Abstract:
A nest exclusion device is releasably attachable to a tower such as a cell tower, such that when installed it deters Osprey and other raptors from nesting on the tower structure, but is easily disengaged to permit worker access to the tower antenna mount structure, and can be easily reassembled. The device includes a center pole that extends upwardly away from the tower. A cap is attached to a top of the center pole, and a plurality of brackets are spaced about a periphery of the antenna mount structure with a maximum spacing between adjacent brackets of 18 inches. A plurality of cable assemblies extend from the cap to the brackets to define a tapering structure, converting the snag-shaped tower to a more conical shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/430,490, filed Jan. 6, 2011, the disclosure of which is hereby expressly incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    With the invention and broad adoption of cellular telephone technology over the last two decades, thousands of artificial metal cellular transmission towers have been constructed and placed across the North American continent and indeed, throughout the world. These structures may be owned and operated by the major telephone carriers, tower companies and/or smaller private tower owners. A typical cell tower is designed to support multiple cellular antennas and transmission equipment in an elevated position above the surrounding terrain. A cell tower typically includes an upright support, for example a monopole, and a horizontal antenna mounting structure known in the industry as a “crow&#39;s nest.” This structure is located at or near the top of the upright support and typically provides a working platform for tower personnel. There is often a railing system placed around the crow&#39;s nest for both worker safety and for attaching additional equipment, such as additional antennas and the like. The crow&#39;s nest frequently includes a floor or platform portion to facilitate inspection, maintenance, and upgrade of the installed equipment. The platform portion may include a handrail assembly for worker safety. The height of cell towers varies greatly, but typically they extend well above the top of existing structures in a given area. 
         [0003]    Examples of cell tower and crow&#39;s nest structures can be found, for example, in U.S. Pat. No. 5,954,305, to Calabro, U.S. Pat. No. 5,649,402, to Moore, and U.S. Pat. No. 6,563,475. Each of these patents is hereby incorporated by reference in its entirety. 
         [0004]    The Osprey ( Pandion haliaetus ) is a majestic raptor and one of the most widely distributed birds in the world. It can be found in both temperate and tropical regions on all continents except Antarctica. In North America, the Osprey is a relatively common raptor species, breeding in at least 34 states of the USA and in most provinces in Canada. It is particularly abundant along the Pacific and Atlantic coastlines. 
         [0005]    Migrant Ospreys generally arrive in the north during spring. They will breed during the boreal summer months and then return south to Central and South America in the fall. They feed primarily on fish and are most often found nesting near large bodies of fresh or salt water. 
         [0006]    Ospreys select tall, isolated and broken-off tree snags, often selecting Douglas Fir, Spruce or Ponderosa Pine for nesting. They build large nests, typically composed of a heap of sticks. This material is selected and transported to the nest primarily by the adult male and then carefully situated atop the snag by the adult female. She will place a wide assortment of other materials (grasses, sea-weed, even twine) directly on the rough upper end of the snag. 
         [0007]    Among raptor biologists, this species is known to exhibit a very strong nest philopatry, i.e., having a tenacious attachment to the same nest tree, year after year. Once a breeding pair is established at a particular nesting location, they can be quite difficult to dissuade from nesting at the same location in the future. 
         [0008]    With the now vast profusion of manmade towers, and especially cell towers, built in North America over the last two decades, the telecommunication industry has inadvertently created a profusion of attractive nesting sites for Ospreys. For example, from the perspective of an Osprey, cell towers mimic large, isolated nesting snags. Such manmade towers therefore “encourage” Ospreys to extend their breeding range into new areas containing these towers. This includes geographic locations where they have not previously nested, including highly populated urban areas, often situated miles from water. Based on the present inventor&#39;s experience, Ospreys are rapidly adopting manmade towers as nesting sites in ever increasing numbers. As a result of the unprecedented range expansion, they are creating many new and unexpected difficulties for the cellular telephone industry. A particularly troubling aspect of this phenomenon is the probability that those young Ospreys hatched and raised on cell towers will automatically imprint on them and, upon reaching adulthood, adopt the same type of structures for raising their families. We can therefore expect more and more manmade towers to become occupied by a geometrically increasing Osprey population over time. 
         [0009]    Under various international, federal and/or local laws, tower operators may have very limited options for responding when a raptor nests on a tower. For example, under the Federal Migratory Bird Treaty Act (MBTA), it is typically unlawful to take or disturb an active nest of a listed species (including Osprey) during the breeding season. This law is enforced by both State and Federal Wildlife authorities. Violators of the MBTA may be fined or even imprisoned for deliberate infractions of this law. As a result of this legislation, tower maintenance crews are legally prohibited from disturbing an active Osprey nest during the entirety of its breeding season, a period which may extend from February through September, an interval of seven months. Tower workers can be legally prevented from maintaining, repairing, or otherwise resolving any operational problems that may occur during this extended time period. 
         [0010]    In addition, many raptors can cause both disruption and damage to operating towers. Ospreys are large birds weighing up to 4 pounds and having a wingspan of over 4 feet. During the breeding season, they carry literally hundreds of large sticks and other materials to the tops of towers. 
         [0011]    During the nest construction process, Ospreys often drop foreign objects from a tower nesting site. This material may potentially strike workers below, or damage sensitive equipment located on or around the tower (e.g., transformers). Damage may be caused by direct impact, or direct electrical shorting of lines and/or insulators, or the like. Equipment at the top of the tower may also be damaged from impact or electrical shorting. There are many records of fires being started at Ospreys nests on electrical transmission towers caused by such shorts. 
         [0012]    In terms of hygiene, Osprey nests are inherently “messy” places. Over the course of a normal breeding season, a family of Ospreys (two adults and up to four young) create hygiene problems and other hazards for tower workers. For example, an Osprey nest may typically include an extensive amount of bird feces on, in, around, and below the nest. There will be whole and partially eaten prey items, including dead fish, and other prey. We have also found many dangerously sharp objects littering active nests, including barbed wire, dried fish bones, and rusted nails. 
         [0013]    Additional hazards to workers include the restriction of free and open access to the worksite atop the tower. Working at height is considered dangerous enough, but when physical movements are also limited and impeded by the presence of a large, often unstable mass of precariously balanced sticks, there is increased danger to the tower workers, both on and below the nest. Since Ospreys are known to add sticks to the nest each year, this danger will increase each summer as the nest increases in size, often substantially. The larger the nest becomes, the greater amount of mass is applied to a structure that may not have been designed to accommodate the additional weight, and associated stresses. This becomes particularly relevant in areas of North America that experience hurricanes. 
         [0014]    In addition to their own equipment, cell tower owners often rent space on their structures to several different clients, generating income from their investment. Interruption of services caused by nesting Ospreys, particularly on an annual basis, may cause the tenant to move to a different, more reliable tower site, causing a significant loss of revenue to the tower owner. 
         [0015]    More recently, bird strikes have become a major issue in aviation safety. For example, a well-publicized bird strike incident on 15 Jan. 2009, involving US Airways flight 1549 forced Captain Sullenberger to ditch an Airbus A320 aircraft in the Hudson River with 155 crew and passengers on board. The Federal Aviation Administration (FAA Advisory Circular 150/33B) has determined that Ospreys are a species of major concern for bird strikes. As such, Ospreys breeding near major airports present an especially dangerous hazard to aviation safety. For example, in June 2010, at Seattle-Tacoma International Airport in Washington State, an adult Osprey was struck by a jet aircraft on the runway. That strike was the major impetus for the creation of the invention disclosed herein. 
         [0016]    As a career raptor biologist, the present inventor has worked with birds of prey since 1965 in a variety of capacities, including nest surveys, migration studies, wintering investigations, and raptor banding. From 2001 through 2012, he developed and coordinated the Raptor Strike Avoidance Program at Sea-Tac Airport, working in association with the Port of Seattle. During this period they have captured, tagged, and safely re-located nearly 400 birds of prey to locations away from the runway. 
         [0017]    In 2004, a pair of Ospreys first moved into the vicinity of the airport. They adopted an inactive cell tower located southeast of the main runways. This was the first known Osprey nesting attempt in the vicinity of the airport. Although the birds attempted to construct a nest, they were not successful. In 2005, the pair returned to the same tower, completed a nest, and raised two young. Since Osprey, particularly recently fledged young, are known to be a major threat to aviation safety, a plan was implemented to remove the young Osprey from this nest at three weeks of age and re-locate them to a more suitable active nest, 40 miles north in Snohomish County, Washington, and well away from any active airport. This technique is known as “fostering” and was successful, the young being raised by their “foster” parents. However, the following year, the same adult Ospreys returned to the nest and bred. In 2009, a second pair of Ospreys adopted a cell tower located near the airport and began constructing another nest, although they were not successful in producing young. This event raised safety concerns among our group. We began to realize that nesting Ospreys were going to be an increasing problem in our area and that cell towers were obviously going to be their “road of ingress.” More Ospreys equated to increased aviation hazards. In 2010, this second pair returned and started to build and repair their nest once again. However, in June an adult Osprey (presumed to be one of these new adults) was struck by an aircraft on a runway not far from the nest. The bird was found alive but had lost a wing as a result of the strike. 
         [0018]    This specific incident confirmed our fears and focused the present inventor&#39;s attention on the safety issues involving Ospreys nesting in the vicinity of major airports. The present inventor recognized that the solution to the problem would be to provide an effective deterrent to Ospreys nesting on local cell towers. If we could prevent them from nesting nearby, then there would be far lower risk of aircraft strikes. The challenge was to provide an effective deterrent to Osprey nesting on cell towers that would not significantly interfere with the normal maintenance and operation of the cell tower. It is essential for tower workers to have a relatively unimpeded work area in the potentially dangerous and hazardous situation like a cell tower platform high above the ground. 
         [0019]    Because of these important emerging issues, the need for deterring Ospreys from adopting a cell tower prior to nesting becomes readily apparent. There is a need for a practical working device that will deter Osprey from building nests on cellular and other manmade towers. 
       SUMMARY 
       [0020]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0021]    A raptor nest exclusion device for tower structures includes a center pole with a cable retention cap that is configured to be installed at the top of the tower. A plurality of brackets are installed about the perimeter of the existing horizontally disposed structure at the top of the tower. Cable assemblies extend from the cap to the brackets, to define a tapering configuration that is intended to generally correspond with a healthy, complete tree top. The brackets are preferably installed with a maximum spacing between adjacent brackets of not more than 18 inches. The cable assemblies include a cable portion, a spring member, and a quick release that is configured to engage the bracket, such that the cable assemblies are easily release to allow worker access to the tower, and are easily replaced by the workers upon completion of their tasks. Preferably, the tapering configuration defined by the cable assemblies when installed, define an included angle of not more than 90 degrees. 
         [0022]    In an embodiment, the cable assemblies include a length-adjusting device, for example, a turnbuckle. The spring members maintain the cable assemblies in tension when installed, which tension may be adjusted with the turnbuckle. 
         [0023]    In an embodiment, the towers are cell towers, and the nest exclusion device is directed to deterring Osprey from nesting on the cell tower antenna mount structure. 
         [0024]    In an embodiment, the cap slidably fits over the top of the center pole, and includes a plate portion with a plurality of angled apertures that are disposed to slidably receive the cable assemblies. In an embodiment, the cable assemblies include an oversized stop on the distal end that directly engages the cap. 
         [0025]    In an embodiment, the nest exclusion device transforms an upper end of the tower from a generally horizontal, snag-like structure, to a tapered, treetop-like structure. 
         [0026]    In an embodiment, one or more of the cable assemblies are Y-shaped such that one end engages the cap, and the other two ends engage different bracket assemblies. 
         [0027]    In an embodiment, the bracket assemblies comprise a C-clamp configured to be attached to a periphery of the antenna mount structure, and having an eyelet bolt extending therefrom. 
         [0028]    In an embodiment, the invention includes a method for deterring Osprey from constructing a nest on a cell tower having an antenna mount structure, and includes installing a center pole with a cap on the cell tower, installing brackets onto a periphery of the antenna mount structure, and installing a plurality of cable assemblies that extend from the cap to the brackets, wherein the cable assemblies include a cable portion, a spring, and a quick release mechanism for releasably engaging the brackets. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0029]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0030]      FIG. 1  illustrates a conventional cell tower with an Osprey nest on the antenna mount; 
           [0031]      FIG. 2  shows an upper portion of a cell tower with a nest exclusion device in accordance with the present invention removably installed on the crow&#39;s nest or antenna mount; 
           [0032]      FIG. 3  is a front view of the nest exclusion device shown in  FIG. 2  installed on an antenna mount; 
           [0033]      FIG. 4  illustrates an exemplary cable assembly for the nest exclusion device shown in  FIG. 2 ; 
           [0034]      FIG. 5  is a cross-section detail view showing the cable retention cap for the nest exclusion device shown in  FIG. 2 ; 
           [0035]      FIG. 6  is a detail view illustrating an exemplary eyelet bracket assembly for the nest exclusion device shown in  FIG. 2 ; and 
           [0036]      FIG. 7  is a front view of another embodiment of a nest exclusion device in accordance with the present invention removably installed on an antenna mount. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    The key objectives for a workable nest exclusion device for working towers, such as cell towers, are: (i) To dissuade Osprey pairs from building a nest on the antenna mount (crow&#39;s nest) of the tower; (ii) To provide a device that is removable both quickly and easily to allow access and limit interference to tower workers at the antenna mount; and (iii) To provide a device that is easily and quickly replaced upon the completion of maintenance or other tasks on the tower. 
         [0038]    Unlike many other raptor species, Ospreys typically select a high, open, broken-off tree-top (snag) for building a nest. Such sites allow adult birds free and open access to the nest from all directions, which allows the large raptors to take advantage of the prevailing wind direction when approaching the nest. This allows the Osprey to easily deliver sticks to the nest and food to the young in an unencumbered manner. 
         [0039]    The horizontal superstructure (i.e., antenna mount) of many cell towers mimic the natural conditions favored by Ospreys for nesting. An exclusion device should radically change or alter the configuration of the cell tower from a substantially horizontal platform (that Osprey may equate to a broken-off tree snag) to a tapered or generally conical top (that the Osprey may equate to an unbroken tree top) so that the Ospreys will find the tower less desirable for nesting, and breed elsewhere. 
         [0040]      FIG. 1  shows a conventional cell tower  90  with an Osprey nest  80  shown on the antenna mount  92 . The cell tower comprises a tall upright support  91  having a platform or antenna mount  92  installed at an upper end of the upright support  91 . The antenna mount  92  typically includes a plurality of elongate peripherally located antenna pipes or posts  94  oriented vertically, to which the cell tower antenna  96  are mounted. The specific shape and configuration of cell towers varies considerably, and may include railing, floor structure, and the like. Osprey may find the antenna mount  92  ideal for building a nest  80 . The Osprey nest  80  typically comprises a large heap of sticks, tree limbs, driftwood and/or seaweed. Stick lengths of 18 inches and longer are common in an Osprey nest. 
         [0041]    A nest exclusion device  100  in accordance with the present invention is shown in  FIG. 2  attached to a cell tower  90 .  FIG. 3  shows a front view of the exclusion device  100  schematically with the antenna  96  and rearward cables and related structure omitted, for clarity. 
         [0042]    A main center pole or mast  102 , which may be formed from metal, fiberglass, composite or other suitable pole material, is installed typically directly over the tower upright support  91 . The center pole  102  may be attached directly to the upright support  91 , or may be attached to other support structure over the upright support  91 . For example, in a current embodiment a socket plate  108  sized to receive the bottom end of the center pole  102  is fixed to a top end of the upright support  91 . Preferably, the center pole  102  is length-adjustable such that the center pole  102  can be shortened or extended to accommodate different tower designs and dimensions. In a current embodiment, the center pole  102  is a telescoping pole with multiple aligned holes in both parts that permit the user to adjust the length of the center pole  102  by aligning the desired holes and inserting a pin, bolt or the like to achieve the desired length. Alternatively, the center pole  102  may be selected with the desired length for a particular cell tower application. 
         [0043]    The desired length of the center pole  102  will vary depending on the design of the particular cell tower. For example, a typical center pole  102  length may range from 3 to 10 feet. It is believed to be beneficial to select a center pole  102  length such that the largest angle defined by any two cable assemblies  120  (angle “A” in  FIG. 3 , hereinafter referred to as the included angle) is not more than 90 degrees, and in some embodiments not less than 60 degrees. The nest exclusion device  100  therefore transforms the shape of the upper end of the cell tower  90  from a relatively flat shape similar to a snag to a more conical shape similar to an unbroken tree top. 
         [0044]    In this embodiment, a cable-retention cap  110  is attached to the top end of the center pole  102 . The cap  110  has a tubular lower portion  112  that is sized to slide over the top end of the center pole  102 , and an attachment plate portion  114  engages a plurality of cable assemblies  120 . 
         [0045]    The plurality of exclusion cable assemblies  120  in the current embodiment comprise stainless steel wire cable having a minimum diameter of 3/32-inch to ⅛-inch. The thickness of the exclusion cable  120  is selected to provide sufficient strength to withstand the weight of large raptorial birds landing on the device  100 . The cable assemblies  120  extend from one side of the antenna mount  92  to the cap  110 . The cable assemblies  120  may attach to the hand rail  8 , to a peripheral post  94 , or to the antenna mount  92  platform. For example, in the embodiment shown in  FIG. 3 , some or all of the peripheral posts  94  have an eyelet bracket assembly  130  attached to an upper end. Additionally, eyelet bracket assemblies  130  are attached to the hand rail  98  at intermediate locations. Preferably, the maximum spacing between any two neighboring eyelet bracket assemblies  130  is less than or equal to about 18 inches. 
         [0046]    The maximum 18-inch spacing is selected to discourage Osprey from attempting to carry the relatively large sticks that are used to build a nest onto the antenna mount  92 . Providing a greater number of cable assemblies  120  to provide a smaller maximum spacing between bracket assemblies  130  will provide greater deterrence with the tradeoff of increasing the time and effort required for workers to remove and replace the cable assemblies  120  during maintenance. 
         [0047]    In a preferred embodiment, the center pole  102  and exclusion cable assemblies  120  of the exclusion device  100  are configured to define a generally tapered or conical shape that mimics the top of a coniferous tree and defines an included angle, for example, in the range of 60 to 90 degrees. 
         [0048]    An exemplary cable assembly  120  is shown in  FIG. 4 . The cable assembly  120  includes a cable portion  122  with a distal end having a larger diameter stop  124  attached thereto. A proximal end of the cable portion  122  forms a loop  125 . A spring  126  engages the loop  125 , and terminates with a hook element, for example a stainless steel carabiner-type ring or snap link  127 . The engagement ring  126  attaches to the cable  120  through the spring  126  to provide a desired tension in the cable assembly  120  and facilitate installation and removal of the cable assemblies  120 . Although not illustrated, it is contemplated, and may be preferred in many applications that the cable assembly  120  include a length-adjustment member such as a turnbuckle or the like. For example, a turnbuckle may be inserted between the cable portion  122  and the spring  126 . A turnbuckle provides means to adjust the tension in the cable assembly  130  for attachment to the railing  96 . It also provides an easier method to install and adjust the correct length of the cable  130  while working on the high elevation superstructure of the tower  90 . 
         [0049]      FIG. 5  is a cross-sectional detail view of the top end of the exclusion device  100 , showing the cable-retention cap  110  disposed on the center pole  102  and engaging several cable assemblies  120 . The cap  110  includes a plurality of angled through holes  115  that are sized and positioned to receive the cable assemblies  120 , and to engage the cable assembly stops  124  to retain the cable assembly  120 . The stops may be attached to the corresponding cable portion  122  after the cable portion  122  is inserted through the hole  115 , or the hole  115  may be provided with an oversized portion (not shown) that allows the stop to be threaded through the cap  110 , and then shifted to engage the cap  112  as illustrated in  FIG. 5 . 
         [0050]    A detailed view of an exemplary eyelet bracket assembly  130  is shown in  FIG. 6  attached to the hand rail  96  and to the cable assembly  120 . In this embodiment, the eyelet bracket assembly includes a C-clamp  131  having a first threaded aperture  132  on one arm that threadably engages an attachment bolt  133 . An opposite arm of the C-clamp  131  may be provided with gripping elements such as teeth  134 . The C-clamp  131  may therefore be positioned over a flange on the hand rail  96  and fixed thereto by tightening the attachment bolt  133 . The C-clamp  131  has a second threaded aperture  135  at its base that is threadably engaged with a hook member  136 . A locking nut  137  is provided to further secure the hook member  136  to the C-clamp  131 . The hook member  136  is sized to engage the snap link  127  of a cable assembly  120 . 
         [0051]    Of course, if the cell tower does not include hand rails, the bracket assemblies  130  may be attached directly to the antenna mount structure  192 . If cable assemblies are to be attached also to one or more of the peripheral posts  94 , eyelet bracket assemblies  130  sized and/or modified to attach to the posts  94  may be attached thereto. 
         [0052]    Installation of the exclusion device  100  will now be described with reference to  FIGS. 3-6 . When the exclusion device is initially installed, the socket plate  108  is installed directly to, or over, the cell tower upright support  91 . The center pole  102  is then inserted into the socket plate  108 , and may optionally be secured therein, for example, with a locking bolt or the like (not shown). If the center pole  102  is length-adjustable, the desired height for the particular application is set. As discussed above, the center pole  102  length is preferably set such that the cable assemblies  120  are disposed within an included angle of between 60 and 90 degrees. The bracket assemblies  130  are then fixed to the hand rails  96 , peripheral posts  94 , and/or antenna mount  92  at the desired spacing. As discussed above, preferably, the bracket assemblies  130  have a maximum spacing of about 18 inches or less. 
         [0053]    If the cable assemblies  120  are not already threaded through the apertures in the cable-retention cap  110 , they may now be assembled. The cap  110  is positioned over the top of the center pole  102 , and if desired locked into position. It is now a very easy and quick process to attach each of the cable assemblies  120  to a corresponding one of the bracket assemblies  130  by pulling the proximal end of the cable assembly  120  against the tension force of the spring  126  and engaging the snap link  127  to the associated hook member  136 . 
         [0054]    The top of the cell tower  90  will then present a generally conical shape to Osprey, which will not be perceived as a suitable nesting site. Moreover, if the bracket assemblies  130  are spaced not more than 18 inches apart, the cable assemblies  120  will make it difficult for an Osprey to transport similar-length sticks onto the antenna mount  92 . 
         [0055]    It will also be appreciated that when workers require access to the antenna mount  92 , e.g., for maintenance or upgrade, they can quickly and easily disconnect the cable assemblies  120  from the bracket assemblies  130 . The cable assemblies  120  may be readily stowed near the center pole  102  while maintenance is performed, and then the cable assemblies  120  may be reattached to corresponding bracket assemblies  130 . 
         [0056]    A front view of another embodiment of a nest exclusion device  200  in accordance with the present invention is shown in  FIG. 7 . This embodiment is similar in many specifics to the exclusion device  100  described above, and common aspects of the device will not be repeated. In this embodiment, some or all of the cable assemblies  120  are generally Y-shaped, wherein a first portion of the cable assembly  220  extends from the cap  110  to a bracket assembly  130 . A second portion of the cable assembly  221  branches away from an intermediate location, to engage an adjacent bracket assembly  130 . The second portion  221  may be formed integrally with the first portion, or may be spliced onto the first cable portion. Both cable portions  220 ,  221  include the spring  126  and snap link  127  shown  FIG. 4 . It is contemplated that more than one branching cable portion may be provided. The branching cable assembly  220  reduces the total material required for the nest exclusion device  200 , while still retaining the desired maximum cable spacing throughout the device  200 . 
         [0057]    In other alternative embodiments, the cap  110  on top of the center pole  102  may comprise a simple hoop (as disclosed in the provisional patent application incorporated by reference above) and the cable assemblies  120  may slidably extend through the hoop to engage an opposite side of the antenna mount structure  92 . Of course, branching cable assemblies may also be used with the hoop-type cap. 
         [0058]    While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.