Breeding

Pair Formation

Timing unknown but some pair formation begins or continues after arrival at breeding colony, mid-Apr to mid-May.

Nest-Building

No specific information on duration of nest-building, but nest construction begins in pair formation and courtship displays (see Behavior: sexual behavior, above).

First/Only Brood Per Season

Figure 3 . For coastal Texas, median initiation date of first attempts 13 Apr (range 5–21 Apr, n = 50); for replacement clutches, median date 22 May (range 9 May–3 Jun; n = 30; King et al. 1991). For Maryland, egg dates 7 May–28 Jul (n = 697; Brinker 1996); for Iowa, egg-laying early May–mid-Jun (Bergman et al. 1970); for Wisconsin, 28 May–20 Jul (Robbins 1991); for Minnesota, egg-laying starting 13 May with 90% of pairs incubating 4–14 Jun (Fraser 1994a, 1997); for Manitoba, 27 May–11 Jul (MKM); for Ontario, 19 May–6 Jul (n = 33; Peck and James 1994).

Second/Later Broods Per Season

In Maryland study, after losses to flood tides, 100% (of 46 nests) in one year and 77% (of 17 nests) in following year, re-laid within 10 d (Storey 1987).

Selection

No information.

Microhabitat

In freshwater marshes, usually within clumps of vegetation, often adjacent or close to open water; on marshy shores of lakes, heaps of washed-up dead vegetation. Along Gulf Coast, nests on islands and coastal marshlands.

Site Characteristics

Ground nester. In freshwater marshes, nest built on muskrat lodges or on mats of floating vegetation (comprised of various species including algae, cattails [Typha sp.], bur-reed [Sparganium sp.], arrowhead [Sagittaria sp.], bulrush [Scirpus sp.], reed-grass [Phragmites sp.], sedge [Carex sp.], water lilies [Nymphaea sp.; Nymphaeaceae], and bladderwort [Utricularia sp.]; Ray 1901, Zuvanich 1963, Sprunt and Chamberlain 1970, McNicholl 1971, Hatch 1972, Thompson 1978, Scharf and Shugart 1984). Colonies on cobblestone islands in Columbia River, WA, nested on ground in or near scattered vegetation that included northern wormwood (Artemesia campestris), northern buckwheat (Eriogonum compositum) and Columbia River grindelia (Grindelia columbiana), lupines (Lupinus sp.), and mulberry (Morus alba); 40 of 72 nests had only cobble as substrate, 4 nests had only buckwheat, other nest substrates consisted of mixtures of cobble, buckwheat, grindelia, wormwood, sand, and/or lupine (Hall 1985, 1989, 1998).

In salt marshes and estuarine islands, also on windrows of vegetation, including cord grass (Spartina alterniflora, S. patens), dry eelgrass (Zostera marina), and sea oxeye (Boccichia frutescens; Spendelow and Patton 1988).

In management situations, artificial nest platforms (floating wood platforms 60 × 64 cm) have been put out and used (see Techlow 1986, Mossman 1989).

Construction Process

Little information except for Incipient Nest-Building or Scraping Behavior performed as part of terrestrial courtship displays (see Behavior: sexual behavior, above).

Structure And Composition Matter

Nests vary from unlined or sparsely lined scrape in mud or sand to vegetation comprising floating raft or on top of muskrat lodge. Nest may be little more than cup with no clear rim to more elaborate structure, built of marsh plants of the area. All nests at Delta Marsh, Manitoba, built of bulrushes (McNicholl 1971). Other studies report use of grass, reed-grass, bulrush, cattail, seaweed, sedge, or of other plants.

May use old grebe nests as nesting substrate (Bent 1921, van Rossem 1933, Campbell et al. 1990); reported to have usurped nest and buried Western Grebe eggs (Dawson and Bowles 1909) and to have used abandoned Pied-billed Grebe (Podilymbus podiceps) nest (with 2 grebe eggs; Zuvanich 1963).

Dimensions

In Manitoba, for 38 nests on muskrat houses, outside diameter 18.4 cm ± 9.5 SD (range 7.6–49.5) × 21.8 cm ± 10.7 SD (range 8.3–49.5), inside diameter 13.4 cm ± 13.5 SD (range 7.6–49.8) × 15.0 cm ± 8.4 SD (range 8.3–50.8); for 58 floating nests, outside diameter 32.6 cm ± 23.6 SD (range 7.6–114.3) × 42.7 cm ± 35.0 SD (range 10.2–188.0), inside diameter 11.7 cm ± 6.6 SD (range 7.0–58.4) × 13.2 cm ± 6.9 SD (range 8.9–58.4); for these 96 nests, cup depth 3.0 cm (range 0.0–7.0; McNicholl 1971). In Washington, for 72 nests built on cobblestone islands in Columbia River, outside diameter mean 22.4 cm ± 4.6 SD (range 15–42), inside diameter 11.9 cm ± 1.1 SD (range 9–14), cup depth 2.4 cm ± 0.5 SD (range 1.0–3.5; Hall 1985).

Microclimate

Little information; nest material may be soggy and eggs directly touching water (Harris 1933, McNicholl 1971).

Maintenance Or Reuse Of Nests

Rebuilding of nests washed apart in freshwater marsh colony rare (McNicholl 1971). During 3 h observation at colony in tidal marsh in Virginia prior to high tide, nest-building bouts seen during nest-relief at 4 of 10 nests, rather than in response to water under the nest site (Storey 1987).

Nonbreeding Nests

None reported.

Shape

Oval, short-oval, long-oval (Harrison 1979). Elongation ratio (length:breadth) average 1.40 ± 0.068 SD (range 1.08–1.57, n = 158), variation with 3-egg clutches higher than in 2-egg clutches (McNicholl 1971).

Size

Mean size for 158 eggs from Manitoba: 42.9 mm ± 1.8 SD (range 33.5–47.0) × 30.9 mm ± 0.7 SD (range 29.0–32.5; McNicholl 1971); for 31 eggs from Kansas: 43.4 mm (range 40.6–46.5) × 30.8 mm (range 29.1–32.2; Zuvanich 1963).

Mass

Mean 21.3 g ± 1.5 SD (range 18.6–23.7, n = 11; McNicholl 1971). Total mass of clutch about 40% of female body mass.

Color

Background color usually olive to buff or pinkish buff, marked with numerous small spots, blotches, crooked lines of dark brown, umber, or chocolate that often wreath larger end (Bent 1921, McNicholl 1971).

Surface Texture

Smooth, not glossy (Harrison 1979).

Eggshell Thickness

No published values. Although no measurements given, no statistical difference in eggshell thickness reported for samples from 1984, 1970, and pre-1943 (King et al. 1991).

Clutch Size

Usually 3, or 2, less frequently 1 or 4, rarely to 6; larger clutches (≥4) probably involve 2 females (Bent 1921, McNicholl 1971; see also Rockwell 1911). Mean clutch size: in Washington, 2.9 ± 0.39 SD (range 2–4 [single nest with 4 eggs had 5-d interval between first 2 and last 2 eggs]; n = 74; Hall 1985, 1989); in Manitoba, 2.7 eggs ± 0.47 SD (range 2–4, n = 77; McNicholl 1971); in Wisconsin, 2.54 eggs (n = 302 natural nets sites) and 2.99 eggs (n = 1,426 artificial nest platforms; Mossman 1989); in Iowa, 2.5 eggs ± 0.67 SD (n = 92; Bergman et al. 1970); in Maryland, clutch mean 2.6 eggs (range 2–4, n = 697; Brinker 1996); in Texas, 3.0 eggs (n = 127; King et al. 1991).

Egg-Laying

No precise data. Interval between eggs 1–2 d (MKM).

Onset Of Broodiness And Incubation

Begins day after first egg laid (MKM).

Incubation Patch

No information, presumably present in both sexes as is true for other tern species.

Incubation Period

In Iowa, average incubation period 24.2 d (n = 11; Bergman et al. 1970); in Manitoba, mean 25.3 d ± 2.02 SD (range 23–28, n = 13 clutches, measured as interval between laying and hatching of last laid egg; McNicholl 1983). In Wisconsin, ‘minimum incubation period’ (interval between laying of last egg and hatching of first egg), 20.83 d ± 1.75 SD (n = 23); for eggs artificially incubated, 37.7°C and 70% relative humidity, 20.13 d ± 2.85 SD (n = 15; Kubiak et al. 1989). In Cali-fornia, mean interval between hatching of first and second eggs, 1.8 d (n = 11); interval between first and third eggs, 2.0 d (n = 7; M. C. Coulter in McNicholl 1983).

Parental Behavior

Incubation by both sexes (MKM). Eggs covered >97% of time (Hall and Miller 1991); incubation duration average 69 min before adults change (n = 428; Fraser 1994a, 1997).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

No specific information. Incubating terns observed to wet feathers and return to nest (MKM).

Preliminary Events And Vocalizations

No information on embryonic development. Chicks begin to call (“Peep”; Discomfort vocalization, see Sounds: vocalizations, above) at or before Early Pip stage (see below) of hatching (McNicholl 1971, 1983).

Shell-Breaking And Emergence

Hatching process, from Early Pip (see below) to emergence, may extend over 1–5 d (mean 2.82 d ± 1.3 SD, n = 33); process begins when shell becomes slightly cracked (Early Pip; also called starring or cracking), continues until hole is present through which tip of bill can be seen (Pip stage); hole is enlarged in both directions from pip hole until opening encircles most of egg and cap can be pushed up (Ring stage) and chick emerges (McNicholl 1983).

Parental Assistance And Disposal Of Eggshells

No evidence of assistance; eggshells probably carried away (McNicholl 1971).

Condition At Hatching

Semi-precocial (eyes open at hatching, down covered, able to walk but stays in nest, fed by parents; Nice 1962) and nidicolous (stays in nest). Mean mass at hatching, for 15 eggs artificially incubated, 13.78 g ± 2.08 SD (Hoffman et al. 1987, Kubiak et al. 1989). Eyes open at hatching (MKM).

Growth And Development

Little information on growth of known-age young. Egg-teeth lost within 3–5 d of hatching (McNicholl 1983). On approach of observer (and presumably predator) to floating nests, chicks 1 and 2 d old crouch in nest, chicks 2 or 3 d old readily leave nest and hide in water; young from nests on muskrat lodges or platforms will hide on muskrat lodge or on platform (McNicholl 1971). In Oconto Co., WI, enclosures around 20 nests permitted measuring growth of young until when they could fly (at about 30 d posthatch): median mass and range for young age 5 d: 42 g (range 32–47); 10 d: 88 g (range 82–92); 15 d: 112 g (range 98–126); 20 d: 120 g (range 114–140); 25 d: 124 g (range 98–148; values estimated from Harris et al. 1993: Fig 2a).

Behavior

Little information. Hand-raised young yawned 5 min after hatching, made nibbling movement at 17 min; napped for most of its first 4 h; almost preened at 140 min and 180 min; on feet at 18 h (Nice 1962).

Brooding

Poorly documented; adults appear to brood young <3 d old and probably during stormy periods (McNicholl 1971). At Washington colonies, scans (normally 20 times/d between 07:00 and 14:30) of 15 nests with 1-d-old chicks indicate adults brooded 95% of time (n = 275 scans; Hall 1985).

Feeding

Both adults feed young. Size of fish correlated with age of young. In Minnesota, fish brought to 1-wk-old young averaged 3.3 cm; for older young, fish averaged 5.2 cm; young 1 or 2 wk old fed 2.3 fish/h, young 3 wk old fed 1.4 fish/h; most common prey yellow perch and shiners (Fraser 1997; see Food habits: diet, above).

Nest Sanitation

Feces not seen in nest nor were adults seen to remove any; bodies of all young dying in nest (excepting 1) remained in nest (McNicholl 1971).

Carrying Of Young

Not known to occur.

Not known to occur.

Eggs of Red-necked Grebe (Podiceps grisegena), Western Grebe, American Coot, and Caspian Tern in same nest with Forster’s Tern eggs likely represent nest takeovers by either species rather than actual brood parasitism by either participant (Finley 1917, van Rossem 1933, Semenchuk 1992).

Departure From Nest

In Washington colony on cobblestone island, chicks permanently left nest at age 4.1 d ± 1.4 SD (range 2–7; n = 33 chicks) when called by adults to another part of island; not capable of flight until 4–5 wk old (Hall 1988, 1989).

Growth

No information once young leave nest.

Association With Parents Or Other Young

Little information. Adults feeding flying young at Delta Marsh, Manitoba, always with 1–3 young (normal brood size), presumably their own but banding studies needed to confirm relationships (McNicholl 1971).

Ability To Get Around, Feed, And Care For Self

Little information. Fledged juveniles observed still begging for food in Florida after migration (Ogden 1969).

Little known of postfledging, prebreeding terns; lack of observations at northern breeding colonies (MKM) and sightings of 1 third-year (second summer) and several second-year (first summer) terns in Baja California, Mexico, in Jun (Howell and Webb 1995) suggest that immatures spend prebreeding summers at or near southern portions of species’ distribution.