Breeding

Phenology

Pair Formation

Varies geographically. In Puerto Rico, paired by Jan, when birds begin nesting (Lee 1989). Pairs observed in coastal Florida in Jan (Chase and Gore 1989). In coastal California, as early as mid-Feb; at Monterey Bay, CA, average pairing dates: 10 Mar for resident females (n= 6), 19 Mar for migrant females (n= 16), 6 Mar for resident males (n= 13), and 3 Apr for migrant males (n= 15) (JSW and JCW). Pairs observed scraping or scrapes found in coastal Orange and San Diego counties, CA as early as 20 Jan in 2008 (P. Knapp and E. Copper pers. comm.). In coastal Washington, pairs also reported by early Mar (Widrig 1980). Pairing is undoubtedly latest in northern Great Basin and Great Plains where spring arrival does not begin until late Mar or early Apr (Boyd 1972, Page et al. 1983, Hill 1985, Paton 1995).

Nest-Building

Since scraping is integral to courtship (see Behavior: sexual behavior) and nest construction (see Nest, below), timing of nest-building coincides with courtship.

First Brood Per Season

Figure 6. Nesting chronology varies geographically. Egg-laying begins in Jan in Puerto Rico (Lee 1989), about the second week of Mar in coastal Florida (Himes et al. 2006), by the last week of February in coastal Texas (Zdravkovic and Hecter 2004), and the first or second week of March on the U.S. Pacific coast. Unusually early nest initiation dates are 17 Feb 2002 in Florida (Himes et al. 2006), 23 Feb 2009 in coastal Orange Co., CA (P. Knapp pers. comm.), and 13 and 17 Feb 2008 in San Diego Co., CA (E. Copper pers. comm.); during a 5-yr study, the earliest nest in San Diego Co. was on 10 Mar and most nests were initiated from early Apr through mid Jun (Powell et al. 2002).

At Monterey Bay, CA, date of first egg in first clutches spanned a 24-day period from 5-28 Mar (median 15 Mar, n= 21 years) (LES). Egg laying also commences in Mar in coastal Humboldt Co., CA, where it occurs earlier on beaches than on river bars (Colwell et al. 2005), and as early as mid-Mar in coastal Oregon (Wilson-Jacobs and Meslow 1984). In deserts of s. California, clutches may be initiated by the first week of Mar (GWP), but in the Great Basin not until about third week of Apr at Mono Lake, CA (Page et al. 1983), or second week of Apr at Great Salt Lake, UT (Paton 1995). In the southern Great Basin, at Owens Lake, CA, nests are initiated as early as mid-March. After regions of the lake-bed were shallowly flooded for dust control, the onset of the nesting season did not change but the nesting season was extended with a higher proportion of nests initiated after the fourth week of May and in July (Ruhlen et al. 2006).

At Cheyenne Bottoms, KS, earliest egg on 22 Apr but most clutches not initiated until Jun (Boyd 1972), whereas commencement of laying at Great Salt Plains, OK, which is dependant on degree of habitat flooding, has varied annually from last week of Apr to mid-May (Hill 1985, pers. comm.). In the Playa Lakes Region of Texas clutches may be initiated as early as 7 April but most eggs are laid in May and June (Conway et al. 2005).

Second Brood Per Season

On the central California coast, where both sexes may double brood and females sometimes triple brood, females initiate second clutches as early as 26 Apr (median 18 May, n= 82) after successful hatch of first clutches, but not until 17 May (median 1 Jun, n= 33) if a replacement clutch was necessary for first brood of chicks. Corresponding dates for males were 15 May (median 6 Jun, n= 56) when first clutches hatched and 14 Jun (median 1 Jul, n= 13) when a replacement clutch was necessary (JSW and JCW).

Third Brood Per Season

On the central California coast, third broods of females initiated as early as 4 Jun (median 25 Jun, n= 19) after successful hatching of 2 previous clutches. After successfully hatching 2 clutches, no males initiated a third (JSW and JCW).

Over most of species’ range clutches are seldom initiated after mid-Jul (Boyd 1972, Page et al. 1983, Wilson-Jacobs and Meslow 1984, Hill 1985, Warriner et al. 1986, Lee 1989, Paton 1995), although in Florida egg-laying may extend up to the beginning of Sep in some years (Chase 1991). During 21 yr at Monterey Bay, CA, the last nest was initiated over the 12-day period from 10-21 July (median 15 July) (GWP). An unusually late initiation date for a nest was 24 Jul in San Diego County, CA (Powell 2001).

Nest Site

Selection Process

During courtship males usually make multiple scrapes, sometimes in widely separate territories; mean number per territory was 5.6 ±3.7 SD (range 1–15, n= 16) in coastal California (JSW and JCW). The scrape selected for most copulations, probably through female consent, typically becomes the nest site.

Microhabitat

See also Habitat. A ground-nesting species. Nests often located with respect to some conspicuous feature in fairly barren landscapes; e.g., near a piece of kelp, driftwood, clam shell, cow dropping, tumbleweed, or small growing plant (Boyd 1972, Purdue 1976a, Hill 1985, Page et al. 1985, Stern et al. 1990, Paton 1994a, J. Erbes in litt.); on small rises (Chase and Gore 1989, L. Hill pers. comm.), on small low dunes (J. Erbes in litt.); or in an area of peculiar substrate such as a patch of broken shell or glass (L. Hill pers. comm., GWP). Nests may be located under overhanging boards, branches, tufa, or live and dead plants, especially where there are high levels of avian clutch predation (Page et al. 1985, GWP).

In coastal Oregon, Snowy Plover nests were located in areas with significantly greater cover of driftwood and vegetation within 20 m of nests than at randomly selected beach sites (Wilson-Jacobs and Meslow 1984). Compared with random sites, Snowy Plovers in coastal San Diego Co. nested more by objects, in areas with more vegetation cover in beach and fill habitats, and in areas with more debris cover in beach and salt pan habitats (Powell 2001). In coastal Florida, 85 nests were all on beach slopes of less than 3° (J. Gore pers. comm.).

Site Characteristics

Snowy Plover nests on San Diego Co., CA, beaches were closer to water (53.5 m ± 2.4 SE) than those on fill (87.9 m ± 9.4 SE) (Powell 2001). In se. Colorado, nesting areas characterized by significantly lesser amounts of grass, litter and vegetation within 10 cm of the ground than Killdeer nests (Mabee and Estelle 2000). At the Salt Plains, OK, Snowy Plovers nest along seasonally ephemeral streams and are often found in lines of driftwood and other debris created by flooding of the creeks (Winton et al. 2000). At Owens Lake, CA nests were scattered on open dry alkaline flats but 105 of 164 were near distinctive features such as dry washes, sparse patches of salt grass, rocks, woody debris, unimproved roadways or vehicle tracks. Nests averaged 379 m ± 38 SE (n= 98) from water before areas of the lakebed were shallowly flooded to reduce dust emissions. Afterwards, many nests were located within the flooded areas and averaged only 8 m ± 1 SE (n= 89) from water; in areas of the lakebed that were not flooded nests averaged 425 m ± 72 SE (n= 28) from water (Ruhlen et al. 2006).

Nest

Construction Process

Male constructs nest depression in the ground by sitting and leaning forward on his breast and scratching with his feet while rotating his body. He can construct it in minutes. Nest lining is accumulated by males and females standing near scrape, picking up bits of debris in their bills, and tossing them backward over their shoulders or along side in one fluid motion toward scrape. While incubating, males and females pick up the debris in their bills and drop it in scrape. This activity commences prior to egg laying and continues through incubation period (Boyd 1972, JSW and JCW). In windy locations, scrapes frequently must be dug out again after being filled with blowing sand. On hard substrates birds rely on existing depressions (e.g., human or coyote footprints in dried mud) for their nest cups (L. Hill pers. comm., GWP).

Structure And Composition Matter

A natural or scraped depression on dry ground usually lined with 2- to 10-mm-long pebbles, shell fragments, fish bones, mud chips, vegetation fragments, or invertebrate skeletons. Linings are typically <10 mm thick, but JSW and JCW found 5 nests with a 20-mm-thick lining of Salicornia sp. elevating the eggs above wet mud in coastal salt ponds. Substrate on which nest are placed includes sandy beaches, cobble river bars, dried mud, crushed gravel road beds, shell mounds, and rarely, a depression in a log or on cracked asphalt on air fields (see Habitat for details).

Dimensions

At 174 Great Salt Lake, UT nests (PWCP), long diameter averaged 7.2 cm ± 1.5 SD (range 5.0–12.5), short diameter 6.8 cm ± 1.3 SD (range 4.5–12.0), and depth 1.4 cm ± 0.7.SD (range 0.5–3.0). Largest nests were found in old scrapes of larger shorebirds. Boyd (1972) reports 7–9 cm diameter and 1.0–2.5 cm depth for Kansas nests.

Microclimate

Although nests are often located near objects, these are usually too small to offer protection from weather (Purdue 1976b). Partial burial of eggs in nest lining in hot environments does not appear to have any thermoregulatory function for eggs (Grant 1982) but may help prevent them from blowing away in windy weather (R. Boyd pers. comm.).

Maintenance Or Reuse Of Nests, Alternate Nests

Snowy Plover nests are reused rarely and the wind typically destroys nest depressions on sandy beaches within days of hatching. Exact nest sites are sometimes used in consecutive years (PWCP, JSW and JCW). At a saline lake in Spain, Kentish Plovers occasionally deposited eggs in the scrapes of other females within 2 d after hatching or depredation of the original occupant’s eggs; 6% of 316 clutches involved utilization of existing nest scrapes (Fraga and Amat 1996).

Snowy Plovers continue to line their nests during incubation. When the lining was either experimentally increased or decreased, Kentish Plovers restored the original amount of material within 24 h at nests at Tuzla, Turkey. Neither incubation behavior nor internal egg temperature differed between experimental and control nests. It is speculated that the parents may balance the benefits of nest material for anti-predator and egg insulation functions against its potential for overheating eggs (Szentirmai and Székely 2002).

Nonbreeding Nests

Multiple scrapes are typically constructed for courtship before one is chosen for egg-laying.

Eggs

Shape

Oval to pyriform.

Size

For Snowy Plovers, based on 261 eggs from three-egg clutches of 87 females on the central California coast, mean length = 31.3 mm ± 1.0 SD (range 27.6–33.8) and width 22.7 mm ± 0.6 SD (range 21.0–24.2) (JSW and JCW). Roughly similar size in Kansas (Boyd 1972) and Oklahoma (Hill 1985).

For Kentish Plovers: on Hungarian grasslands, mean length = 32.0 mm ± 1.0 SD and width = 23.1 mm ± 0.4 SD (n= 64), and in Hungarian fish ponds mean length = 31.7 mm ± 1.3 SD (n= 31) and width = 23.1 mm ± 0.4 SD (Székely 1992); on Portuguese beaches mean length = 32.48 mm ± 1.19 SD, width = 23.27 ± 0.68 SD, and volume = 8.96 cm3 ± 0.64 SD, and on Portuguese salt flats, mean length = 32.47 mm ± 1.46 SD, width = 23.20 mm ± 0.56 SD, and volume = 8.91 cm3 ± 0.68 SD (Norte and Ramos 2004); and at a saline lake in Spain, mean length = 31.99 mm ± 0.11 SD (n= 751), width = 23.34 mm ± 0.06 SD, and volume = 8.96 cm3 ± 0.65 SD (Fraga and Amat 1996).

Egg size may vary seasonally. The average volume of Kentish Plover clutches increased with season at a saline lake in Spain (Fraga and Amat 1996) but there was no significant relationship between laying date and intra-clutch egg-size symmetry (Amat et al. 2001b). The length, width and volume of eggs in late clutches were smaller than earlier ones on a Portuguese beach (Norte and Ramos 2004). Within a Kentish Plover clutch, the second egg is reported to be typically larger than the other two in first clutches of the season (Amat et al. 2001b).

Egg size may vary with female size. The average clutch volume of Kentish Plovers increased with female size (based on culmen, tarsus, and wing length) at a saline lake in Spain (Amat et al. 2001a). Here, there was no difference in mean egg volume, or intra-clutch egg-size symmetry, between a female’s first and second clutches but there was a significant positive relationship between the mean egg volume of the second clutch and the interval between successive nests (Amat et al. 2001b); egg size was also positively related with female body condition, and was highly repeatable among clutches of females within and between years (Amat et al 2001a).

Mass

For Snowy Plovers, average fresh weight of 216 eggs from 72 females at Monterey Bay, CA was 8.5 g ± 0.5 SD (range 6.7–9.8); this was about 20% of weight of female, with 80.3% of variance attributable to interclutch and 19.7% to intraclutch variation (JSW and JCW). Egg mass for Kentish Plovers is reported as 8.9 g ± 0.5 SD (n= 28) at a saline grassland and 8.4 g ± 0.4 SD (n= 5) at fish ponds in Hungary (Székely 1992). Egg weight depends on stage of incubation; in Spain incubated eggs lost an average of 0.0474 g per day (Fraga and Amat 1996).

Color

Buffy to sandy background, lightly to moderately covered with small spots and scrawls, mostly dark brown to black, but also (in small proportion) gray. Spotting density increases toward larger end.

Surface Texture

Smooth and nonglossy.

Eggshell Thickness

Averaged 0.157 mm ± 0.008 SD (n= 6) in eggs from Salton Sea, CA in mid-1970s (Grant 1982). Morrison and Kiff (1979) found no evidence of eggshell thinning between pre- and post-DDT-period eggs from California.

Clutch Size

Usual clutch is 3 eggs (range 2–6) in Snowy and Kentish plovers. Unusually large clutches of 5-6 eggs may be the product of two females laying in the same scrape (Warriner et al. 1986, Fraga and Amat 1996). Single-egg clutches are almost always deserted (Warriner et al.1986, Fraga and Amat 1996). In Kentish Plover in Spain, mean clutch size, which was greater in first nests (2.9 ± 0.3 SD) than in replacement nests (2.8 ± 0.5 SD) (Amat et al. 1999b), generally declined over the breeding season (Fraga and Amat 1996). Kentish Plover clutches experimentally enlarged to 4 eggs took longer to incubate and showed lower rates of embryonic development than three-egg clutches (Székely et al. 1994). See also Demography And Populations: measures of breeding activity.

Egg-Laying

Snowy Plovers lay eggs during all hours of day and at night. In coastal California, the second egg of Snowy Plovers is more likely to be laid at night than first or third; intervals between eggs ranged from 46.5 to 118.0 h and averaged 61.6 h ± 11.9 SD (n= 8) between eggs 1 and 2 and 55.4 h ± 9.1 SD (n= 17) between eggs 2 and 3 (Warriner et al. 1986, JSW and JCW).

On California coast, Snowy Plover females spent 14–87 min (median 28 min, n= 32) sitting on the nest before laying an egg. Just before laying they often appeared restless and sometimes their wings quivered slightly 6–8 min before egg emerged. When some stood, contractions of lower abdomen could be seen while birds slowly raised and lowered their tails. If they were sitting on the nest, females depressed their tails on the edge of the nest as the egg emerged (JSW and JCW).

During egg-laying, adult Snowy Plovers may be absent from territories for more than a third of daylight hours (Warriner et al. 1986). Activities of adults in territory during egg-laying include sitting on partial clutches, territory and mate defense, feeding, preening, bathing, standing, sitting, and sleeping.

Interval between clutch loss and initiation of a replacement clutch by the same pair of Snowy Plovers averaged 7 d (range 6-8) in 12 of 13 instances from 1977-1982 at Monterey Bay, CA (Warriner et al. 1986). At the same location, from 1984-2001, the median and modal number of days until the first egg in the replacement clutch was 7 d (minimum 4 days) in 18 cases for which the exact date of clutch loss was known. Fourteen of the 18 nests were 8 or fewer days and the remainder were 22-44 d -- which could reflect missed clutches (LES). A new clutch may be initiated as few as 2–4 d after destruction of one that is incomplete (Warriner et al. 1986, M. Stern pers. comm.). For Kentish Plovers, 7-9 d elapse between the loss of a nest and the initiation of a new one (Székely and Lessells 1993, Amat et al. 1999b).

Intraspecific egg dumping is unusual in Snowy Plovers. Three clutches of 5–6 eggs reported from California coast probably represent cases of 2 females laying in the same scrape (Warriner et al. 1986). At Monterey Bay, CA, a pair of uniquely banded plovers had a nest with non-viable eggs that was incubated long past the projected hatch date. This same pair eventually initiated a new clutch of 2 eggs in the same nest, bringing the total to five eggs. The two eggs were clearly distinct from the first set of eggs which were “worn” and dirty in appearance (D. George in litt).

Instances of two females laying in the same scrape have also been reported for the Kentish Plover (Fraga and Amat 1996) and are indicated by DNA fingerprinting of eggs in Spain (Küpper et al. 2004). In s. Spain, 9 of 883 clutches contained eggs of more than one female: 3 six-egg nests, 1 five-egg nest, 3 four-egg nests, 1 three-egg nest, and 1 two-egg nest. In two of the six-egg nests, eggs of a second female were deposited after the three-egg nest of the original occupants had been deserted and both six-egg nests were eventually abandoned. In the other six-egg nest (which was eventually depredated), two females laid on alternate days. Two females laid eggs simultaneously in the five-egg nest which was deserted before incubation. All the remaining nests were incubated by one pair and 2 of the four-egg nests and the three-egg nest were successful (Amat 1998).

Mixed species clutches have has also been recorded in the Snowy Plover. Two Snowy Plover chicks and 1 Killdeer chick hatched from a three-egg clutch incubated by a Snowy Plover, but the fate of the chicks was undetermined (Agee 1997). At Oceano Dunes, San Luis Obispo Co., CA, in 2004, D. George (in litt.) observed a Least Tern incubating a 1-egg clutch. Subsequently, a pair of Snowy Plovers initiated a nest 18 inches from the tern nest and the plover sometimes left its nest to chase the Least Tern from its nest. The terns abandoned their nest and the plover(s) rolled the tern egg into their 3-egg nest and incubated all 4 eggs (eggs readily identifiable as 3 plover and 1 tern) for many days until all eggs were depredated by a coyote.

Incubation

Onset Of Broodiness And Incubation In Relation To Laying

Both sexes of the Snowy Plover intermittently sit on or stand over incomplete clutches; at 10 territories on central California coast, males averaged 16.6% ± 9.5 SD and females 10.3% ± 8.5 SD of daylight hours on incomplete clutches (Warriner et al. 1986). Sustained incubation typically begins when last egg is laid, although in rare instances up to 2 d elapse before it begins.

Incubation Patch

Both sexes have a single abdominal incubation patch.

Incubation Period

Varies with location and season. For Snowy Plovers on the California coast: mean = 27.4 d ± 1.5 SD, (range 26–32, n= 57) with average of 28.4 d compared to 26.9 d for early- versus late-season nests in the Monterey Bay area and up to 40 d when only one parent incubated (JCW, Warriner et al. 1986); an average of 28 d (range 26-33) and decreasing as the season progresses on the northern California coast where one nest incubated by a single parent took 38 d to hatch (Hoffmann 2005).

Great Basin, CA: mean = 26.9 d ± 2.5 SD, (range = 25–32, n= 9) with average of 28.8 d for 4 early-season nests and 25.4 d for 5 late-season nests (Page et al. 1979). Great Plains: in Kansas, mean = 25.5 d (range 24–26, n= 8; Boyd 1972); in Oklahoma, range 23–28 d (Hill 1985); and Florida: range 25–27 d (n= 30; Chase and Gore 1989). Two chicks hatched 49 d after incubation commenced at a s. California nest in 2003 (C. Sandoval in litt.).

For Kentish Plovers, the following incubation periods reported: mean = 27.2 (range 25-29, n= 6) in southern Spain (Fraga and Amat 1996); about 25 d at Tuzla, Turkey (Szentirmai et al. 2001).

Parental Behavior

In coastal California, the female Snowy Plover incubates during most of day and the male most of night (Warriner et al. 1986). In this cool climate, incubating adults sit on eggs, standing periodically to change position or rotate eggs. In hotter climates, birds frequently stand over eggs or sit on them after wetting their belly feathers in nearby water; both actions presumably prevent eggs from overheating (Boyd 1972, Purdue 1976a, Grant 1982). At Cheyenne Bottoms, KS, females incubate during most of day (Boyd 1972). At Great Salt Lake, UT, they tend to incubate in morning, whereas males often incubate in mid-afternoon and late evening; incubation bouts last 2-5 h during cool weather but as few as 10–15 min during hot weather (Paton 1995). At Great Salt Plains, parental shifts were in order of 8–16 h at temperatures <30°C compared to <1 h at temperatures ≥41°C (Purdue 1976b). Nest relief is often accompanied by debris tossing or head bowing by one or both adults (Boyd 1972, JSW and JCW).

At 8 territories on central California coast, Snowy Plover males averaged 9.5% ± 9.3 SD and females 79.7% ± 9.6 SD of daylight hours incubating completed clutches (Warriner et al. 1986). In coastal Humboldt Co., CA, daytime nest attentiveness for female Snowy Plovers averaged 91% ± 17 SD; females incubated 31-100% of the time and averaged 1.4 ± 1.4 SD recesses per hour; recess duration averaged 2.1 min ± 4.1 SD; of the recesses, 20% were unrelated to any apparent cause, 48% were caused by potential egg predators, 11% by humans, and 18% were considered caused by unknown disturbances (Hoffmann 2005).

Daytime incubation by females and nighttime incubation by males also characterizes the incubation pattern of the Kentish Plover (Fraga and Amat 1996, Szentirmai et al 2001, Kosztolányi and Székely 2002). Females relieve their incubating mate at dawn when the ambient temperature is low (Szentirmai et al 2001). In southern Spain, probability of diurnal incubation by the male increased with ambient temperature in exposed nests but not at shaded ones; thermoregulatory behavior used by birds incubating in the open to dissipate heat includes gaping, panting, standing, ptiloerection, wing dropping and belly soaking; birds incubating in shade did not exhibit any of these thermoregulatory behaviors (Amat and Masero 2004); male incubation time increased as the season progressed and became hotter (Fraga and Amat 1996). In Hungary, during daylight, both sexes combined spent 91.7% ± 2.1 SE in 1991 and 96.4% ± 1.6 SE in 1992 of the time incubating; female share was 73.0% ± 12.2 SE and 71.5 ± 12.9 SE, respectively (Székely et al. 1994a). At Tuzla Turkey, females spent 11.3 h per day incubating compared to 9.4 h by males; male incubation bouts averaged 50.2 min (range 29.1-188.7) and female’s 75.3 min (range 30.2-231.0) (Kosztolányi and Székely 2002). After experimental removal of one incubating parent from nests in Turkey, single-parent clutches were incubated less during daytime than control nests with two parents; after mate removal, males spent more time incubating and female incubation time did not change; although males spent more time incubating during daytime after mate removal, the increase was not sufficient to make up for the prior contribution of their mates (Kosztolányi et al. 2003).

Following the death or desertion of their mate, the remaining Snowy or Kentish plover parent usually deserts the clutch; however, some birds of both sexes incubate alone especially if they lose their mate late in the incubation period (Warriner et al. 1986). Unassisted male Kentish Plovers are reported to incubate alone up to 13 d and females up to 9 d (Kosztolányi et al. 2003).

Hypotheses for the diurnal pattern of incubation of Kentish and Snowy plovers include: the need for females to forage at night to recover an energy deficit from egg laying; the need for males to spend daylight hours defending nest territories from conspecifics; an advantage from the less brightly colored female being less visible to daytime predators; and, possibly, a greater ability of males to detect and distract nocturnal nest predators (Kostolányi and Székely 2002).

Hardiness Of Eggs

Temperature of attended Snowy Plover eggs fluctuates with ambient air temperature; eggs are probably less resistant to overheating than to cooling (Purdue 1976a, Grant 1982). In Kentish Plover the temperature of eggs is also strongly affected by ambient temperature; thus egg temperature differs between morning and afternoon (Szentirmai and Székely 2002).

Hatching

Preliminary Events And Vocalizations

Fine cracks appear at large end of Snowy Plover eggs up to 8 d before hatching; chicks are easily heard tapping against shell 3–4 d before hatching, and peeping 1–2 d before hatching (JSW and JCW). There is considerable calling back and forth between the chick and the adult a day or more before hatching (J. Erbes in litt.).

Shell-Breaking And Emergence

Distinct hole usually is not present >4 h before chick emergence (Boyd 1972). Snowy Plover eggs hatch at any time of day and at night. Interval between first and third egg was 1–33 h (n= 28) at closely monitored California nests; 43% hatched in <6 h (Warriner et al. 1986). Average interval for 3 eggs was 14 h at 7 Kansas nests; no relation between laying and hatching order of eggs (Boyd 1972, JSW and JCW). The clutch hatching interval in Kentish Plovers extends up to 72 hrs (Fraga and Amat 1996).

Parental Assistance And Disposal Of Eggshells

Parents run or fly up to a few hundred meters from nest with empty eggshells in their bills before dropping them (Boyd 1972, JSW and JCW). There are usually 1-4 mm eggshell fragments with partly adhering white membranes in the linings of successful nests; their presence is a good way to verify the success of a nest (Mabee 1997).

Young Birds

Condition At Hatching

Precocial; upperparts of Snowy Plovers are pale buff or creamy buff mixed with light gray. Crown, back, rump, and wings distinctly spotted with brown and black; underparts pure white. Distinct white band encircles neck, black line extends behind eye (Boyd 1972). Bill black and legs and legs gray to pinkish-gray. Egg tooth lost within 2 d after hatching. Weight at hatching averages 6.1 g (range 4.6–7.6, n= 504; JSW and JCW). Legs are close to adult size, but wings (mean length = 10.5 mm, range 9–12, n= 4; Boyd 1972), tail (just down), and bill (mean length, from feathers at base to tip of upper mandible = 7.0 mm, range 6.9–7.1, n= 3; JSW and JCW) are much smaller than adult size.

Weight at hatching of Kentish Plover chicks in southern Spain averaged 6.33 g ± 0.56 SD (range 5.3 -7.6, n= 47) and was 64.0%-73.8% of egg mass (Fraga and Amat 1996); egg mass averaged 5.7 g ± 0.4 SD (n= 14) in Hungary (Székely 1990).

At a saline lake in Spain there was a significant positive relationship between Kentish Plover chick mass at hatching and egg volume. Within clutches, heavier chicks hatched from larger eggs, survived better, and recruited into the breeding population in larger numbers than their lighter siblings, but there was no significant relationship between the structural size of chicks and their mass at hatching or between the size of eggs and the sex of chicks. These data suggest chicks from larger eggs may have greater fat reserves than those from smaller ones (Amat et al. 2001 a, b).

Growth And Development

Limited information. In Snowy Plovers, mass increases from average of about 6 g at hatching to 30 g by age of first flight (31 d); wing length increases from about 10 to 85 mm over the same period (Boyd 1972). In California, mass at 4 d is 5.8 g; 8 d, 8.9; 12 d, 11.5; 17 d, 17.5; 20 d, 24.5; 24 d, 25.0; 28 d, 26.4 (n= 1 to 4; JSW and JCW). Up to 4 d of age, only obvious development is an increase in body size and first appearance of pin feathers in primaries. By 7 d, pin feathers are prominent in primaries, secondaries, scapulars, upper back, and along sides; and by 10 d, feathers are breaking from sheathes on crown, scapulars, neck, and sides (Boyd 1972). Juvenal primaries and secondaries are still growing and down is still apparent on head when birds begin flying at about 1 mo of age.

Kentish Plover chicks lost weight during the first 2 d after hatching in Hungary. By the 3rd d weight increased approximately linearly with age and was approximately 2.83 + 1.15 age (Székely 1990). In Spain, the growth rate of chicks was 0.105 g/d per gram of body mass (Fraga and Amat 1996).

During daytime Snowy Plover young first leave nest 1–3 h after hatching (Boyd 1972), stumbling as they walk and pecking at (and presumably eating) potential food on ground (JSW and JCW). Subsequently they make longer, increasingly frequent foraging trips, up to 100 m from nest. In or out of nest, they flatten themselves on ground when parent signals approach of people or potential predators. Chicks leave nest permanently within hours after last chick hatches. They walk, run, and swim well and forage unassisted by parents, but require periodic brooding for many days after hatching. Undisturbed chicks are either nonvocal or too quiet to be heard at any distance. Frightened chicks peep loudly while running to escape danger. As chicks age they are brooded less and for shorter durations (Colwell et al. 2007a); on the northern California coast chicks <10 d are brooded an average of 58% ± 25% SD of the time and chicks that fledge are brooded less than those that die. Brooding bouts average 4 min. Chicks >10 days old were brooded for 17% ± 24% SD of the time. By 10 days of age there was a 90% chance that chicks approached by humans would run whereas chicks approached by avian predators would crouch regardless of age (Colwell et al. 2007a).

First flight of Snowy Plovers is 28–33 d (mean = 30.9, n= 22) after hatching (Warriner et al. 1986). First flight of Kentish Plovers is about 28-30 d of age (Fraga and Amat 1996, Székely and Cuthill 1999).

Parental Care

Snowy Plover adults do not feed their chicks, although they lead them to suitable feeding areas. Adults brood chicks and act as sentinels, warning chicks of approaching predators with alarm calls. They employ distraction displays to confront predators near their broods (see Behavior: predation) and lead larger chicks away from predators. Adults also chase and fight other plovers that come too close to their broods, including pecking chicks of intruding broods (JSW, JSW). Additionally, Kentish Plovers in southern Spain employ aerial pursuits of Gull-billed Terns (Sterna nilotica), closely tracking tern maneuvers, making alarm calls, and effectively driving the terns away (Fraga and Amat 1996, Amat et al. 1999c). Similar behavior has not been observed in Snowy Plovers in coastal California where newly established Gull-billed Terns have recently been recorded preying on plover chicks (R. Patton in litt.)

In w. North America, Snowy Plover females generally desert broods by 6 d after hatching, leaving males in sole care of young; males stay with young until they are 29–47 d old (Warriner et al.1986, Paton 1995). In some cases involving a male’s desertion or death, the female typically rears young alone (Warriner et. al. 1986). On the Pacific coast, females stay with their mates and broods longer when it is apparently too late to nest again (M. Stern pers. comm., J. Erbes in litt.). Late in the season, when lengthy hatching periods are more common, some females continue to incubate unhatched eggs, while the male attends newly-hatched chick(s) away from nest. Also, the female will sometimes stay with the younger chick(s), while the male attends older chicks farther from the nest. Usually the brood reunites and one parent eventually abandons it (J. Erbes in litt.).

On Great Plains and Gulf Coast, both sexes often stay with chicks until they fly; if one sex deserts first, it is typically female (Boyd 1972, Chase and Gore 1989, Chase 1991).

Kentish Plover females also desert broods more than males. Of 101 broods in s. Spain, 14% were deserted by males, 84% by females, and 2% were attended by both parents until fledging. There was no difference in age of chicks when males and females deserted but there was a significant difference between years: 21 d in 1994 versus 7 d in 1996; the duration of biparental care seemed to be directly related to predation pressure by Gull-billed Terns (Amat et al. 1999c). In Hungary, females deserted broods when chicks averaged 6 d of age but timing was highly variable and unrelated to the mass or condition of females; 6% of females stayed with the brood, 27% deserted at hatching, and the rest deserted between hatching and fledging; females stayed longer with late broods (Székely and Williams 1994).

One parent has been removed from Kentish Plover broods to experimentally compare the brood-rearing ability of single birds versus pairs, and males versus females. At Algarve, Portugal, chicks tended by males survived longer than those reared by females (Székely 1996); at Tuzla Turkey, chick survival was lower in broods attended by one than by two parents at one site but not at another (Székely and Cuthill 1999); while single males spent more time brooding their young than males with mates, females displayed a similar tendency at only one of two sites. There were no sexual differences in time spent brooding, adult alert times, or time spent defending young from conspecifics in single-parent broods. It is hypothesized that biparental care may be more successful whenever mortality of young is high from predation or infanticide (Székely and Cuthill 1999).

Kentish Plover broods were experimentally increased and decreased at Tuzla, Turkey to compare the ability of plovers to raise broods of different size (Székely and Cuthill 2000); all young fledged in only 1 of 6 five-chick broods, only 1 of 8 four-chick broods, 4 of 8 two-chick broods, and 7 of 8 one-chick broods. Growth of chicks was not affected by brood size.

Cooperative Breeding

Rare observations of larger-than-normal Snowy Plover clutches with 2 females in attendance (Warriner et al. 1986) indicate that 2 females may rarely lay in same nest. Chick adoption occurs infrequently, usually when 1 parent with chicks cares for ≥1 chicks from another’s brood (Warriner et al. 1986, Himes et al. 2006, M. Stern pers. comm.). Chick adoption has been observed to be initiated after two adults with broods fight for a long period of time, ultimately separating with one chick mixed into the other’s brood. This can result in four-chick broods or chicks exchanged into each brood (D. George in litt.). In one atypical case, a banded male deserted his first (ever) clutch before hatching and cared for 1 chick from a neighboring male’s brood for about 3 wk until the chick fledged (JSW and JCW).

Brood Parasitism

Rare instances of 4-6 egg clutches attended by one female may represent brood parasitism. See Behavior: egg laying.

Immature Stage

No information.

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