Editing Forster's tern (section)

==Behavior==

Forster's tern is often found in marshes over shallow open water.<ref name="Sibley" /> It is a shallow [[Seabird|plunge-diver]] that often hovers before attacking. When hunting, its head is pointed downward whereas when travelling, it is pointed forward.<ref name="ARKive" /><ref name="Salt" >Salt GW and Willard DE. 1971. The hunting behavior and success of Forster's Tern. Ecology. 52(6): 989–998.</ref>

It is a colonial nesting species that builds a shallow nest using marsh vegetation and often competes with gulls for nesting sites.<ref name="McNicholl71" >McNicholl MK. 1971. The breeding biology and ecology of forster's tern (Sterna forsteri) at delta, Manitoba. Thesis. Department of Zoology. University of Manitoba.</ref><ref name="McNicholl82" >McNicholl MK. 1982. Factors affecting reproductive success of Forster's Terns at Delta Marsh, Manitoba. Colonial Waterbirds. 5(1): 32–38.</ref><ref name="Strong" >Strong CM, Spear LB, Ryan TP and Dakin RE. 2004. Forster's Tern, Caspian Tern, and California Gull colonies in San Francisco Bay: Habitat use, numbers and trends, 1982-2003. Waterbirds. 27(4): 411–423.</ref> A breeding colony may vary in numbers from a few couples to a thousand individuals.<ref name="McNicholl71" /> In many occasions, Forster's tern will share nesting sites with the [[yellow-headed blackbird]].<ref name="McNicholl82" />

Both parents are involved in brood care and Forster's tern does not exhibit sex-specific differences in space use.<ref>{{cite journal|last1=Bluso-Demers|first1=J.|last2=Colwell|first2=M.A.|last3=Takekawa|first3=J.Y.|last4=Ackerman|first4=J.T.|year=2008|title=Space use by Forster's Terns breeding in South San Francisco Bay|journal=Waterbirds|volume=31|issue=3|pages=357-364|jstor=25148344}}</ref> Males tend to guard the nest more often during the day while the female is more present at night.<ref name="Bluso10" >Bluso-Demers JD, Ackerman JT and Takekawa JY. 2010. Colony attendance patterns by mated Forster's Terns Sterna forsteri using an automated data-logging receiver system. Ardea. 98(1): 59–65.</ref> When disturbed, newborn chicks tend to crouch and remain silent.<ref name="Hall" >Hall JA. 1988. Early chick mobility and brood movements in the Forster's Tern (Sterna forsteri). Journal of Field Ornithology. 59(3): 247–251.</ref> Forster's tern is a single prey loader and provision chicks with prey correlated to their size.<ref name="Fraser" >{{cite journal|last=Fraser|first=G.|year=1997|title=Feeding Ecology of Forster's Terns on Lake Osakis, Minnesota|journal=Colonial Waterbirds|volume=20|issue=1|pages=87-94|doi=10.2307/1521767}}</ref>

Before breeding, males practice [[Nuptial gift|courtship feeding]].<ref name="Fraser" />

===Vocalization===

The common call of the Forster's tern is a descending kerr.<ref name="ARKive" /><ref name="Cornell" /><ref name="Sibley" /> The threat call used in defensive attack is a low harsh zaar.<ref name="ARKive" /><ref name="Cornell" /> A succession of kerrs is used by the female as a begging call during courtship.<ref name="ARKive" />

===Diet and feeding===

The major constituent of Forster's tern diet is fish. Carp, minnow, [[Centrarchidae|sunfish]], trout, perch, [[killifish]], [[stickleback]] and [[Shiner (fish)|shiner]] are common prey in freshwater,<ref name="Fraser" /><ref>{{cite journal|last1=Taylor|first1=R.A.|last2=Wurtsbaugh|first2=W.A.|year=1991|title=Predation risk and the importance of cover for juvenile rainbow trout in lentic systems|journal=Transactions of the American Fisheries Society|volume=120|issue=6|pages=728-738|doi=10.1577/1548-8659(1991)120<0728:PRATIO>2.3.CO;2}}</ref> whereas [[pompano]], [[herring]], [[menhaden]] and [[shiner perch]] are often consumed in brackish or marine habitats.<ref name="McNicholl71" /><ref name="Fraser" /> On the West Coast of the United States and Canada, Forster's tern is also known to prey on Pacific lamprey juveniles.<ref><Close DA, Fitzpatrick MS and Li HW. 2002. The ecological and cultural importance of a species at risk of extinction, pacific lamprey. Fisheries. 27(7): 19–25.</ref> Insects such as dragonflies, [[caddisflies]] and grasshoppers are often consumed, but aquatic insect larvae, crustaceans and amphibian can complement the diet.<ref name="ARKive" /><ref name="McNicholl71" />

The Forster's tern is a shallow plunge-diver, having its head pointing downward when hunting.<ref name="ARKive" /><ref name="Salt" /> The attack usually starts in a hovering position before initiating a headfirst dive with wings partially folded backward.<ref name="Salt" /> Insects may occasionally be caught by the wing and prey are swallowed in the air.<ref name="Salt" /><ref name="Fraser" /> Prey handling behavior may include dropping and re-catching fish before swallowing them.<ref name="Salt" /> In some areas, Forster's tern tends to prefer forage to [[turbid]] water. This may prevent detection but it may also be a sign of higher prey density and increased presence near the surface. Preferences for water clarity may depend on prey availability.<ref>Henkel LA. 2006. Effects of water clarity on the distribution of marine birds in nearshore waters of Monterey Bay, California. Journal of Field Ornithology. 77(2): 151–156</ref>

===Reproduction===

The breeding season for Forster's tern can start as early as April on the Gulf Coast of the United States and extend from May to mid-June depending on latitude.<ref name="ARKive" /> Forster's tern is a colonial nester with colony size ranging from one to a thousand nests.<ref name="McNicholl71" /> Adults establish a very small territory around the nest and nests are usually clumped together.<ref name="ARKive" /><ref name="McNicholl71" /><ref name="McNicholl82" /> Males will practice courtship feeding and females will beg for food using a kerr kerr kerr call.<ref name="ARKive" /><ref name="Fraser" />

A typical clutch of eggs ranges from two to four.<ref name="Dakin" >Dakin RE. 2000. Nest site selection by Forster's terns (Sterna forsteri). Master's Theses. San Jose State University.
http://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=2980&context=etd_theses/></ref> The incubation period may last 24 or 25 days after laying.<ref name="Dakin" /><ref name="McNicholl83" >McNicholl, MK. 1983. Hatching of Forster's Terns. The Condor. 85(1): 50–52.</ref> The young are [[precocial|semi-precocial]] with shell removal being done by the parents.<ref name="McNicholl71" /> The chicks have upper- and lower-mandible egg teeth, which they lose three to five days after hatching.<ref name="McNicholl83" /> The chicks usually leave the nest with the parents four days post hatching and move into areas of denser vegetation.<ref name="Hall" /><ref name="Dakin" /> Fledging occurs 28 days after hatching.<ref name="Dakin" /> After a few weeks of fledging, young terns leave the natal colony but join the group for roosting, while migrating towards the wintering ground.<ref name="ARKive" /><ref>Ackerman JT, Bluso-Demers JD and Takekawa JY. 2009. Postfledging Forster's tern movements, habitat selection, and colony attendance in San Francisco Bay. The Condor. 111(1): 100–110.</ref>

There is a similar involvement from both male and female in incubation and chick rearing. Males tend to incubate the eggs diurnally and females, mostly nocturnally.<ref name="Bluso10" /> Reproductive success varies from year to year and from colony to colony.<ref name="McNicholl82" />

===Mobbing===

Forster's tern exhibits very aggressive behavior when threatened by nest predators; if a nest is disturbed, the colony [[mobbing (animal behavior)|mobs]] the aggressor, diving towards it and issuing loud calls.<ref>Siglin RJ and Weller MW. 1963. Comparative nest defense behavior of four species of marsh birds. The Condor. 65(5): 432–437.</ref> Aggressiveness increases immediately prior to and during hatching of the chicks. Ducks and grebes nesting in the same area often benefit from the tern's aggressive behavior toward potential predators <ref name="McNicholl71" />

Yellow-headed blackbirds sharing nesting sites have been known to actively join tern mobs against predators.<ref name="McNicholl82" /> [[Western grebe]]s recognize the tern's alarm call; this can be interpreted as information [[parasitism]].<ref>{{cite journal|last1=Nuechterlein |first1=GL.|year= 1981|title='Information parasitism' in mixed colonies of western grebes and Forster's terns. |journal=Animal Behaviour|volume=29|issue=4|pages= 985–989|doi=10.1016/S0003-3472(81)80051-6 |s2cid=53152999 }}</ref>