Breeding

Phenology

Pair Formation

Mostly Feb–Oct but can occur throughout the year on southern end of range (Peters 1961). Temporal patterns vary with geographic region, with shorter duration farther north. Peak is generally in late spring–early summer (Sayre and Silvy 1993). Pair bonds may persist through entire nesting season and through winter (Mackey 1965), or may change between each nesting cycle (JHS). General activity stimulated by increasing day length (Cole 1933), with more subtle fine-tuning related to latitude and regional/local weather regimes (particularly nighttime temperature). Bond formation confirmed by decreases in frequency of perch-cooing and flapping-gliding flights of male (Jackson and Baskett 1964).

Nest Building

Simple platform nest is constructed in 2-4 days on average and may be further reduced by frequent reuse of existing mourning dove nests as well as nests of other birds. May also nest on small depressions directly on the ground (Drobney et al. 1998).

First Brood

Initiation of nesting generally occurs late Feb–early Mar at southern latitudes, although nests have been found in all months of the year; onset is 1–2 mo later at more northernly latitudes (Fig. 7). Squabs hatch 14 d after laying and normally fledge 12-15 d after hatching. Male parent continues to care for young approximately 12 d postfledging (Hitchcock and Mirarchi 1984).

Later Broods

Interval between completion of one clutch and initiation of next depends on fate of first clutch (Hanson and Kossack 1963). Approximately 30 d are necessary between initiation of successful clutch and initiation of subsequent clutch. Eggs may even be laid in same nest or another nest while young from previous nest are still being tended. After a failed nesting attempt, relaying interval differs depending on age at which original nest was lost. Hanson and Kossack (1963) found most frequent interval for captive birds was 6-9 days; however birds that lost young during the nestling stage had a longer renesting interval, likely due to physiological state of adults while feeding young (i.e., high prolactin levels and crop milk production). The species has a suite of adaptations (small nests, reuse of old nests, small eggs, reduced crop-milk production by females, fast nestling growth, early fledging, clutch/brood overlap) that conserve time and energy, allowing nesting cycles to be 22% shorter than predicted by body mass, and promote multiple brooding (Blockstein and Westmoreland 1993). Average number of nesting attempts within a breeding season appears to decrease across increasing latitudes. Overall duration of breeding season is greatest in southeastern part of the range (80% of nests initiated between 1 April to 26 August) and shortest in western and n.-central part of the range (13 May to 10 August, and 23 May and 25 August, respectively; Geissler et al. 1987). Although continuous monitoring of pairs within a season has been limited, six nesting attempts were observed for a single marked pair in Texas (Swank 1955b).

Nest Site

Selection Process And Site Characteristics

Male initiates selection by inspecting potential sites and uses nest-soliciting call (see Sounds: songs and calls) and wing-flicking to attract female. Nest primarily at woodland or grassland edge, usually in trees but readily on ground in absence of suitable trees or shrubs (Eng 1986, Drobney et al. 1998). Site characteristics are as varied as habitat types used. Use a variety of coniferous and deciduous trees, shrubs, vines, human-made structures, and will also nest on ground. Height of nest varies from ground to 80+ m. Heavy use is made of conifers and orchard trees in East; shelterbelts, mesquite, and ground in central North America; and cottonwoods, mesquite, saltcedar, orchards, grapevines, palms, and ground in West (Sayre and Silvy 1993). Microhabitat characteristics vary, but usually include a flat substrate for platform and some type of surrounding cover. Use of conifers is greater early in nesting season; use of deciduous trees increases as leaves appear. May nest near humans and may use unusual human-made substrates for nest sites (e.g., rain spouts, mops hanging on walls, immobile car accessories; Sayre and Silvy 1993).

Nest

Construction Process

Once nest site is chosen, male selects small twigs, etc., and delivers them to the female while standing on her back (Fig. 8). She arranges them around her while using her body to form simple bowl (Nice 1922). Male may make 30–40 trips to nest site in given bout, which normally occurs in early morning, although occasionally in late afternoon (Jackson and Baskett 1964). Nest-building usually takes 7–10 h spread over 2–4 d (Blockstein 1986a). Nest materials include pine needles, small twigs, grass stems, etc. Nest usually flimsy, often little more than a platform to hold eggs and young; has little insulation value. Pairs occasionally re-use their own nests or those of other Mourning Doves, and also may build nests atop those of other species, particularly American Robin, Common Grackle (Quiscalus quiscula), or Blue Jay (McClure 1943). Males may continue to deliver nesting material to females after onset of incubation.

Eggs

Shape And Size

Short subelliptical to elliptical. Eggs are normally 2.6–3.0 cm long and 2.1–2.3 cm wide (Mirarchi 1993b). Longest egg reported was 4.00 cm (Hanson and Kossack 1963). For captive breeding birds in Illinois, second egg of each clutch was longer and wider than first, and measurements of both eggs of second clutch were larger than those of first (Hanson and Kossack 1963). Egg mass also increased within nesting seasons for birds in Nebraska (Holcomb and Jaeger 1978). Egg mass averages 6–7 g at laying (Holcomb and Jaeger 1978), or 5–6% of female body mass.

Eggshell Thickness

0.11–0.17 mm (Kreitzer 1971).

Color

White, no markings.

Egg-Laying

Determinate layer. First egg is usually laid within 2 d of nest completion, often in early morning. Second egg is laid on consecutive days (12–24 h apart), or alternate days (24–48 h apart). If eggs are removed immediately after laying, female can relay in 5–6 d; if nest is destroyed early in brooding, female may not recycle for 2–3 wk. First egg is not replaced if lost or infertile. Clutch size is normally 2 eggs; reports of 3–4, which have been attributed to “dump nesting” by other females, are not uncommon (Weeks 1980).

Embryo Development

Detailed descriptions of embryonic measurements and development found in Muller et al. (1984) and summarized here. Embryo development slow during first 3 d of incubation; by day 2 embryo apparent as vascularization on yolk sac; day 3: C-shaped embryo with somites, brain, and pigmented optic cups all distinct, limb buds visible under magnification; maxilla and mandible differentiated by day 4; between day 6 and 8 wing and leg buds grow to form distinctly sectioned limbs. Day 9: nares and egg teeth formed on bill; eyelid nearly closed and auditory opening beginning to form. Day 11: Down apparent, especially on head and back. Day 12: scales on legs become evident. Day 14-15: embryo hatches.

Incubation

If clutches are laid on alternate days, little incubation occurs until second egg is laid, while if both eggs are laid on same day or successive days, incubation begins immediately (Hanson and Kossack 1963). Neither parent develops brood patch (Maridon and Holcomb 1971). Incubation period lasts 14 d. Eggs constantly covered, with male and female sharing incubation responsibilities. Male generally incubates from midmorning until late afternoon, female during remainder of 24-h period. Timing of nest exchange can vary by 2–3 h. Female may issue nest call while incubating and upon approach of male, resulting in nest exchange (R. R. Hitchcock pers. comm.), however, no other obvious interchange occurs between mates during exchanges. In desert regions, where eggs can quickly overheat, parents rely on transfer of excess heat from egg to adult where it is subsequently dissipated by evaporative cooling (panting) (Walsberg and Voss-Roberts 1983). Eggshell conductance is not adjusted to cope with humidity shifts, nor is egg dehydration prevented by parents controlling nest humidity (Walsberg 1985).

Intensity of nest defense displays increases throughout the nesting cycle. The probability of a high intensity display, which involve adults feigning injury and often displaying on the ground within 10-20 m of nest, peaks after hatching (Westmoreland 1989).

Hatching

Preliminary Events And Vocalizations

No vocalizations during hatching are described for Mourning Doves.

Shell-Breaking And Emergence

Squabs pip widest end of egg and completely encircle in 15–20 h (Luther 1979). Interval between hatch for two eggs is generally from 12 h to 48 h.

Parental Assistance And Disposal Of Eggshells

No obvious help during hatch from parents. Either parent will dispose of shells, although female usually does because of length of time she incubates. Two trips are made per egg with parent flying out of sight of nest while carrying each half of shell in bill (Luther 1979).

Young Birds

Condition At Hatching

Altricial. At hatch nestlings have closed eyes; head and body are covered with sparse cream-colored (Smithe #54) down. Young are unable to thermoregulate. Prominent white egg teeth are present on both mandibles. The bill, feet, legs, and bare areas around eyes tend to be dark neutral gray (83). Head is barely held upright.

Growth And Development

Detailed pictorial accounts exist for growth and development (Hanson and Kossack 1963) and plumage refinement (Hanson and Kossack 1957b). Descriptions are briefly outlined here. Nestlings grow rapidly: 5 g at hatching, 45-60 g at 10 d, 50-80 g at fledging (12-15 d). Total length increases from 65 to 150-180 mm during first 15 d post-hatching. Growth and development fastest among first-hatched and single squabs; those raised early and late in nesting season grow more slowly than those in middle (Holcomb and Jaeger 1978). Days 2–3: eyes closed; egg teeth present; primary feather sheaths developing on wings. Days 4–5: eyes partially open; egg teeth present; sheaths of secondary wing feathers prominent. Days 6–7: eyes fully open; egg teeth fading; feather tips emerging from primary sheaths; squabs can crawl and/or raise wings over back in defensive posture. Days 8–9: egg tooth present on lower mandible; upper breast well feathered; crown feathers beginning to appear; older nestling may leave nest when alarmed. Days 10–11: feathers at junction of back and neck remain sheathed, belly feathers begin to unsheathe; nestlings readily leave nest when alarmed. Days 12–15: completion of feather coverage under wings and on belly and refinement of feather coverage elsewhere. Plumage is mixture of dark grays, black, and browns; darker and more mottled in appearance than adult birds, possibly to minimize detection by predators on ground in “reference areas” (sites on ground and in trees [often on specific limbs] characterized by dense overhead cover and interspersed with openings; facilitate parent/young feeding interactions [Grand and Mirarchi 1988]) after fledging (Mirarchi 1993b).

Vocalizations consist of weak “peeping” early on, becoming stronger and more persistent as squabs grow, particularly when begging food from parents. Feedings often frenzied, consisting of peeping, wing-flapping, and nuzzling of parents. Beginning on 5th day of feeding, parents (particularly male) will perch-coo to nestlings immediately before feeding; this apparently conditions nestlings to recognize song of male parent, which aids male in locating young for feeding after they fledge (Hitchcock et al. 1989). Begging intensity increases in late brooding period; in captive birds, begging behaviors peak in the week after fledging.

Movements and activities minimal until 7–8 d old. Comfort movements begin then. Maturation of comfort movements occurs at 9–12 d, at which time nestlings are capable of recognizing voice of male parent (Hitchcock et al. 1989). By 13–15 d, nestlings explore immediate vicinity of nest on foot and begin exercising wings.

Squabs < 6 d old are ectothermic (unable to maintain body temperature without brooding); homeothermy still incomplete by 12 d. Complete homeothermy attained at 15 d when body surface/volume ratio has sufficiently decreased and insulative feather coat are present (Breitenbach and Baskett 1967).

Parental Care

Brooding

Constant until 4–5 d; male midmorning to late afternoon, female all other times. By 6–7 d, constant brooding is unusual and squabs may be left unattended for long periods in good weather (Luther 1979). Night brooding discontinued at 9–10 d. Will brood on ground when necessary if young fledge early (Willoughby and Krebs 1986). Female contributes most time, but both parents decrease behavior dramatically at 12–15 d. Changes in brooding behavior correspond with attainment of temperature regulation capabilities in squabs (Mirarchi 1993a). No described nest-relief ceremony. Nest-guarding more casual early in period.

Feeding

Squabs fed by regurgitation (Fig. 9 Mirarchi 1993c). Both squabs usually fed equal amounts, often at same time by inserting bills in each side of parent’s mouth. Feedings may last for several consecutive minutes and may occur intermittently over period of 1 h (Lewis 1993). Both parents feed primarily crop milk for first 3–4 d posthatching, with more seeds substituted for decreasing crop milk by 5–6 d until diet of regurgitated foods is essentially same as that of parents by time of fledging (Lewis 1993). Female feeds more than male 4–15 d posthatching, but feeding responsibilities begin to shift toward male at 12 d posthatching. Male feeds fledglings almost entirely alone for 12 d after they leave nest, while female recycles for next egg-laying. Constituents of Mourning Dove crop milk are unknown but probably similar to that of other columbids, i.e., primarily water, protein, fat, and minerals; no carbohydrates (Mirarchi 1993c).

Nest Sanitation

Fecal pellets are not in a sac and are eaten by parents early in brooding. Parents may also occasionally stimulate defecation (Luther 1979). Care eventually lags later in nestling stage after which droppings accumulate on edge of nest. Reingestion early in brooding may be beneficial to parents because of demands of feeding crop milk (Mirarchi 1993c). Invertebrate nest associates include the mite Ornithonyssus sylviarum (Conti 1993), which does not appear to affect nesting (McClure 1943).

Cooperative Breeding

Helpers

Conspecific helpers reported during nestling stage (Blockstein 1986b); such behavior also reported between Mourning Doves and other doves in captivity and the wild (Neff 1945). Surrogate feeding after young leave nest occurs but is minor. In addition, adoptive behavior of fledglings by adult males may also occur in reference areas (Hitchcock and Mirarchi 1985). Usually includes male’s fledglings and fledglings older than his own. Typically occurs where reference areas of 2 or more sibling pairs are in close proximity or abut congregation sites of immatures. Low frequency of surrogate feedings suggests they are incidental to normal feeding interactions. Seemingly “helpful” behavior is probably a result of misdirected parental behavior rather than reproductive “strategy” (Mirarchi 1993a).

Brood Parasitism

None reported, except occasional “dump nesting” by conspecifics (Weeks 1980).

Fledgling Stage

Departure From Nest

Normally at 13-15 d, as early as 9–10 d if frightened. Preceded by a few days of wing exercises. Young often leave nest for first time during exercise or while begging food from parent. Usually remain in same tree or nearby on ground immediately after fledging (Grand and Mirarchi 1988); may return to roost on nest with parents for 1–2 nights after fledging. Fully feathered except for fine feathering under wings and lengthening of tail; mass about 80 g at nest departure, or 60–65% of adult mass (McClure 1943). Associate with siblings in reference areas for 12–15 d postfledging, where fed by male parent for decreasing periods until 30 d old; thereafter join flocks of immatures. Will remain relatively immobile in reference areas during this period, but will fly to roost trees with sibling each night (and male parent first few nights) and return to reference areas next morning. Can survive without parental care by 21 d old if food sources are nearby.

Immature Stage

Local Movements And Departure Of Fledglings From Nest (15–30 days old)

Most intensive study conducted in mixed pine/upland hardwoods of Alabama (Hitchcock and Mirarchi 1984, 1986, Grand and Mirarchi 1988). There, fledglings left nest and loafed in reference areas on ground or in trees within 45 m of nest tree until 27 d old. Fledglings established new reference areas farther from nest tree as they grew older and flight improved. Fledglings < 21 d old rarely moved > 70 m unless disturbed; maximum distance moved at this age was about 260 m. Movements > 70 m were achieved by several short flights. If fledglings were forced from reference areas at this age, they always returned within 24 h. By 24 d old, some fledglings leave reference areas if abundant food sources are nearby. By this time can fly as much as 345 m at 1 time, although still unable to keep up with adults and older immatures. Fledglings move greater distances when 27–30 d old, at which time they leave reference areas and begin to associate with flocks of immatures up to approximately 1,500 m from nest. During period of fledgling dependency on parents (15–27 d posthatching), maximum movements each day usually are to roost sites, which are changed frequently. Greatest activity takes place in early mornings and late evenings as fledglings move to and from roosts. During remainder of day, young loaf in reference areas where they preen, nap, and peck at potential food items while awaiting parental feedings. Apparently learn to feed by trial and error while in reference areas. Final refinement in feeding probably occurs when fledglings follow male parents from reference areas to foraging areas and observe them and other Mourning Doves feeding.

Local Movements And Behaviors Of Immature Doves (30–160 days old)

Most intensive information collected in Alabama (Losito et al. 1990, Losito and Mirarchi 1991). Daily home ranges and maximum distance traveled between any 2 locations did not vary between sexes, older and younger immatures, or between hunting and nonhunting seasons. Daily home ranges varied from 50 to 1,200 ha, averaged 218 ha. Maximum distance traveled between any 2 locations varied from 1 to 8 km, averaged 3.4 km. Total linear distance traveled by 5 birds followed continuously for 1 d varied from 4.7 to 17.8 km, averaged 8.9 km.

Apparently prior to any migrational movements, immatures range only as far as necessary to find food, water, and shelter. These needs appear to be satisfied in as little as 200 ha on a daily basis and about 2,500 ha over a 1- to 2-mo period. Immatures will fly as much as 18 km in a day and 4–5 km in 1 flight to satisfy those needs.

During summer in Alabama, immatures spent 20% of daily time budget feeding (included searching, procuring, and handling food and grit, drinking, and pecking at bark). Most feeding time was spent in searching (42%) and procuring and handling (53%). Feeding was greatest during morning and late afternoon; occurred primarily in upland fields and residential areas. Directional movement comprised 13% of summer time budget, of which 62% was spent flying, 32% walking, 4% running, and 2% jumping. Preening (comfort movements, including bathing) very important to immatures; comprised second-highest proportion (23%) of daily time budget during summer. Wings, breast, and back preened most often, followed by tail, neck, flanks, rump, and feet.

Immatures spent 21% of diurnal time budget resting during summer. Resting generally peaked during midafternoon, with loafing most common (97%) followed by sleeping (3%). While on roost during summer, immatures did not sleep for long periods (35%), choosing instead to loaf (35%) and catnap (17%). Immatures spent most of summer daily time budget in vigilant activities (24%). These activities included neck twitching, assuming alert postures, pausing and neck stretching, followed by head tilting, head pumping, head bobbing, and preflight crouching. Agonistic activities comprised < 1% of daily time budgets in summer; generally this behavior was greatest in morning and was associated with foraging.