the bird’s engineering instinct tells it to do? Below the platform on which the large nest is built we see a houseguest: a small bird flies in and out to bring up its own brood. The ospreys above are oblivious to the small intruder below. We have observed the same at another osprey site; the little bird flies past our boat hunting for insects, a tree swallow? In any case since ospreys viciously attack any larger bird entering their air space, the little bird’s household should be among the most secure anywhere!

On June 9th we can clearly see the chick taking food from its parent. It looks about one third the size of the adult. A week later a wobbly fledgling stands on the edge of the nest; it is now about half the size of the adult.

On June 27th the fledgling, almost adult size, perches alone on the edge of the nest, both Pa and Ma are hunting for food. With only one chick to feed this might be a much-deserved break from the hectic schedule for providing three young in one season, which happened most years.

Why would this couple only have one offspring this time around? All other times they had three chicks, except for one year when they had two. Are the parents growing old? They are, after all, in their tenth year of breeding. They arrived in our neck of the woods as a couple in 2002; they had grown up as singles over a two or three years period before they met and attempted to breed. Their first successful attempt was in 2003 but this did not last. Then in 2004, and in the following eight years, they returned each spring and bred successfully. Therefore they are most likely about twelve to fourteen years of age and they are now senior birds since the average

2 lifespan of ospreys is 14-20 years? 2The very early arrival, this year, or their age may have been the reason they only had one chick.

On June 30th the lone fledgling is practicing flight on the edge of the nest. The next day it is airborne and makes a small hop from on side to the other. When we look through our telescope again on July 8, the nest is empty.

The following days we see the threesome, two parents and fledgling, in trees nearby or soaring in the air, it must be an exhilarating experience to suddenly be a master of flight. The birds clearly enjoy soaring on the updrafts over land. We would love to see the parents teach its young to catch fish, but that happens beyond our sight. We did see an osprey diving several times unsuccessfully to try catching a fish. On the other hand we also see them regularly flying towards their nest with a fish, torpedo like in their claws. And because this one young grew up quickly, two or more weeks before the chicks in the other nests have matured to fledglings, there must be enough food to be caught and with some practice the young bird will thrive. Soon they will explore Collins Bay Lake to the northwest and the Cataraqui River towards the southwest and beyond.

Will the birds come back in the evening to enjoy some rest and life as a family? They usually do until late August, early September, when they appear to migrate to warmer areas to the southeast.

Only fifty percent of the young will on average survive their first year, there will be more loss over the years, but Colonel By Lake and its surroundings, appears to be attractive territory for the many osprey couples and their young.

2 United States National Museum, Bulletin 167, pages 352-379

3 The map shows Kingston Mills at the left margin, Colonel By Lake, Esther Bay to the north, and the canal connecting the lake with the River Styx. The nest sites are drawn in with the size of each star indicating the length of time they have been used. In the text box are the years of active breeding. We very much enjoy the expansion of the one nest starting in 2002 to six nests in 2012. Map overlay by Henk Wevers.

Nest on an old tree stump located in shallow water at the east end of Colonel By Lake. Photo credit: Jeff de Ruiter

The nest at the west shore of Colonel By Lake, all in the family… Photo credit: Henk Wevers