Still Soaring

A REVIEW OF THE NATURAL HISTORY OF A REESTABLISHED POPULATION OF BREEDING BALD EAGLES IN NEW YORK.

Between 1976-1988, 198 nestling bald eagles (Haliaeetus leucocephalus) were reared and released by hacking at four locations within New York State. At the start of this project only one, unproductive nesting pair of bald eagles remained in New York, and the goal was set of reestablishing a self-sustaining breeding population. By the summer of 1989, 10 territorial adult pairs of eagles were identified within New York, nine of which nested resulting in the successful fledging of 10 young. Minimum survival of hacked eagles to adulthood (5 years of age) through 1990 is 16 percent or approximately one of six birds hacked. Minimum known mortality of all released eagles is also 16 percent (32 of 198). Observed turnover rate of nesting adults over the 10-year period 1980-1989 is seven percent. Fidelity to the region of release appears quite high, with male eagles establishing nesting territories significantly closer to release sites than female eagles. No hacked eagle has been found to be nesting farther than 388 km. from its release site. In many cases, hacked bald eagles have often chosen historic New York eagle nesting territories for their own breeding activities, and generally appear to be behaving similarly to other wild nesting eagles. Recent egg dates have been as early as 8 March in New York while unfledged Juveniles have been documented as late as 31 August in contrast to dates previously reported in The Atlas of Breeding Birds in New York of 16 March and 30 June.

New York State Department of Environmental Conservation, Delmar NY 12054

Peter E. Nye

Efforts to bolster and restore dwindling or extirpated populations of breeding bald eagles in the northeast United State began in Maine in 1974 with the transplant of two eggs from wild nests in Minnesota in exchange for two eggs in nests in Maine. By this time it had become obvious that bald eagles throughout the continental United States, and particularly in the northeast. Were suffering a dramatic decline. Due initially to habitat loss and due to persistent chemicals more recently. With the national ban on DDT in 1972 and simultaneous increased attention to endangered species, thoughts began to emerge about attempting to restore raptorial species, including the bald eagle, to vacant but suitable habitats. Three restoration techniques have been employed in this effort including egg transplants, fostering and hacking. Bald eagle hacking pioneered. In New York State in 1976, has been the most widespread and successful technique. It has become a popular and relatively straightforward method of releasing nesting age bald eagles into a given environment in hopes of reestablishing nesting pairs in the area. Hacking techniques have been amply described elsewhere, and can now be considered a valid management toll. The purpose of this paper is to provide an overview of the results of 13 years of bald eagle hacking in New York and to describe the characteristics of the reestablished breeding population. Historically many parts of New York especially the Adirondacks and the Great Lakes shorelines, provided suitable bald eagle nesting habitat. Large wetlands, such as those surrounding Oneida Lake, were favored locations. At least 74 locations have been confirmed to have nesting bald eagles since 1800. The size of the New York breeding population at anyone time is unknown, although it would seem reasonable that at least 50 to 100 pairs occurred here during the most suitable times.

By about 1960, only a dozen pairs were estimated to still exist, and by 1974, only a single non-productive pair remained in the entire state, at a location in Livingston County in western New York. Although barren, this last pair proved to be suitable foster parents and successfully accepted and fledged eight foster eagles over a five-year period Due to the lack of sufficient nesting birds to act as foster parents, however, hacking, or the hand-rearing to independence of nestling eagles in the absence of parent birds, was the primary option available for the attempted reestablishment of the species in New York. Between 1976 and 1988. 198 nestling eagles were reared and released by hacking at four sites within New York. Release sites were chosen in an effort to distribute birds into vacant but suitable habitat throughout the state, and included the following additional criteria.

I)) A clean, abundant fish food supply; usually one very accessible to inexperienced eagles

2) An area of limited or no human use or disturbance)

3) An area with documented historic eagle use and

4) An area suitable for nesting should hacked eagles survives and decides to do so

The vast majority of these birds (88%) were collected from wild nests in Alaska where the species is extremely abundant. Each eagle was fitted with a radio transmitter and a colored wing tag prior to release, allowing for tracking of movements and longer-term survival.

Movements of young, hacked bald eagles were carefully monitored and recorded indicating no clear preference as to direction or distance. Similar to movements studied of fledglings from wild nests at several other locations, which can be generally characterized as random wandering for at least the first few years of their life.

Overall know mortality of New York hacked eagles is 16% (32 of 198 birds), undoubtedly a minimum. The majority of all known deaths (79%) occurred within three months of fledging, corresponding to the time of early independence when all young raptors are known to be most vulnerable

The primary cause of death of New York hacked eagles has been shooting, accounting for 50% of all mortalities

Emaciation/starvation/or young eagles simply not learning to make it on their own, was the next leading cause of death, but only accounting for 25% of the cases. This is not surprising, and indeed was expected, since fledgling bald eagles typically spend from 3-12 weeks within the nesting territory honing their flight and prey-capturing abilities while watching their parents.

Other causes of mortality in order of magnitude included disease, suffocation electrocution and vehicle collision. On the brighter side, survival at least appears to be equaling mortality.

Sexual maturity in bald eagles generally occurs at five years of age, although can occur at four years, particularly in unstressed E.g. uncrowned) conditions. Of 150 potentially sexually mature New York hacked eagles (5 years of age through 1990). 16% (24) are definitely known to have survived to adulthood. Again, this number must be considered a minimum, since there are undoubtedly birds we are not aware of or that may have lost their wing tags and, therefore, are not countable. This represents a minimum survival to sexual maturity for approximately one of every six hacked eagles such data is extremely useful to others interested in establishing nesting bald eagles by hacking, and in particular how many eagles may need to be released in any given location. Adult survival seems to be skewed slightly to females (13 females versus 8 males, 3 sex unknown), for unknown reasons. During the hacking process, male eaglets are typically the most annoyed and stressed. Males are also known to fledge sooner and leave the hack site earlier than do females, which may decrease their survival chances.

The first New York hacked eagles began breeding in 1980, at age four, 146 km (91 mi) from their release site.

By 1990, 13 breeding pairs of bald eagles were confirmed within New York, all a direct result of hacking projects. In addition New York hacked eagles are currently nesting in at least two other locations outside of the state, in Pennsylvania and in New Hampshire.

Nearly 90% of all nesting New York hacked birds made their first nesting attempt at either four or five years of age. Fifty percent of all first time breeding attempts were Successful. Of 55 total breeding attempts by New York hacked eagles, 65% have been successful resulting in the fledging of 5I young, or 0.93 young per nesting attempt. These figures are extremely comparable to other wild eagle populations under study. The national recovery goal for the bald eagle is 1.00 young per breeding attempt. As our New York nesting birds gain in breeding experience (and provided they receive sufficient protection from human disturbance) we fully expect to exceed; this level. For example, for the 1990 breeding year. 12 pairs of eagles produced 15 young for a value of 1.25 young per nesting attempt

Known turnover of our adult breeders currently stands at only 5% over 13 year period, much less than in other raptorial species such as peregrine falcons. Wing tags have allowed this close, long-term monitoring of our New York hacked eagles. They have also provided us with significant insight into initial nest territory establishment: - these hacked birds, Seventeen New York hacked eagles (12 f, 5 m) have been positively identified as to release origin and subsequent nesting site although no favored direction could be detected of nest sites from release sites a sexual bias based upon distance is clearly expressed. Males exhibited a definite tendency to establish nesting territories close= to their release site than did females. Males moved an average of only 58 km (36 mi. range 0-146 km, 0-91 mi) while females moved ~~ average nearly 3 times greater, of 161 km (100 mi, range 14-386 km. 9-240 mi). The important lesson here is, if you want nesting eagles close to your release site, favor males. No hacked eagle has been found to be nesting further than 386 km (240 mi) from it release site.

The breeding chronology of recently reestablished New York nesting eagles has been found to be within the date-range consistent with our region, as opposed to dates expected from the locale of origin of these birds. In other words, transplanted Alaskan eagles adopt to the breeding chronology of their "new' surroundings. Recent egg dates have ranged from 8 March to 23 April. John Bull in "Birds of New York: State, lists a late egg date fully three weeks later, 14 May. This would result in fledglings in late September, which seems quite late for our region. Hatchlings have been observed between 16 April and 30 May. Fledged young have been confirmed from 15 July to as late as 31 August.

Again, bull cites fledglings from 20 May. This seems almost inconceivable since egg lying would have to have occurred around 15 January. Current New York nesting eagles are showing a clear preference for dominant, live, white pine trees. Forty seven percent of all nest trees selected have been white pines (7 of 15 trees) while other tree species have been chosen on only single occasions. Other species used include red Oak, red maple, silver maple, red pine, hemlock, and an elm snag. Height to the nests have ranged from 7.6 m (25') to 33.5 m (110'), with an average height of 22.4 m (73’)

Two current New York nesting situations bear special mention, both involving three adults. At one location, in an apparent display of polygamy, one male has been taking care of two females at separate nests; spaced approximately .5 km (1/3 mile) from each other.

For two consecutive years, the male has shared incubation duties with both females at both nests, and provided food to young at both nests in 1989 when two young successfully fledged from each nest. One of these two nests has failed this year due to an apparent infertile egg. The other nest has hatched young.

The second situation involves polyandry at a single nest site. Here, two males and a single female (note the three white heads) have been nesting, apparently quite harmoniously for four consecutive years The trio have successfully fledged five young during this time and are still together. The reasons for these unusual behaviors are unknown although the lack of a sufficient reservoir of breeding adults yet in the overall population may be a plausible explanation.

Although production of young is important within the context of an expanding bald eagle population, it is actually the survival of young and adult birds that is the critical determinant in population direction

Using a stochastic model for population growth developed by Grier, population parameters for hacked bald eagles in the eastern United States were input and three random situations covering a 20-year period were run to determine the direction of this nascent population

Two primary sets of survival conditions were applied to determine their affect: on population growth. The first assumed a 60% first-year mortality and 15% per year thereafter. The second assumed a 50% first-year mortality and only 10% thereafter.

Under condition 1, higher mortality (blue lines), the population shows early growth while young eagles are still being hacked. But it: levels off and begins to actually decline following the cessation of releases Under condition 2 (white lines), with more favorable survival conditions, the overall population continues to grow even once hacking has ceased.

Survival data accumulated for New York eagles thus far indicates that we are squarely within the survival range depicted under the growth scenario of condition 2.The New York breeding bald eagle population is currently expanding at an annual rate of between 25-75% per year Should this rate of growth continue, we will easily reach and surpass our recovery goal of: 40 -50 nesting pair by the mid-1990's. AN EAGLE. MUST

Pete -. District #l Thank you.

Pete Nye, A man that has dedicated his life to restoring the bald eagle to New York State wrote of his work (above) many years ago. Today in November 2007 we now have a count of 134 nesting pairs of bald eagles here in New York. The chance that more exists is very promising.

More on Pete Nye on the Endangered Species Unit of New York State. Link on my home page.

Lou Buscher