Roseate spoonbill
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The colonially nesting Roseate Spoonbill (Platalea ajaja) is a medium-sized, pink-bodied, ibis-like bird with a flat spatula-shaped bill. These birds are found in the southeastern United States and West Indies through Mexico and Central America to South America, where they are distributed south to northern Argentina east of the Andes and in western Ecuador and northwestern Peru west of the Andes.
Throughout much of their range, the species is apparently declining as a result of habitat alteration, hunting, and pollution. In the United States, Roseate Spoonbills were common along the Gulf Coast in the early 19th Century, but were almost exterminated in the 1930s by intense persecution and destruction of wading bird colonies for the plume trade starting in the 1880s.
They were legally protected in the 1940s, after which populations recovered somewhat, but declines apparently followed later in the 20th century as a consequence of mosquito control programs and alteration of breeding and feeding habitats.
These highly gregarious waders feed by sweeping the bill side to side, often sifting through mud as they walk through shallow water. Their diet includes small fishes and aquatic invetebrates, as well as some plant material. They are found in coastal marshes, lagoons, mudflats, and mangrove keys, foraging in both salt and fresh water. Flocks typically include fewer than half a dozen individuals, but they are often associated with other wading birds as well.
In courtship, male and female spoonbills first interact aggressively, then perch close together, presenting sticks to each other and crossing and clasping bills. They typically nest in mangroves or other trees and shrubs 5 to 15 feet above ground or water, but sometimes nest on the ground. The nest, a bulky platform of sticks with a deep twig- and leaf-lined center, is built mainly by the female with material brought by the male,
Clutch size is 2 to 3 eggs, (range 1 to 5). The white eggs are spotted with brown. Eggs are incubated (by both sexes) for 22 to 24 days. Both parents feed the young. Young may leave the nest after 5 to 6 weeks and are capable of strong flight at around 7 to 8 weeks. .Roseate Spoonbils are mostly silent, but make a soft froglike croak when disturbed. (Matheu and del Hoyo 1992; Kaufman 1996; AOU 1998; Dunne 2006)
Behavior
The behavior of roseate spoonbills is not well documented. There is very little quantitative information and what is documented is not well understood.[1] Some breeding behaviors have appeared similar to that of other spoonbills, but further research into the behavior of roseate spoonbills and taxonomic relationships between spoonbills needs to be done.[1]
Roseate spoonbills forage using tacto-location to locate food while wading through shallow, muddy waters (National Audubon Society 2014).[1] In the early mornings and evenings, they slowly walk with their bill partially submerged, swinging it side to side, to sift out food from mud and water (Smithsonian n.d.; National Audubon Society 2014). The mandible contains nerve endings that snap the jaw shut as prey comes into contact with it (ARKive n.d.).
Catching prey by feeling, roseate spoonbills are able to forage without light, and thus their eye structure is not highly developed (Rojas et al. 1999). Roseate spoonbills eat smaller prey. This includes fish such as minnows and killifish; crustaceans such as shrimp, crayfish, and crabs; aquatic insects; mollusks; slugs; and plant material such as roots and stems (National Audubon Society 2014). If needed, roseate spoonbills may beat prey against a hard surface to aid in digestion (ARKive n.d.).
Roseate spoonbills preen using their bill to nibble and run down the length of each feather, starting with their lower neck and down to their breast and abdomen.[1] They clean their bill by dipping the tip in the water and then shaking their head to dry the bill.[1]
Sleeping occurs communally with the roseate spoonbills standing on one leg, with their head turned backward underneath feathers in their upper back.[1]
Members within a flock have been seen having a sham battle.[1] This interaction does not harm either fighter, and it is unknown why this behavior is done. In the sham battle, two birds fly at each other, and may rise about a meter off the ground as they beat their wings.[1]
When faced with a threat, roseate spoonbills alert conspecifics by standing tall with their neck outstretched and head held high.[1] An alarm call may come in addition with this stance to call further attention to the threat. When fighting a threat, they hold the axis of their body parallel to the ground with their head lowered, neck outstretched, and wings raised above their body.[1] Striking with their bill may result if the threat is intensified. One threat that causes this kind of behavior includes territorial defense against an encroaching member of an outside flock.[1]
Courtship for roseate spoonbills involves ritualized exchanges of nest material such as sticks and twigs from the male to the female to attract her and help her build a deeply cupped nest in vegetation above a water source (Smithsonian n.d.; TPWD n.d.). Males may head-bob and shake the stick as they deliver nesting materials to a female.[1] Females have been seen to beg for nesting materials with a bowing display.[1]
During courtship, the male and female first interact aggressively toward one another, but then proceed to perch close together with their bills crossed as the female begins to act submissively (National Audubon Society 2014).[1]
During the mating season, roseate spoonbills stay monogamous to their partner and both help to feed and take care of young (TPWD n.d.; National Audubon Society 2014). However, there is no evidence that mates stay together for multiple breeding seasons, suggesting that roseate spoonbills are seasonally monogamous (ARKive n.d.).
Only males have been seen to use defense mechanisms to defend a wide territory around his nesting site (ARKive n.d.; Prairie Research Institute n.d.). Defense mechanisms may include a threat posture and chasing other spoonbills.[1] Males will give up their territory rather than fight if threatened by other species.[1] Females will only defend the actual nest.[1]
In addition to mating displays, some displays are performed by the whole flock including up-flights and sky-gazing (Prairie Research Institute n.d.).[1] Up-flights occur after the flock performs an erect posture and then flies up and circles around their territory (National Audubon Society 2014). Sky-gazing occurs when another spoonbill is seen flying and individuals in the flock extend their neck and point their bill to the flying bird.[1] Neither of these group displays are well understood, but have been observed numerous times.
Distribution
The roseate spoonbill has an incredibly large distribution across the Americas, with its residential, or non-breeding, range spanning Argentina and Chile northward to the Texas Gulf Coast and Florida (Huey and Dronen, 1981; IUCN, 2001). There has never been a sighting outside of the Americas.[1] Many spoonbills are year-round residents of their respective areas, but some do tend to disperse before and after breeding season (IUCN, 2001).[1]
After breeding season, spoonbills in the U.S. disperse across Florida, Georgia, Louisiana, and Texas, making occasional stops in Alabama and Mississippi for the summer and fall.[1] Some spoonbills have even been reported as far north as Nebraska, Pennsylvania, Utah, Illinois, and Wisconsin (Allen, 1942; Lewis, 1983; FNAI, 2001). Although spoonbills are often residents in Florida, Texas, and Louisiana, there are fewer individuals present in the non-breeding season (Lewis, 1983).
In the winter, U.S. populations are restricted to the southernmost regions of the Gulf Coast, primarily in south Florida, southwest Louisiana, and coastal Texas.[1] Spoonbills are also relatively common in the islands of the Caribbean, except for the Lesser Antilles (FNAI, 2001).
There is little information on post-breeding dispersal outside of the U.S. and Central America, especially in South America.[1] Some think, however, that many roseate spoonbills migrate to Central and South America to avoid the cold climate (TPWD, n.d.; Howell and Webb, 1995).
Although their entire range is poorly documented in South America, spoonbills are known to inhabit some portion of each South American country at some time of year (IUCN, 2001).[1] Unlike the spoonbills of the U.S., the spoonbills in South America tend to prefer living and nesting inland around fresh water.[1]
Because little is known about the dispersal dynamics of different populations, some believe the South American populations are distinct from the resident populations in the USA and Central America.[1]
As for breeding range, in the U.S., the roseate spoonbill breeds along the coasts of Texas, Louisiana, and southern Florida. Outside of the U.S., spoonbills only seem to breed along the coasts of Mexico and Central American countries, although this is not well documented (Howell and Webb, 1995). Little information on breeding range is available in Central and South America.[1]
Habitat
Roseate spoonbills are aquatic wading birds with two distinct habitats: 1) feeding habitat, and 2) nesting and roosting habitat.
Their preferred feeding habitat is shallow water with a muddy substrate bottom (National Audubon Society, 2014). Since spoonbills use their elongate bill to sift through the mud for food and their ability to lean in is dictated by their height, the water must be shallow for them to successfully forage. The spoonbills’ tarsus, or lower leg, is typically 4.2 to 4.8 inches long, meaning that their preferred water depth is equal to or less than 4.7 inches, on average. When absolutely necessary, spoonbills will occasionally feed in deeper water, where their breast feathers and heads are fully immersed (Allen, 1942; Harrison, 1975; Lewis, 1983).
Spoonbills do not seem to be directly affected by salinity and will forage in a variety of hypersaline, marine, brackish, and freshwater habitats (Terres, 1980;FNAI, 2001).[1] Some specific locations include coastal bays, estuaries, lagoons, sea grass meadows, marsh, wet prairies, swamps, canals, tidal mudflats, tidal pools, sloughs, lakes, ponds, river drainages, mosquito control impoundments, catfish and crayfish ponds at farms, cattle ponds, and roadside ditches and puddles. (Allen, 1942; Terres, 1980; Britto and Bugoni, 2014; National Audubon Society, 2014).[1] One study in Florida found that spoonbills seem to prefer freshwater in some areas, which may be related to a limited ability to deal with hyperosmotic prey (Britto and Bugoni, 2014).
In attempt to stay far from potential disturbances and predators, spoonbills primarily nest and roost on islands, islets, or keys, in dense vegetation above ground or standing water (Lewis, 1983).[1] Although less preferable, spoonbills will also nest in shrub and forest wetlands on the mainland and occasionally in upland habitats farther inland (Lewis, 1983).[1] One study from Texas even noted spoonbills nesting directly on the ground (National Audubon Society, 2014).[1] Spoonbills do not require unique nesting habitat and are, in fact, known to nest in mixed-species colonies, so long as they are near suitable foraging habitat (FNAI. 2001; National Audubon Society, 2014).
No specific vegetation assemblage is essential, as spoonbills will construct their nests atop any low vegetation, trees, or shrubs with plant material that is abundant in the nesting location or nearby shoreline (White and Cromartie, 1982). Some studies have documented the different tree and shrub species spoonbills frequent for nesting, which include mangroves (Rhizophora spp. and Avicennia spp.), desert hackberry (Celtis pallida), marsh elder (Iva frutescens), bald cypress (Taxodium distichum), elderberry (Sambucus canadensis), sugar hackberry (Celtis laevigata), and willow oak (Quercus phellos) (Allen, 1942; White and Cromartie, 1982; Lewis, 1983).
As far as nest placement, spoonbills construct their nests on horizontal branches, five to fifteen feet above ground or water, on average (Allen, 1942; Lewis, 1983; National Audubon Society, 2014). The highest spoonbill nest recorded measured 98 feet above the ground (Lewis, 1983).
Although spoonbills require different habitat for feeding and nesting, there are no specific habitat requirements for mating. Spoonbills breed throughout their range in a variety of marine, brackish, and freshwater habitats. This includes habitats along the coast in bays/ estuaries, marshes, and beaches, as well as inland in forested swamps, rivers, lakes, and wet prairies (Terres, 1980).[1]
Some of the management practices necessary for maintaining preferable habitat for roseate spoonbills include—maintaining undisturbed/undeveloped areas, riparian habitat, and nature preserves; restricting human disturbance during migration,breeding, and nesting; controlling pollution in aquatic habitats; protecting existing wetlands and restoring degraded wetlands; prohibiting hunting; and providing protection from predators (Allen, 1942).
Management
According to the IUCN, the Roseate Spoonbill conservation status is currently of “least concern,” meaning that it is in no imminent danger of extinction (IUCN, 2001). However, the species should still be protected and subject to a strict management plan. Perhaps the most important conservation problem for this species is the degradation and destruction of coastal foraging and nesting habitat.[1]
In the late 1800s, hunting for the feather trade decimated the roseate spoonbill population. Although hunting is not currently an issue, hunting should continue to be prohibited (TPWD, n.d.).[1] One major step toward protecting roseate spoonbills was the US Migratory Bird Treaty Act of 1918, which now prohibits the taking of roseate spoonbills, their eggs, and their nests (FNAI, 2001).
Another major threat to roseate spoonbills is food availability, which is easily threatened by reduced fresh-water inflow and hypersalinity exceeding physiological tolerance of prey (White and Cromartie, 1982; Sundlof et al., 1994; Lorenz et al., 2009).[1] In addition to salinity issues, pesticides and other toxic contaminants such as organochlorides (DDT, DDD, dieldrin) and heavy metals (cadmium, lead), are harmful to both roseate spoonbills and their prey.[1] With proper coastal water management, however, these last two threats are manageable.
Overall, some of the management practices necessary for maintaining preferable habitat for roseate spoonbills include--maintaining undisturbed/undeveloped areas, riparian habitat, and nature preserves; restricting human disturbance during migration, breeding, and nesting by creating no-access buffer zones; controlling pollution in aquatic habitats; protecting existing wetlands and restoring degraded wetlands; prohibiting hunting; and providing protection from predators like feral dogs and raccoons (Allen, 1942; FNAI, 2001).
Some of the human activities that put the roseate spoonbill population at risk include--recreational development, channelization of streams, creation of locks and dams, dredging, increasing boat traffic, draining wetlands, applying pesticide on agricultural land, and deforestation (Allen, 1942).[1]
For now, the main goal should be the continual protection of the roseate spoonbill’s foraging and nesting habitat to ensure recruitment opportunities in the future (Allen, 1942).[1] In order to properly manage the roseate spoonbill population, a few aspects of their biology need to be thoroughly investigated. Some areas of future research should include nesting and breeding ecology, diet and foraging ecology, demographic parameters, population genetics, and behavioral repertoire.[1]
Threats
Currently, roseate spoonbills are under least concern on the IUCN Red list with a stable population (IUCN 2012). However, in the late 1800s, they were greatly threatened.
Between 1850 and 1890, roseate spoonbills saw their greatest population decrease. These wading birds were hunted for their feathers and meat (ARKive n.d.; Prairie Research Institute n.d.). Their feathers were used for fans and hats, and their meat provided food for fishermen and Indians.
Along with being hunted, their habitat was also destroyed by civilization and oil development (Prairie Research Institute n.d.). Sharing a habitat with hunted egrets was another cause for their population decrease because breeding colonies would be indirectly affected by hunters (ARKive n.d.).
Even though their population is currently stable, roseate spoonbills are suffering from habitat degradation and loss (Cornell Lab of Ornithology 2015; TPWD n.d.; Smithsonian n.d.).
Roseate spoonbills feed and nest in coastal marshes, lagoons, mudflats, and mangroves that are being highly altered from coastal development (Cornell Lab of Ornithology 2015; Smithsonian n.d.). Tourism in these newly developed areas further degrades the habitat of waterbird species. Roseate spoonbills have been observed to stay away from high traffic areas, which may affect their migration routes and breeding sites (Klein et al. 1995). Analyzing hydrological processes, nesting distribution, and reproductive success is important when conserving the habitat for the roseate spoonbill (Bjork and Powell 1994).
Along with habitat loss, parasitic helminths are also a cause for concern to roseate spoonbill populations. In Southern Florida, 89% of roseate spoonbills examined were found to be infected with parasitic helminths (Sepulveda et al. 1994). These parasites may come from the diet of roseate spoonbill populations and lead to pathogens for roseate spoonbills. Texas roseate spoonbills are not infected by similar helminth species as the Florida individuals. One cause for this may be a difference in diet, resulting in different parasites being present (Sepulveda et al. 1994). In Texas populations, nematode and cestode parasites have been found (Huey and Dronen 1981). Effects of these parasites is not well known but may lead to eggshell thinning, developmental issues, and increase in disease (Smithsonian n.d.).
As a result of polluted waters from increased development, the presence of mercury in roseate spoonbill livers has been observed (Sundlof et al. 1994). Increasingly polluted waters affect roseate spoonbills because it increases the concentration of contaminants such as mercury in fish species that constitute a large portion of their diet. Populations that eat larger fish accumulate a greater concentration of mercury in their systems due to biomagnification. Effects of mercury in wading birds include loss of motor skill, increase in diseases, decreased immune function, embryo mortality, and alterations in behavior (Audubon Society of the Everglades). Other toxins that may be of concern to the roseate spoonbill include cadmium, lead, and organochlorides.[1]
Predators can threaten the roseate spoonbill population if there is an increase in predator density. Common predators to roseate spoonbills include humans, raccoons, fish crows, great-tailed grackles, and the red imported fire ant (Solenopsis invicta) (Prairie Research Institute n.d.; Drees 1994). Many of these predators attack the eggs and nestlings of waterbirds. To decrease the effects of predators on prey populations, monitoring the interaction and population of each species is necessary. Some of these threats may worsen and lead to a susceptible roseate spoonbill population. In order to prevent this, systematic monitoring schemes, conservation sites, buffer zones, and water quality monitoring must continue (Florida Natural Areas Inventory 2001; IUCN 2012)
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References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 1.33 1.34 1.35 1.36 1.37 1.38 1.39 1.40 1.41 Dumas, J. V. 2000. Roseate spoonbill. The Birds of North America. Cornell Lab of Ornithology.
