Sunday, January 24, 2016

Saltie or freshie?

Black crowned night heron
Among the many important aspects of habitat selection that define the lives of water birds, salinity can be one of the most crucial.  Birds that exploit food resources in saline areas along the coast or in inland salt lakes require special physiological adaptations of the kidney, cloaca (end of the intestine where digestive materials and urine are mingled) and nasal salt glands.  
 


Clapper (rail)
We may recognize the ability of certain birds to tolerate high salinity habitats and use this as a means of predicting where they are found.   For example a large rail seen in salt water is likely a clapper, whereas in fresh water it would most probably be a king rail.
I
Adult male anhinga
saw an anhinga at our bayside dock recently and was surprised since this species is typically found in freshwater.  Of course Lemon Bay can be low in salinity after heavy rains, but in general it is near full strength sea water (32-35 ppt).  A relative of the anhinga, the double crested cormorant, on the other hand can live in both high salinity and low salinity environments.  Both feed on fish which are caught by swimming them down underwater. 

Red-breasted female merganser
Another type of fish eating diver is the merganser.  In SW FL we see wintering red breasted mergansers in salt water habitats and hooded mergansers in fresh water.  Yet red breasted mergansers migrate north to breed in Canada and Alaska in inland freshwater areas.  This type of switching in habitat salinity by season is also found in other species such as common loons which winter in salt water and breed in northern fresh water lakes. 
Yellow crowned night heron
Our two species of night herons also differ in their preference for saline versus fresh water habitats.  Along the SW FL coast, night herons found in salty habitats are generally yellow crowned night herons, which feed mostly on crabs.  In freshwater habitats black crowned night herons are predominant and feed on a wider variety of prey including frogs and reptiles.  But yellow crowns do occur in low salinity environments along the coast and inland in some localities where a freshwater crustacean, crayfish, may be eaten. 
Among the large terns there is a similar dichotomy in salinity preference/tolerance.  The royal tern can be seen at Englewood Beach and other coastal areas all year. 
 
Caspian, sandwich and royal terns
Whereas the slightly larger Caspian tern is usually found at fresh water areas such as the birding hot spots, Celery Fields or Myakka State Park.   But the Caspian can occasionally be found along the coast, especially during migration.  In my photo, comparing a single Caspian (with a more massive and redder bill) in the front foreground with a group of orange-billed royals, there is a single smaller sandwich tern (with light bill tip) which is a saltwater species all year.  
Cormorant on piling
The fact that birds can be separated into salt tolerant and intolerant species illustrates a common evolutionary theme, that physiological adaptations for coping with salt in the diet and drinking water are a major factor determining speciation.  This can be observed in the occurrence of closely related species, one of which is found in saline habitats and one in low salinity habitats.  If these were to interbreed, the genes coding for special adaptations for these dichotomous conditions would be muddled and the result would likely be a poorly adapted animal for either habitat. 
 
Common loon
So evolution tends to lead to separation into distinct species each tolerant of saline or freshwater environments and each living in those conditions for which it is best adapted. But the importance of long distance migration to these birds means that some species have adjusted to a switch in habitat salinity between northern latitude breeding and southern latitude non-breeding seasons. 
Bill Dunson
Englewood, FL and Galax, VA

Friday, January 22, 2016

Eight little cormorants sitting in a row‏




The pilings of the old bridge to Manasota Key, FL, now replaced by the Tom Adams bridge, are put to good use by double crested cormorants.  This row of seven pilings has eight cormorants sitting all in a row.   They catch their fish prey by out-swimming them underwater since birds have greater endurance than small fish.  Up close and personal, cormorants are attractive birds with huge feet (the better to swim with), and a stunning aquamarine-colored eye.

Bill Dunson

Great white heron catches a walking catfish




Most of the great blue herons that are so familiar to fishermen and beach goers are a dark morph, but rarely a white morph more typical of the FL Keys will show up.  One such great white heron has been hanging out at Myakka State Park.  I watched from the Myakka River bridge as this whitish beauty caught and carefully swallowed a spiny walking catfish, and seemed  to enjoy the treat with no apparent ill effects.   

Bill Dunson

Sunday, January 17, 2016

Wallking on water?‏




After a very stormy night as a cold front was passing through, there was a surprise along the shores of Lemon Bay, an extraordinarily high tide.  Most of those who have docks were to find at dawn that their docks were underwater.  Even finding the dock required "walking on water" with some care since older docks often float away during such events.  My neighbor's dock that was built to rise and fall with the tide was close to over-topping the poles built to hold it in place.

The cause of this unusually high tide does not appear to be primarily the lunar tides (high about 7:45 am was only around 0.7 feet, far below the maximum of 2.3 feet).  Instead strong winds changing from the west to northwest to north apparently both hold water in the bay at the inlets and tend to cause water to pile up at the south end of the bay. 

All in all a very exciting time for those who enjoy storms and unusual weather events.  This also could give us a preview of things to come as sea level rise is accelerated by global warming.

Bill Dunson

Osprey Murder Update‏

Female osprey returns after mate is killed.
After the discovery of the head of one of our beloved nesting ospreys on our front walk on Jan. 14, I surmised that a pair of great horned owls had killed it in the process of taking over the osprey nest.  This is an update to report on observations at the nest during the first day after this gruesome discovery.

Great horned owl eating male osprey
The surviving osprey is a female based on the dark markings on her breast, so the male must have been killed.  Although the killer(s) were assumed to be great horned owls, this became definitive when an owl flew to the nest site in the evening of Jan. 14 and began eating the body of the male osprey which was hanging in the Norfolk Island pine just below the nest.  My photo illustrates the face of the owl and the extended wing of the dead osprey below and to the right.  The female osprey flew close to the owl and repeatedly harassed it; the owl responded with bill snapping.

Female osprey returns to nest
The widowed female osprey returned to the nest site during the day of Jan. 15, but vocalized hardly at all, which is quite unusual.  In the late afternoon she perched on top of the pine and called, seemingly in defiance of the owls and the loss of her mate.  She flapped her wings and suddenly another osprey (sex unknown) flew by and she followed it.

The owls were calling that evening but have not yet taken residence in the nest.

Tune in for future updates to this fascinating story!

Bill Dunson
Englewood, FL

Friday, January 15, 2016

Shocking Avian Murder on Manasota Key

Osprey in Norfolk Island Pine nest
I was appalled by a gruesome discovery this morning just outside our front door.  The head of one of our magnificent ospreys had been severed and was lying on the ground.  A pair of ospreys has been nesting in a tall Norfolk Island pine directly over our house for the past 20 years.  I immediately suspected that the perpetrator was one of a pair of great horned owls that have been hooting from a stand of Australian pines next door.  

Osprey head killed by great horned owl
Great horns take over nests of other bird species and are well known to evict even large birds of prey such as ospreys and eagles.  We had heard a commotion in the early morning hours and thus surmise that one of the ospreys had been reluctant to abandon its cherished nest and was attacked and killed by the great horned owls.  These owls are huge and ferocious and completely dominating at night when they can see clearly while the daytime hunting ospreys cannot. 

Great horned owl
This is a painful lesson in the ways by which natural events sometimes unfold.  These can seem cruel, but conflicts over territory and breeding sites can be extremely fierce and terminal for the loser.  We are sad for our poor osprey but have been taught a lesson in nature's classroom.  

An interesting evolutionary question would be why great horned owls do not build their own nests as do most birds?  One answer would be that they thus save themselves some effort and can by their own might usurp the breeding territory of other birds.  There is of course no competition for food between ospreys (fish eaters) and great horned owls which feed on a wide variety of terrestrial vertebrate prey (birds, mammals, reptiles).  So the competition may be primarily for scarce nesting sites and/or perhaps even the nests themselves, which require considerable effort to construct.  

Water view of Norfolk Island Pine where osprey nest is located
There is also the fact that an owl nesting near an osprey or eagle would likely be subject to considerable harassment during daytime since the owls might prey on the osprey and eagle chicks.  So by removing the nesting osprey the owls eliminate a source of danger to themselves during daytime when they are most vulnerable.  

Bill Dunson

A visit to the yard of the "Butterfly Lady"‏

Mary Brown shows gulf frittilary caterpillars on passionvine
A group of local naturalists from the Peace River and Sarasota Butterfly Societies and some native plant enthusiasts were excited to visit the yard of Englewood, FL, resident Mary Brown who is famous for her skills in raising butterfly caterpillars, especially monarchs.  Mary cautioned us that her yard was small, but it was huge in terms of its bountiful caterpillars.  Indeed it is truly amazing what she has accomplished in a small space.  One advantage she has is that she is on the outer edge of a gated community which backs up against a large natural area currently being operated as a ranch.  Another is that she has a massive green thumb!  

Tiny gulf frittilary caterpillar and egg on passionvine
Her plants are luxurious, some of which are covered with small and large caterpillars.  Mary pointed out a beautiful passionvine which had many tiny just hatched caterpillars of Gulf fritillaries.  Species of passionflower are the only larval food for this and the zebra butterfly.  Monarchs on the other hand require milkweeds for caterpillar food.  Mary removes some caterpillars from her  outside plants (where they are subject to attacks from wasps, ants, spiders, birds and lizards) and brings them into a protected rearing cage where they feed on leaves from her yard.  She uses leaves of the giant exotic milkweed (Calotropis,http://lee.ifas.ufl.edu/Hort/GardenPubsAZ/Giant_Milkweed.pdf ) since they provide so much more food  than the native species or other exotics. After pupation the butterflies are released. 

Monarch caterpillar on giant milkweed
Even though it was morning of a cool day we saw an adult monarch flying by and a white peacock sunning itself to warm up.  Also a tropical skipper was seen sunning on the ground nearby.

Mary is to be commended for her exceptional gardening skills in raising butterflies and in providing a model for the rest of us to emulate.  Her latest project is planting of a large wildflower garden in a buffer area behind her house after the grass turf was removed.  This will be an intriguing experiment which we will follow with much interest.  It is an extension of her desire to conserve butterflies by providing nectar sources for the adults.

Small monarch caterpillar on tropical milkweed
Bill Dunson
Englewood, FL
Passionvine flower hosting gulf frittilary caterpillars

Rearing caterpillar cage at Mary Brown's

Tropical checkered skipper near Mary Brown's yard

White peacock caterpillar sunning in Mary Brown's yard

Saturday, January 9, 2016

St Joseph Snowy plover back at Stump Pass for second winter

I just today (1.9.16) found an old friend- a banded Snowy plover (Bands: left lower leg blue, right lower leg yellow/green, right upper leg metallic band).  It appears this is the same snowy seen by me previously at Stump Pass last year (2.22.15) and by Jeff Bouton (11.1.14) at Stump Pass State Park just across the inlet.
It is recorded as being banded as an adult male at St Joseph State Park in the FL panhandle 7.31.14 where it was likely breeding.  It was last seen there 9.17.14. 
It appears that this is the second winter that this snowy has been seen in the Stump Pass area (Charlotte County, FL).  A very nice demonstration of wintering site fidelity and for the suitability of northern Palm Island as wintering habitat!
This is an example of the type of shorebird that will potentially be affected by dredging and sand re-nourishment on Manasota, Palm and Don Pedro Islands. But these birds are highly adapted to the shifting sands of the beach and will move around in response to sand pumping activities.  It is even possible that they could benefit from food uncovered by sand dredging.  In any case if you observe this particular individual it can be identified by its distinctive and unique leg bands.  There is a second banded snowy plover in the same area with yellow/yellow on the left upper leg and orange/black on the right upper leg.  So keep an eye out for these and other banded shorebirds and report the sightings to bandedbirds.org 
If anyone else has records of this individual please let me know.
Cheers- Bill Dunson
Englewood, FL