This Week's Crops & Clips: Bald Eagles renovating nest

This is the seventh breeding season during which we have monitored a Bald Eagle nest near our south Florida home, the first recorded active Bald Eagle nest in Broward County in more than fifty years since before the use of DDT was prohibited.  

Several  attempts to install a nest camera have been unsuccessful, so all our observations are from the ground. Local eagle-watchers report their findings and post photos to my Bald Eagles of Broward County FORUM. You are invited to subscribe if you wish receive copies of observations as they are posted or in digest form.

Located in an exotic Australian Pine, the nest is massive.  Each year the eagles return to  enlarge and renovate it.



The eagles have produced at least eleven chicks, ten of which successfully fledged. Last season they hatched out two eaglets, but one disappeared when only two weeks old, and the second may have fledged at 86 days of age, before it was prepared for free flight, and was lost.

If you visit the above link to the FORUM you may see the data we compiled about the life events in this pair, whose nest is clearly visible from a main thoroughfare in Pembroke Pines, a little more than a mile away from our home. The nest site is located on City land. The eagle-watchers rallied successfully in support of its official designation as a Bald Eagle Sanctuary. 

This season, the eagles were first seen at their nest site on September 18, which is about average, and they started rebuilding the nest on October 15. Over the years they have laid their first egg between November 24 and as late as December 11.

Yesterday morning (October 30) Mary Lou and I arrived at the nest site at 9:05 AM  and found the male on the nest.



He flew off almost immediately but both male and female returned at 9:13 AM. We think it was the the male who brought in a large stick. The female watched as the male worked with the nest material for a short time.



Then the female flew down and joined him at 9:15 AM.





While both sexes have similar plumage, the female is larger and can also be distinguished by the profile of her head and beak. She has a higher forehead as compared to the male, whose bill and forehead are almost in line. The female's bill is also deeper at the base. When roosting her lower belly appears proportionately wider than that of the male. When not seen side by side, these subtle differences may not be easy to detect. 

Here, the female supervises as the male moves the stick. Is that a look of disapproval?



The pair worked together on nest construction until the female flew off at about 9:18 AM.



The female returned with a stick at 9:32 AM and the pair touched bills and postured in a recognition ritual that lasted less than a minute (the female is on the right).







The female then rearranged some sticks that the male had already placed.



However, they did work cooperatively.



Then at 9:35 the male pulled at a string that looks like monofilament fishing line, which could pose a hazard. This is worrisome, as an adult or eaglet could become hopelessly entangled.

My FLICKR photo collection from the eagle nest site includes other wildlife seen while standing watch.

Earthworms versus Ovenbirds

The Ovenbird has an unusual enemy in the lowly earthworm. Ovenbird breeding populations have declined in the far northern areas of its range in the US, particularly in the Great Lakes states. They were quite common when I started birding in New Jersey, where I recorded my first Ovenbird,  #58 in my life list, on  May 5, 1949. Back then, their "Teacher-Teacher-Teacher" song filled the woods during spring migration. 

In south Florida they are fairly common during spring and fall migration, and some remain here all winter.



However, after moving into our part-time home in northeastern Illinois, in 2007, I was surprised that they did not breed there and their songs were absent. On April 30 of this year, I saw my first Illinois Ovenbird, at Nelson Lake/Dick Young Forest Preserve in Batavia. It was the fourth sighting of an Ovenbird ever reported on eBird from this birding hotspot in 10 years, and the very first seen there during spring migration.

The decline in Ovenbird numbers has been attributed to the fragmentation of deciduous woodlands by development. There is less food for them on the edges and they prefer larger tracts of forest. However, recent research may have uncovered another important reason for their scarcity in some areas. 

During the last Ice Age, native earthworms were killed out in areas covered by the glaciers, and over the 11,000 years since the ice retreated they have extended their range northward very slowly, only about 1/2 mile in the last 100 years. In fact, no native earthworms have yet been found in the Great Lakes area of the US. 

The northern hardwood forests evolved in the absence of earthworms. Leaf litter accumulated under the trees, holding the moisture and providing an ideal substrate for herbaceous plants and native tree seedlings, among which the Ovenbirds hid their oven-shaped nests and found abundant food. 

This American Robin has caught a juicy alien tidbit in a park near our Illinois home:



Native earthworms face competition from invasive European earthworms, introduced by early settlers and spread in mulch, root balls and by commercial trade in "nightcrawlers" and "angleworms," used in compost piles and released by anglers. They now occupy the northern hardwood forests and have had a devastating effect on the habitat. Ironically, this is due to the very property that makes earthworms so valuable to gardeners as they break down waste vegetation, aerate and fertilize the soil. 

The enriched soil of the forest floor invites invasion by exotic plants that do not provide suitable nesting or foraging sites for Ovenbirds.  

"Researchers at the University of Minnesota, and elsewhere, have documented dramatic changes in native hardwood forest ecosystems when exotic earthworms invade. These changes including losses of native understory plant species and tree seedlings, changes in soil structure and declines in nutrient availability. There is also fascinating evidence emerging that the changes caused by exotic earthworms may lead to a cascade of other changes in the forest that affect small mammal, bird and amphibian populations, increase the impacts of herbivores like white-tailed deer, and facilitate invasions of other exotic species such as European slugs and exotic plants like buckthorn and garlic mustard. These results suggest that exotic earthworms may pose a grave threaten [sic] the biodiversity and long term stability of hardwood forest ecosystems in the region. Much more research is needed."  Ref: Earthworms to blame for decline of Ovenbirds in northern Midwest forests, study reveals  

Although grouped as members of the New World wood-warbler family, Ovenbirds lack the flamboyant coloration of many of that tribe, and mostly walk on the ground to find their food rather rather than hop through tree branches. 



Their legs are pale pink, and the Ovenbird often cocks up its short tail.



With an olive brown back and white breast streaked and speckled with black, they somewhat resemble tiny thrushes, but they have distinctive eye rings and an orange crown bordered by dark lines.



Sometimes there is very little orange on the crown, but the black streaks are very evident.



This is not mentioned in any of my field guides, but I notice that Ovenbirds' wings are very noisy. I can often hear one flying before I find it.



This one high-stepped along a branch, as if walking a high wire in the circus.

This week's Crops & Clips: Tricolored Heron

Around sunrise, a Tricolored Heron flew in and settled on an abandoned dock in the mitigation wetlands preserve next to our South Florida subdivision. It was too dark for decent photos, but I shot a sequence as it landed. They came out soft and blurry (ISO 1600, 1/800 sec at f/5.6) , but because the bird appeared so graceful, I could not bring myself to discard them. After much post-processing I recovered these images.









The heron then started to preen its feathers.



Here is another photo that needed "doctoring." It is actually an overlay of two photos of the same bird:



They were called "Louisiana Herons" in my early field guides, but they are not restricted to that State and they do display three prominent colors: red, white and blue. This youngster has more extensive rufous color on its neck than an adult, but it posed beautifully for me, reminding me of a John James Audubon painting!



Here is one in nice morning light:



They are common visitors to the edge of the lake at our back lawn.



Only about 20 feet away from our patio, I often must back up to include the entire bird in the viewfinder, as I do not have a zooming lens.



Insects make up a large portion of its diet. This Tricolored is stalking a Halloween Pennant dragonfly (click on photo to see location of the insect):



The heron crept stealthily towards the dragonfly, but it escaped the bird's grasp.



Video:The Tricolored Heron's foraging habits are quite distinctive:

If you see a blank area below, try clicking  HERE 



This video compares foraging habits of Tricolored and Little Blue Herons, side by side. Click HERE here if it does not load. 

A blighted birding patch

As is evident to anyone who reads my posts, our recent birding has been carried out within fairly restricted boundaries. In Illinois, it was our now extinct and lamented "back yard" prairie (Remembering birds in a vacant lot). In Florida, a convenient wetlands preserve adjacent to our subdivision is a scarred but welcome haven for resident and migratory species.

Since moving to south Florida in 2004 I have recorded a respectable 126 bird species in this local tract. Most are documented among over 5,500 photos that may be viewed in this FLICKR set: West Miramar Water Conservation Area

As happened with my Illinois "back yard" patch, this area is slated for massive development in the near future. This time it will not succumb to residential subdivisions or shopping centers. The mile-long stretch of gravel road that now provides access (Miramar Parkway/SW 196th Avenue right of way) will be paved and become a four-lane high speed parkway, to connect two major highways, I-75 and US-27. 

Most of the wetlands will be surrounded by 13-15 foot levees and flooded to a depth of up to 4-5 feet to become a huge retention reservoir. We hope that some terrestrial habitat is included in the project, to mimic the hardwood hammocks of the original Everglades. The Harbour Lakes mitigation area with its two lakes will remain outside the new reservoir, but the roadway will run along its eastern and northern edges.

This photo, which I took at sunrise just this past week, is the gravel right-of-way which will become the planned parkway.



The very spot, where I stood to take this picture of an immature Great Blue Heron and Great Egret with an assemblage of Roseate Spoonbills and White Pelicans in the Harbour Lakes wetland, will be paved and busy with traffic. 




The high levee will run along this row of abandoned telephone poles, dashing hopes that they might serve as sites for Osprey nest platforms. The open wet prairie to the right of the photo is part of the Harbour Lakes mitigation area that will not be included in the impoundment and presumably will continue to be actively maintained as a preserve.



Part of the US Army Corps of Engineers plan to restore sheet flow to the historic Everglades, the reservoir will serve to prevent diversion and seepage of rain water, which now flows in canals directly out of the Everglades to the ocean. The retained water will recharge the aquifer and keep salt water from intruding into the water table that supplies the residents and industries of the entire populated southeastern Florida peninsula. A system of pumps and waterways will regulate water flow, and biologic action in the standing water will remove agricultural pollutants such as phosphorus and nitrogen.

As this map illustrates, the reservoir, outlined in red and designated by the US Army Corps of Engineers as "Impoundment C-9," will be 3.5 miles from north to south, and up to 1.2 miles wide. LINK: The Broward County Water Preserve Area (BCWPA) is part of the Comprehensive Everglades Restoration Plan (CERP). 

To get an idea of the size of this project, US Highway 27 (Okeechobee Road), to the left, is about 5 miles west of Interstate I-75. At the northern edge, the small rectangular woodland that contains the Bald Eagle nest which we succeeded in having declared a sanctuary, will be spared.



Much of the land to be inundated had been "permanently" set aside by developers to compensate for the damage done to the Everglades by construction of subdivisions. 

The dedicated preserve consists of agricultural fields that, in the early 1900s, were "reclaimed" from the Everglades by draining and filling. Under the mitigation plan, these lands were subsequently managed to become a water conservation area. Drainage ditches were blocked and low levees were constructed around its perimeter. Exotic vegetation was removed. Although isolated from the main Everglades preserve (which is west of US-27) it collected rain water during the summer and dried out in winter, loosely mimicking the ebb and flow of the historic wild lands.

When we first came to Florida, the land was returning to a more natural state of wet prairie where Sawgrass and Spikerush flourished. With announcement of the C-9 project, all maintenance ceased and now the area designated for the reservoir is rapidly returning to a woodland populated by Australian Pine, Melaleuca, Brazilian Pepper and other invasive shrubs, grasses and vines. 

This is an example of one area that was a wet prairie only about 7 years ago. Now it is choked with shrubs.



After it is flooded, upland species such as Bobcat, White-tailed Deer will be evicted. This Bobcat eyed our approach as it sat right in the middle of the gravel road...

...and an eight-point buck peered out from the edge of the road.

Other upland species will lose their habitat, such as Raccoons...

...and Florida Box Turtles, both also captured as they ventured out on the roadway.



Of course, when the project is completed, it should support a rich habitat for fish-eating species such as herons, Osprey and Bald Eagles.

Tricolored Heron:



Osprey:



Bald Eagle with fish stolen from Osprey, on the Harbour Lakes mitigation area:



In the meantime, recreational off-road vehicle drivers are having their way with the wetlands, as efforts to restore them have been abandoned. Supposedly, under state law, these lands held "in perpetuity"  under deed restrictions and conservation easements will be replaced by "similar" acreage somewhere else in the State of Florida.

Before, during wet season:



Same location after visited by the all-terrain vehicles:



Another example, on posted water conservation easement (note that the "No Trespassing" sign has been knocked over by the fun-seekers):