Breeding

Pair Formation

Variable in Florida, but most pairs form late Nov to early Jun; breeding season is long (≥ 8 mo) under favorable water conditions with abundant food resources (Sykes 1987c, Beissinger 1988, Snyder et al. 1989a). No information on percentage of unmated individuals.

Nest-Building

Time to construct nests 4–18 d (mean =11.2, SE = 1.2, n = 13 nests; Sykes 1987b), typically 2 wk (Beissinger 1987a), but can be longer when construction is interrupted (Chandler and Anderson 1974, Beissinger 1987a, Sykes 1987b). Completion generally is 0–5 d prior to initiation of egg-laying, but additional material may be added through egg-laying and incubation. Males do most nest-building.

First/Only Brood Per Season

Figure 6 . Nesting activity in all months of year, but not necessarily in same year. Breeding season varies widely from year to year in relation to rainfall and water levels. Most nesting attempts initiated Dec through Jul (98%) and 89% of attempts Jan–Jun, 1967–1994 (Sykes 1987c, Beissinger 1988, Snyder et al. 1989a, JAR, REB). Peak egg-laying Feb through Apr (Sykes 1987c).

Second Brood Per Season

Multiple nestings, mate desertion re-pairings, and renesting attempts occur regularly (Beissinger 1988, Snyder et al. 1989a). See Demography and Populations: number of broods reared per season.

Selection Process

Male selects site (Beissinger 1987a, Sykes 1987b).

Site Characteristics

Nest is almost always built over water, which deters predators (Sykes 1987b). Snail Kite nests in wide range of habitats within inland flooded freshwater marshes and other freshwater wetlands. Typical nesting habitat has surrounding low physiographic landscape near foraging areas. Nests are open or hidden, but with aerial access from above. Species nests in loose colonies or solitarily. Colonies vary in size and density and may be used for several years. Colonial nesting is often in association with nesting Anhingas, herons, or ibis. Snail Kites tend to nest on the periphery of such mixed assemblages. Nesting substrates over water include small trees, generally < 10 m in height (e.g., coastal-plain willow, bald cypress, pond cypress, punk-tree, sweetbay [Magnolia virginiana], red bay [Persea borbonia], pond apple, dahoon holly), shrubs (e.g., wax myrtle, cocoplum, buttonbush, Sesbania, elderberry [Sambucus simpsonii], Brazilian pepper [Schinus terebinthifolius]), sawgrass, cattails, bulrush, and reed (Nicholson 1926, Howell 1932, Stieglitz and Thompson 1967, Sykes 1987b, c, Beissinger 1988, Bennetts et al. 1988). Nesting substrates are alive or dead, or a combination.

During periods of low water, frequently builds nest in weak nonwoody substrates (e.g., cattails, sawgrass, bulrush, or reed), resulting in high rate of failure, particularly at Lakes Kissimmee and Okeechobee (Chandler and Anderson 1974, Sykes and Chandler 1974, Sykes 1987b, Beissinger 1986, 1988, Snyder et al. 1989a). Nests in herbaceous substrates are subject to collapse from wind and settling from weight of nests and birds. To counter this problem, wire basket-like structures mounted on a pole were developed (see Conservation and Management: Management). Nests prone to collapse were placed in such structures, which were readily accepted by Snail Kites (Sykes and Chandler 1974). Basketed nests were highly successful during low-water years, whereas those not manipulated usually failed (Beissinger 1988, Snyder et al. 1989a).

Height of nest rim above ground surface 0.9–4.2 m (mean = 2.1, SE = 0.06, n = 99; Sykes 1987b) and 0.9–12.4 m (mean = 2.2, SE = 0.06, n = 144; Bennetts et al. 1988). Water depths beneath nests ranged from 12 to 115 cm (mean = 52, SE = 1.8, n = 139; Sykes 1987b) and at time first egg was laid from 20–80 cm (n = 281; Bennetts et al. 1988). During breeding season, considerable fluctuation in water depths may occur. Depths at nests are usually ≥ 10 cm shallower than surrounding foraging areas (Bennetts et al. 1988). Flooding tends to reduce predation at Snail Kite nests by restricting movements and numbers of terrestrial predators (Beissinger 1986, Sykes 1987b).

Construction Process

Most nest-building is by males, with females assisting in structural maintenance following completion of initial construction (Beissinger 1987a, Sykes 1987b). Materials are gathered using feet or bill and generally are carried in bill 1 piece at a time to nest. Construction may take place throughout day but is most intense during morning hours.

Structure And Composition Matter

Large, bulky, loosely woven structure of dry sticks and other dry plant materials, elongate to globose, relatively flat rimmed, and open at top (Sykes 1987b, Beissinger 1988). Thirty-two species of plants are known to be used in construction, most common being dead sticks of coastal-plain willow and wax myrtle (Sykes 1987b), but this depends on what is available at a given site (PWS, JAR, REB). Cup is lined with finer dry plant materials (e.g., vines, leaves, herbaceous plants), including some green pieces (e.g., willow leaves, green stems, vines, sawgrass blades, grass). Sticks used are 10–92 cm long, sawgrass 10–43 cm long; dry weights of whole nests 662–1,964 g (n = 3) and total pieces comprising structures 276–803 (Sykes 1987b).

Dimensions

Outside diameter of nests 25–58 cm (mean = 41.6, SE = 0.7, n = 94) and thickness (height) 8–44 cm (22.7, 0.7, n = 92). Diameter of nest cup 7–20 cm (15.7, 0.3, n = 84) and cup depth 2–11 cm (6.1, 0.2, n = 84) (Sykes 1987b).

Microclimate

Nest is always built over water (Howell 1932, Stieglitz and Thompson 1967, Sykes 1987b, Beissinger 1988). Structure is relatively porous. Green materials continue to be added to cup into nestling period. Greenery of cup may help regulate humidity, influence temperatures during incubation and brooding newly hatched chicks, or aid in controlling nest parasites (Sykes 1987b). Nest is exposed from above or is partly shaded by foliage.

Maintenance Or Reuse Of Nests, Alternate Nest

New structure is generally built with each nesting attempt, but may be located in vicinity of or in exact site of a previous nest (Sykes 1987b); birds occasionally use previous nests (JAR). With renesting, a new nest may be placed near an unsuccessful one (Chandler and Anderson 1974).

Nonbreeding Nests

On occasion, nests are started but not finished or are finished and then abandoned (Chandler and Anderson 1974, Beissinger 1984, Snyder et al. 1989a).

Shape

Oblong oval; some tend to be short subelliptical.

Size

Sample of 317 eggs (117 clutches) had lengths of 40.2–50.5 mm (mean = 44.6, SE = 0.087) and breadths of 33.0–38.7 mm (36.1, 0.060) (Sykes 1987c); corresponds closely with Bent (1937) with mean length 44.2 and breadth 36.2 (n = 65).

Mass

For fresh whole egg 26.8–35.6 g (31.7, 0.357, n = 23), near hatching 24.4–28.8 g (26.5, 0.443, n = 9); whole egg volume 29–36 cc (31.6, 0.522, n = 14) (Sykes 1987c). At laying, a fresh egg is about 7% of adult female body mass (REB, PWS). Mean loss of egg mass (primarily water loss) during incubation is 16.3% (Sykes 1987c). Energy content averages 29.0 kcal/egg (Beissinger 1987a, 1988).

Color

Ground color dull white with splotches, speckles, and scrawls of varying shades of brown pigments with intensity ranging from relatively few markings to obscuring ground color.

Surface Texture

Smooth (Bent 1937, Sykes 1987b, Beissinger 1988).

Eggshell Thickness And Mass

Pre-DDT (prior to 1945), eggshell thickness 0.210–0.360 mm (mean = 0.264, SE = 0.003, n = 151 eggs, 50 clutches); post-DDT 0.213–0.323 mm (0.276, 0.004, 42 eggs, 27 clutches); eggshell mass pre-DDT 1.9–3.0 g (2.3, 0.032, 61 eggs, 20 clutches) and post-DDT 1.9–2.5 g (2.3, 0.027, 23 eggs, 17 clutches) (Sykes 1987c). No significant difference in loss of eggshell mass between pre- and post-DDT periods (Sykes 1987c).

Clutch Size

Range 1–6 eggs, average 3 (Nicholson 1926, Howell 1932, Bent 1937, Sykes 1987c, Beissinger 1988, Snyder et al. 1989a). Large clutches (4–6 eggs), particularly those of 4 and 5 eggs, were significantly more common before 1940 (Beissinger 1986, Sykes 1987c). One-, 4- and 5-egg clutches are now rare (Chandler and Anderson 1974, Beissinger 1986, 1988, Sykes 1987c, Snyder et al. 1989a). Only 1 clutch of 6 eggs described (Howell 1932). Smaller clutch size at present may relate to decline or instability of habitats since mid-1940s in Florida (Parker et al. 1955, Tebeau 1971, Blake 1980, Sykes 1983a, b, 1987c, Beissinger 1986).

Egg-Laying

First egg is laid soon after completion of nest or is delayed ≥ 1 wk (PWS). Eggs are usually laid between dawn and 1000 h. Eighteen 3-egg clutches (Jan–Jun) had laying intervals of 2–3 d (mean = 2.2, SE = 0.08), interval being the same within a clutch (Sykes 1987c). Laying intervals of 1–4 d reported (Chandler and Anderson 1974, Beissinger 1987a). Laying interval of 2 d is probably the norm, with 6 d to complete a 3-egg clutch. Intraspecific egg dumping is not known; eggs are guarded continuously during incubation (Beissinger 1987a, 1988).

Onset Of Broodiness And Incubation In Relation To Laying

Incubation begins any time after first egg is laid, but generally after second egg is laid (Sykes 1987c).

Incubation Patch

Present at least on female (REB).

Incubation Period

In Florida, 24–30 d (mean = 27.4, SE = 0.1, n = 21 nests; Sykes 1987c).

Parental Behavior

Incubation is shared by both sexes but varies among nests (Beissinger 1987b). Changeover occurs on or near nest accompanied by a soft ku-wak given once or twice by 1 or both members of pair. Female may also give low, short series of kaa-kaa-kaas . Both sexes frequently bring dry sticks, green twigs with leaves, or other materials to nest and present them to mate or place directly on nest. Male may bring incubating female extracted snails. Presentation of gifts usually accompanies nest relief. Sometimes female nibbles base of male’s bill or his head or neck feathers (Sykes 1987c).

Females tend to incubate at night (n = 200+ observations), but a few males will also (n = 8 observations, 3 nests). First changeover takes place within 1 h after dawn. Diurnal incubation interval 3–299 min (mean = 58 min, n = 57); no significant difference between pair members (Sykes 1987c). Beissinger (1987b) had male diurnal incubation >59% (n = 7 nests), female > 59% (n = 4), and sexes equal (n = 7), eggs uncovered 0–6 min, and mean incubation time (includes mate-deserted and non-mate-deserted nests) by males 55 min and females 50 min. In course of diurnal incubation, attending bird will sleep, rearrange nesting materials, preen, call to mate, watch other birds near nest, turn eggs, or change position. Incubating postures include head erect, head lowered with tail higher than head, or head lowered with chin resting on rim of nest. On average, changes in incubation position occur every 11.5 min; bird faces any compass direction with orientation independent of wind direction. Females turn eggs more frequently than males (87.5%, n = 14 observations, 3 pairs; Sykes 1987c).

Hardiness Of Eggs Against Temperature Stress

Little information. Birds generally incubate and protect eggs almost continuously once incubation begins. Sometimes, in middle of clear warm days, belly feathers of arriving bird are wet, perhaps to cool eggs (PWS). Eggs left unattended for 1–2 h during cool weather have hatched successfully (S. Beissinger pers. comm.).

Preliminary Events And Vocalizations

Chick can be heard calling inside egg 24–48 h before hatching (Sykes 1987c).

Emergence

Hatch asynchronously, in order of laying, generally in morning (Sykes 1987c). Interval between hatching of successive eggs in a clutch ranges from < 1 d to 6 d; emergence 6–14 h after egg is first pipped (Sykes 1987c).

Disposal Of Eggshells

Adults generally remove eggshells from nest following hatching; do not remove unhatched eggs (REB, JAR, PWS).

Hatching Success

Variable from year to year and between areas throughout peninsular Florida. Average 2.3 chicks/nest at hatching in clutches where ≥1 eggs hatched. Where at least 1 egg hatched, 2% hatched 1 egg, 13% 2 eggs, and 85% 3 eggs; in the one 4-egg clutch observed, 3 eggs hatched. No significant difference in hatching success between 2- and 3-egg clutches. Largest number of successful hatches were Feb (19%), Mar (31%), and Apr (23%) (Sykes 1987c).

Condition At Hatching

Semialtricial and nidicolous, downy, eyes open slightly, egg tooth present, mouth open, unable to stand, and barely capable of sitting and holding head erect to beg for food (PWS, JAR, REB). Within 24 h of hatching: mass 28.2–30.7 g (mean = 29.3, SE = 0.6, n = 4 chicks, 3 nests), length of exposed culmen (including cere) 12.6–14.0 mm (13.2, 0.4, n = 3, 2 nests), cere 4.8–5.9 mm (5.3, 0.4, n = 3), wing chord (unflattened) 17.3–17.9 mm (17.7, 0.2, n = 3), tarsus 17.0–17.9 mm (17.4, 0.3, n = 3), middle toe with claw 13.0–13.5 mm (13.2, 0.2, n = 3), and middle claw 3.0–3.7 mm (3.4, 0.2, n = 3) (PWS).

First of 2 downy plumages: soft, short, and buffy with tawny to light brown or brownish olive patches on central crown, along dorsal and caudal tracts, and on upper wing surfaces, and with black mask around eyes. Soft parts: iris dark brown, bill black, egg tooth white, cere and fleshy rictus dull yellow to orange, throat and tongue orange to scarlet orange, tarsus and toes dull yellow, claws light gray. Egg tooth retention is variable, 5–13 d (mean = 8.5, SE = 1.1, n = 6; PWS). Call is a soft cheep . Also see Beissinger 1988 .

Growth And Development

Nestling period 23–34 d (mean = 28.7) and, in same brood, interval between fledging of first and last nestling up to 5 d (mean = 2.3) and longer in a few cases (Sykes 1987c). Fledglings are fed by 1 or 2 parents until 9–11 wk old (Beissinger 1987b, Beissinger and Snyder 1987).

Mass Increase. Slow first 2 d, but linear thereafter until 19–20 d. Asymptotic mass varied, 370–470 g around 20–25 d, and regression occurred 24–30 d or just before fledging (Beissinger 1984). During cool rainy weather, mass increase slowed or actually decreased (PWS).

Growth of Body Parts. Culmen increases linearly until about 20 d; asymptote around 18–19 mm. Wing growth is curvilinear and does not cease before fledging (Beissinger 1984). Two linear equations for different periods of wing growth allow for accurate aging of nestlings to within 1 d: (1) before emergence of feather shafts (≤ 7 d), age in days = 0.319 wing chord + 4.289 (r²= 0.902, P < 0.001) and (2) with feathers emerged (> 7 d), age = 0.097 wing chord + 4.069 (r²= 0.972, P < 0.001) (Beissinger 1984, Snyder et al. 1989a). Beissinger and Snyder (1987) show differences in growth rates by brood size or parental care patterns (male vs. female deserters, or deserted vs. nondeserted nests).

Molt into Juvenal Plumage. Protoptile down is replaced by mesoptile at 3–4 d of age (PWS). Juvenal plumage (teleoptile), entire feathering, is fully developed by 4 wk of age (Beissinger 1988, PWS).

Ages When Contour Feathers Appear. First contour feathers are primaries and secondaries at age 4–6 d. Tail feathers first appear at 8–9 d, scapulohumeral tract at 9–12 d, and dorsal tract at 16–18 d. Feathers first appear at ventral tract at 18–21 d and on capital tract at 21–23 d (PWS).

Control of Body Temperature. Brooded until about 2 wk old (Beissinger 1988). During hot weather, chicks will pant with mouths open to thermoregulate (PWS, JAR, REB).

Behavior. See Food Habits: drinking, pellet-casting, and defecation; Behavior: locomotion, and self-maintenance; and Condition at Hatching, above. When food is scarce in Florida, larger siblings may dominate food supply brought to nest (PWS). Experimentally enlarged Snail Kite broods in Venezuela suggest that brood-size reduction may be result of starvation (Beissinger 1990a). No siblicide or infanticide documented.

Locomotion. Little information. Nestlings frequently stand and stretch wings, and 8–10 d before first leaving nest, they often stand on rim and exercise wings. Capable of short flights when they first leave nest at age 4–5.5 wk, but rarely capable of sustained flight until age 6–7 wk (Beissinger 1984, 1988, PWS, JAR, REB).

Brooding

Females brood more frequently and longer than males do, but extent of female domination varies from nest to nest (Beissinger 1984, 1987b); brooding decreases between weeks 1 and 2 (Beissinger 1984, 1987b, PWS, JAR, REB). Change in brooding over time is quantified in Beissinger 1987b . Average brooding (includes mate-deserted and non-mate-deserted nests) by males 18.7 min and by females 30.1 min (Beissinger 1984, 1987b).

Feeding

Young are fed through nestling period and after fledging until 9–11 wk old (Beissinger and Snyder 1987, Beissinger 1988). Feeding roles of males and females vary within nests day to day and between nests throughout nesting cycle (Beissinger 1987b). Males tend to do majority of snail capturing in first week, but variable thereafter (Beissinger 1987b, Sykes 1987a). Roles vary depending on which sex deserts, if any. Mean ± SD snail delivery rates/hour in Florida by brood sizes before and after desertion (n = 13) and at nondeserted nests (n = 5): 1 chick 1.6 ± 0.5, 1.6 ± 0.5, and 0.8 ± 0.4; 2 chicks 3.2 ± 1.1, 3.5 ± 1.0, and 4.4 ± 1.0; and 3 chicks 4.7 ± 1.4, 4.3 ± 1.5, and 3.5 ± 1.0. Rates are greatly affected by snail abundance and availability (Beissinger and Snyder 1987). When mate desertion occurs at age 3–6 wk, remaining parent provides 100% of food, usually at rate similar to that of both parents, until young can care for themselves (Beissinger 1987b). Feeding intervals 0.5–124 min (mean = 22.3, n = 267 observations; Sykes 1987a). Apple snails are only food observed fed to young in Florida; they are brought to nest 1 at a time, generally extracted from shell with viscera removed when chicks are young, and fed bill to bill (Sykes 1987a). In Venezuela, crabs are also fed to young (Mader 1981, Beissinger 1990b). At nest, extracted snail is torn into small pieces before feeding to chicks. Some snails are extracted by adult at or near nest (Sykes 1987a, S. R. Beissinger pers. comm.). Adults then start leaving whole snails at nest, initially with operculum removed and columellar muscle cut; later leave completely intact snails (Beissinger 1988). Larger chicks attempt to extract snails and soon learn to tear soft tissues into small pieces to swallow (Sykes 1987a).

Adult flying to a nest with snail is greeted by young with food-begging behavior which intensifies on approach; chicks face parent and lean forward with necks outstretched and sometimes with wings partly extended. Food-begging calls, high pitched and rasping, accompany above behavior; given throughout nestling period and ≥ 30 d after fledging. Adults arriving at nest with food give a kak-kak-kak call 1–3 times after chicks are several weeks old. After fledging, young may continue to use the old nest as a feeding platform (Sykes 1987a, PWS, JAR, REB).

Nest Sanitation

Once chicks are strong enough (> 10 d), they defecate over rim of nest. Pellets are sometimes found on nest (Sykes 1987a, PWS). Toward latter stage of nestling period, empty snail shells and occasionally whole snails in shells may accumulate on nest. One such nest contained 66 empty shells, 4 opercula, and 4 whole unextracted snails (Snyder and Snyder 1969).

Unknown. On rare occasions, however, unpaired birds are tolerated at or near nests; may assist with nest defense, etc. (JAR).

None known in Florida, either inter- or intraspecific. Black-headed Duck (Heteronetta atricapilla) in Argentina reported to lay eggs in Snail Kite nests (Hohn 1975). Hohn found 2 of 5 Snail Kite nests parasitized, and another worker at same locality had 30 Snail Kite nests with Black-headed Duck eggs, but Weller (1967a, b), in extensive studies of these 2 species, found no Snail Kite nests parasitized.

Departure From The Nest

Young leave nest at 4–5.5 wks, but may continue to use nest for many additional weeks for resting, feeding, etc. (Beissinger 1984, Sykes 1987c). Interval between fledging of first and last nestling in same brood is usually up to 5 d (Sykes 1987c) and up to 7 d in a few cases (Beissinger and Snyder 1987). Interval between fledging of siblings appears independent of brood size (Sykes 1987c).

Young leave nest about 1 wk before capable of sustained flight (Beissinger 1984, 1988). At this time, they can fly short distances and usually make awkward landings; tail feathers are often not full length (PWS).

First departure can occur at any time of day. May be short glide or weak flapping flight from nest or branches near nest to nearby vegetation, the landing generally unsteady. Young may perch for a time before making next attempt. At the time, parent may be perched near nest or flying low over site (PWS, JAR, REB).

Growth

Little information. Upon fledging, young are fully feathered and close to size of adults, may be heavier (370–470 g) than most adults, and tails may appear short (Beissinger 1984, PWS).

Association With Parents Or Other Young

Upon termination of parental care, young must care for themselves and develop hunting and feeding skills. May join other newly fledged young, foraging and roosting together, with or without adults (Beissinger 1988).

Ability To Get Around, Feed, And Care For Self

Capable of sustained flight at 6–7 wk (Beissinger 1984, 1988). At independence, somewhat proficient at capturing snails but unskilled at extraction. Mortality is low during this period if water levels are high and food is abundant, but if water is low or snails scarce, losses occur (Sykes 1979, 1987c, Beissinger 1986). Newly fledged Snail Kites often get tail, wings, and feathers of underparts wet hunting, and plumage may appear in disarray, a condition that does not generally occur with older birds (Sykes 1979). Independent young continue to hone their hunting and snail-handling skills (Beissinger 1988).

Fed by parent(s) until 9–11 wk old (Beissinger and Snyder 1987). Much daily movement by immatures and nonbreeding adults (REB). See Fledgling Stage.