SPECIES

Purple Martin Progne subis Scientific name definitions

Charles R. Brown, Daniel A. Airola, and Scott Tarof
Version: 2.0 — Published September 10, 2021

Breeding

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Phenology

Pair Formation

Coincides usually with establishment of nest-cavity ownership by both sexes. Since females usually arrive at breeding sites later than adult males, some territorial males who control nest cavities remain unpaired for up to 3 wk after their arrival (CRB). In northern Texas, most adults have formed pairs by mid to late April and most yearlings by mid to late May; the latest a pair became established was 5 June (CRB). For representative arrival dates, see Movements and Migration: Timing and Routes of Migration. Birds of both sexes probably spend several days to a week or more investigating nest sites after arrival and before becoming firmly established at a site or choosing a mate.

Nest Building

In the southern United States, may not begin until several weeks after pair formation; the delay is probably a consequence of early spring arrival (20, 266, 267). In n. Texas, nests are seldom started before 15 March and usually not before 25 March (CRB); in Michigan, nest-building begins 2–7 May (20). The interval between arrival and nest-building declines later in the spring, and some yearlings begin nest-building 1–2 d after establishing nest-site ownership (CRB). The time taken to build a nest varies depending on when in the season a pair becomes established. In n. Texas, earlier-arriving pairs spend up to 4 wk building nest before laying first egg; later pairs spend as little as 10 d (CRB). Nest building by birds in central California begins in early May, about 6 wk after the first birds arrive (94).

First Brood Per Season

Figure 2. Usually single-brooded, although martins will produce a replacement clutch if a nest fails in the early part of the breeding season. Egg-laying has been recorded as early as 26 March in Florida (149), 6 April (modal dates 22 April, 1 May) in northern Texas (CRB), 20 April in Alabama (268), 3 May in Baja California (149) and Virginia (269), 8 May in Oklahoma (270), 11 May (modal date 5 June) in Kansas (271), 12 May (modal date 9 June) in Pennsylvania (272), 15–26 May in Oregon (273), late May to mid-June in British Columbia (52), 28 May (modal dates 19–20 June) in Alberta (274), and approximately 10 June in Canadian Maritime Provinces (275). Latest first-clutch initiation dates are 20 June in northern Texas (CRB) and Kansas (271), 8 July in Alberta (274), 15 July in Illinois (168) and Maritimes (275), 17 July in Pennsylvania (272), and 10 August in Maryland (K. Klimkiewicz, personal communication).

Second Brood Per Season

Reported by various authors to be double or triple-brooded, but these reports are not credible in the absence of banded birds (20). True double-broodedness (second laying by birds that successfully fledged young earlier in same season) occurs rarely in southern United States; reliably reported only in northern Texas (220, 221), where first egg dates of 8 second broods were recorded from 13–29 June.

Nest Site

Selection Process

Both sexes visit multiple nest cavities, sometimes separated by at least 0.5 km (CRB), before confining their activity to one cavity or (in birdhouse) a cluster of cavities. It is unknown how long birds generally spend assessing sites (probably longer earlier in the season); choice is constrained by the number of earlier settlers that may control access to cavities (see Behavior: Agonistic Behavior). Females often seem more interested in cavities attended by unpaired males, but some females occasionally take over cavities unclaimed by males (CRB), so they must use cues besides the presence of a male. Females probably spend longer assessing sites before settling than do males. When given a choice, birds often seem to prefer compartments located higher in birdhouses; early arrivals more vigorously defend, and usually later nest in, the upper compartments (147, CRB).

Microhabitat

Nearly 100% of eastern Purple Martin (subspecies subis) build their nests inside cavities in birdhouses or in natural or artificial gourds (239, 276). Martins sometimes use traffic lights, street lamps, or other artificial structures that provide a crack or enclosed cavity. Western Purple Martin (subspecies arboricola) use cavities in dead trees, nest boxes or gourds, crevices in buildings or rocky cliffs, utility poles, enclosed chambers of elevated freeways and overpasses ("bridges"), and even niches in underground lava tubes (50, 51, 104, 52, 103). Southwestern Purple Martin (subspecies hesperia) nest primarily in saguaro cactus (Carnegiea gigantea) (13), but also use rock crevices and cliffs (35). The nest often fills the available space, except when the nest chamber is quite large (e.g., the 5 m × 15 m chambers in bridges), and may be of various shapes depending on cavity configuration.

Site Characteristics

Birdhouses vary widely in style, design, and, to lesser degree, placement. Most are constructed of wood or aluminum; most have 8–12 rooms (range 1–620); and most are placed in relatively open areas away from tree limbs or foliage. In eastern North America, a survey of people with martin houses (239) revealed that 44.1% of compartments in wooden houses were occupied (n = 5,379 compartments), versus 40.6% in aluminum houses (n = 2,946 compartments). Most martin houses are mounted on poles: 62.4% of active colonies were 3–5 m off the ground. Although aluminum houses have several management advantages over wooden ones (see Conservation and Management: Management), many available birdhouses are wooden: 84.2% of houses studied in Minnesota (n = 297; 277). Purple Martin prefers larger compartments and deeper ones (entrance hole higher above floor) than those of most commercially available houses; deeper cavities increase reproductive success (278). Aluminum houses are touted as superior to wooden ones (184), but wooden houses buffer temperature extremes more effectively, and martins have equal reproductive success in aluminum and suitable wooden houses (279). See Jackson and Tate (239) for further details on nest-site preferences, although reported occupancy rates by amateur enthusiasts are often unreliable.

Hollowed-out gourds are also used as nest sites, commonly in the southeastern United States and less so elsewhere. Each gourd is a single cavity and has advantages over multicompartment birdhouses: a gourd's cavity is deeper and often larger. Multiple gourds are usually erected, strung on wires from poles. Plastic gourd nesting sites are now available. In the southeastern United States, birds may prefer gourds over birdhouses. Early naturalists reported Native Americans erecting gourds for Purple Martin; thus, the birds began their shift to artificial nest sites before the colonization of North America by European settlers (196). As early as 1712, Purple Martins occupied gourds in the Carolinas and Florida (280). Use of multi-compartment birdhouses is restricted mostly to the eastern populations.

Most birdhouses used in the West are single-cavity houses, such as those erected for bluebirds and Tree Swallow (Tachycineta bicolor) (281, 282) and more recently wooden boxes and plastic gourds specifically designed for the Purple Martin. In Pacific populations, the proportion of nests in nest boxes and gourds varies from nearly 100% in British Columbia (52), 90% in Washington (50), 50% in Oregon (283 ,102), and < 1% in California (51, 103). Use of boxes, gourds, or other artificial sites has not been reported in other parts of the range of subspecies arboricola or hesperia. Western Purple Martin has occupied traditional multi-compartment boxes and gourd racks near the Columbia River in Washington and Oregon (283), with 110 pairs nesting in a backyard setting in Washington (284), indicating the capability for rapid adjustment to novel nesting situations.

Purple Martin has been reported to use cracks and crevices in buildings throughout their range (e.g., 285, 286, 100, 287, 103). Subspecies arboricola mostly abandoned these types of sites in many areas after the arrival of the European Starling (Sturnus vulgaris) (101, 50, 52). Subspecies subis shifted away from use of buildings as more birdhouses and gourds have been installed in eastern United States. Occasionally martins use other artificial structures: traffic lights and civil defense sirens (CRB), a crack in the top of a flagpole about 40 m high (149), crevices in pilings underneath piers and docks (286, 282, 283), street lamps (288), holes in moving arms of oil pumps (289), holes in orange aviation warning balls on transmission lines (290), birdhouses erected for other species such as ducks (291), and a gourd attached to the mast of a moving ship (292). There is one report of nesting on the ground in Wisconsin (293).

Natural nest sites are usually woodpecker holes in cacti or dead snags . Since Purple Martin uses cavities excavated by several species (see Behavior: Social and Interspecific Behavior), cavities chosen differ widely in size, depth, entrance hole diameter, height above ground, and position within the tree or cactus. For subspecies hesperia nesting in saguaro cacti in Arizona, mean cavity height was 7.4 m (range 4.7–10.4, n = 49); mean height of the saguaro used was 9.0 m (range 5.1–12.2, n = 49); mean entrance diameter was 7.4 cm (range 5.0–9.0, n = 17); and mean cavity depth was 15.5 cm (range 7.0–24.0, n = 17) (13). For subspecies arboricola nesting in dead trees in Colorado, mean cavity height was 7.7 m (range 3.9–13.1, n = 14); mean diameter of the aspen (Populus) used at the cavity level was 29.8 cm (range 19.8–42.0, n = 14); mean entrance diameter was 5.9 cm (range 4.2–7.7, n = 14); and cavity depth varied from 24.0 to 47.0;108). Most cavities in cacti were within 3 m of the saguaro's stem apex. Mean orientation of saguaro nests was 233°, 67% of cavities faced a southerly or westerly direction (136–315°), and 90% of nest cavities were in the main stem of a saguaro, as opposed to a branch (13). Cavity is often located in a pine or aspen tree; others include Sabal palm, oaks (Quercus), sycamores (Platanus), spruces (Picea), firs (Abies), and cypresses (Cupressus) (149, 100, 229, 108). Nest trees are usually dead, but live ones are occupied if they have holes (86). Nests in southern Oregon were located in moderately decayed snags located > 100 m from forest edges in relatively open sites created by clearcutting (97); those in Colorado were adjacent to open areas such as natural parklands, clearcuts, or powerline right-of-ways, with all nest cavities facing toward the openings (108); and those in western Washington had significantly more open canopy cover than trees with unused cavities (294). Birds nested in rock crevices on islands in lakes in Minnesota through 1930 (231). Subspecies hesperia uses rock crevices on treeless islands in Gulf of California (35) and sandstone cliffs on mainland Baja California (112). Birds nesting in these sites have not been studied, and little is known of their nest-site characteristics.

Bridge sites used in the Central Valley and on the coast of central and northern California include true bridges (over waterways) as well as elevated freeway sections and longer overpasses over dry land. All sites are at least 85 m long with a vertical space of at least 6 m of open airspace beneath them. Sites also are typically adjacent to land that is open, presumably to provide flight access to nest chambers. All nests sites are of box-girder design, in which nesting chambers consist of a series of large "boxes" (1.3 m tall × 5 m wide × 5–20 m long) formed by the bridge structure that are accessed via 15–18 cm diameter air holes ("weep holes") in the undersides of the bridge (101, 94).

Nest

Construction Process

Mostly by the female, except the male frequently collects green leaves for the nest . The male sometimes initiates nest-building, gathering first few twigs or leaves, but once the female begins, the male mostly escorts his mate on her trips to get nesting material or sits near the nest cavity and watches. Birds pick up twigs, coarse grass, dead leaves, pine needles, and mud from the ground, although occasionally they try to break twigs off branches while perched. Gathers most nesting material within 250 m of the nest site in eastern populations, but some birds in northern Texas traveled up to 0.8 km to collect mud (CRB). In urban Sacramento, California, where nesting material can be limited, birds readily pick up grasses and pine needles that humans spread in open areas near nest sites, often retrieving material within minutes of its placement (94).

The nest begins as a loose mat of twigs and grass spread evenly across the floor of the compartment. In most commercial birdhouses with entrance holes 2.5 cm above floor, birds gradually push material up toward the base of the entrance hole to effectively increase cavity depth. Martins use mud to varying degrees; they always place mud at the base of the entrance hole, often creating a mud wall in front of the nest bowl. In deeper cavities, no mud walls are built (278). Within large bridge nest chambers, subspecies arboricola often locates the nest near construction framing, pipes, or large construction debris (255). A video camera mounted inside a compartment (200) showed that both sexes (but especially the female) repeatedly attempt to scratch out a bowl amid the nesting material in a corner of the compartment. They do this by spinning around, and pushing their breasts flat against the floor with the wings spread. When entering a compartment with nesting material, they spin around several times and then, holding the nesting material, vibrate their beak against the substrate for several seconds in a sideways motion before letting go. The female frequently displaces the male when he sits in the nest bowl (200).

Male often puts nesting material in all compartments of his territory and does not confine nest-building activity to the nest cavity until the nest is half built. Female may start by building in several rooms but quickly confines her activity to the chosen compartment.

Both sexes of eastern and western Purple Martins collect fresh green leaves, gathering them by sitting at the apex of a tree branch and picking off pieces. They place green leaves in the nest bowl over and around the eggs (295); when the leaves dry out and curl up, birds may remove them from the nest. Widely reported by many authors, the function of gathering green leaves is unclear; at least seven hypotheses have been offered to explain it (296). In Arizona, subspecies hesperia collects green leaves less frequently, perhaps because fewer are available in the Sonoran Desert; nest-building in desert martins otherwise generally parallels that seen in other populations (13), except the timing is later to coincide with summer monsoon rains.

Nest-building in Purple Martins seems to be determined more by each pair's own breeding phenology than by what other martins do.

Structure and Composition Matter

Nests are built out of twigs, stems of herbaceous plants, leaves, and mud. Miscellaneous items such as aluminum can pull tabs, pieces of bread, or nails are sometimes incorporated into the body of nest. The use of mud varies widely within both eastern and western martins (94), perhaps determined in part by local availability. Some pairs make extensive mud walls that abut the lower part of the entrance hole; other nests in the same colony, especially those built by yearlings, may have no mud at all. Mud is used more often in wet years than in dry ones (224, CRB).

The remainder of the nest is a mat of twigs, grass, or pine needles. The depressed nest bowl usually is positioned toward one side of the compartment. Nest bowl sometimes includes bare floor as the rest of the nest is built up around it. The nest bowl contains green leaves, usually a thick mass that fills the bowl by the time egg-laying begins. Eggs, especially during laying, are often hidden beneath the leaves. The overall amount of nesting material varies; some birds fill a compartment to a depth of several centimeters, others barely cover the floor. Purple Martins sometimes appropriate a compartment that contains a partly built nest of a House Sparrow (Passer domesticus), using grass put in by sparrows as the base for their nest. These nests may contain feathers brought in by sparrows, which martins do not try to discard.

Dimensions

Overall size is determined by size of the cavity; birds usually fill the available space, regardless of size or shape of compartment, except in bridge chambers. The nest bowl usually measures 9–10 cm in diameter, and the entire nest weighs 50–300 g, depending on presence of mud (20).

Microclimate

Little quantitative information. Varies with type of cavity. Birdhouse manufacturers claim that the interior of aluminum houses is cooler in hot summer weather than that of wooden houses (184). However, there is no evidence to evaluate this claim, and wooden houses offer a more suitable microclimate by better buffering ambient temperature extremes. In saguaro cactus, nest cavity is surrounded by several centimeters of moist inner tissue, which insulates the nest from intense summer heat in the desert (297). The substantial mass of the concrete bridges used for nesting by western martins likely ameliorates summer air temperatures that regularly reach 30–40ºC during the breeding season in Sacramento, California (DAA).

Maintenance or Reuse of Nests, Alternate Nests

Commonly reuses the same nest cavities in successive years. In Pennsylvania, birds occupying compartments with old nests fledged more young than did those using clean compartments (298); however, this may not have reflected any benefit of old nests per se but rather the fact that older females who lay larger clutches (see Demography and Populations: Measures of Breeding Activity) are more likely than yearling birds to return early and occupy the old existing nests. In subspecies hesperia of Arizona, 40% of cavities used in one year were active the next year (n = 30; 13). Does not add twigs, grass, or mud to nests once nest-building stops; the only maintenance is to discard dried leaves and gather new green leaves.

Because Purple Martins in birdhouses often maintain territories containing multiple rooms, many pairs have alternate compartments where they roost that can be used for the nest if the first nesting attempt fails or if the nest compartment is appropriated by House Sparrows or European Starlings. Sometimes a pair places the rudiments of a nest (twigs, grass) in these extra compartments when first starting nest construction and before confining nest-building to the chosen room, but no true alternate nest is constructed.

Nonbreeding Nests

None known.

Eggs

Shape

Ovate to elliptical ovate (149).

Size

From the Western Foundation of Vertebrate Zoology (n = 27 clutches, 125 eggs drawn from across species' range). Means and extremes based on clutch averages: length 24.28 mm (range 21.31–26.98), breadth 17.35 mm (range 16.13–18.66), empty shell weight 0.232 g (range 0.189–0.283).

Mass

Mean 4.1 g (range 3.4–4.6); first egg of clutch is the lightest, and each successively laid egg weighs slightly more, varying 0.2–0.6 g from the first to the last egg (20).

Eggshell Thickness

No pre-DDT and post-DDT comparisons available. Empty shell weight (see Mass) is presented for future reference.

Color and Surface Texture

Pure white; not glossy. Surface texture smooth.

Sixty-six different species of bacteria have been identified on the eggshell surfaces, with those of the Gamma-Proteobacteria subphylum the most prevalent; the three most common families within that subphylum were Pseudomonadaceae, Xanthomonoadaceae, and Erwiniaceae (299).

Clutch Size

Mean eggs per nest (n) was 4.6 eggs (335) in northern Texas (300), 4.9 (45) in Missouri (224), 4.2 (33) in Kansas (271), 4.9 (84) in Michigan (20), 4.0 (300) in Maryland (K. Klimkiewicz, personal communication), 4.6 (995) in Pennsylvania (128), 4.8 (104) in Massachusetts (301), 4.8 (54) in Alberta (274), and 4.6–5.2 (7–69) in British Columbia (63, 52). Typical range 3–6 eggs, although clutches of 1–2 and 7–8 have been recorded. Clutch size tends to decline during the summer, largely because yearlings lay fewer eggs and nest later (274, 300; see Demography and Populations: Measures of Breeding Activity). Replacement clutches tend to average 0.5–1.0 eggs fewer than initial clutches (20, 271, 274, CRB). Clutches of 5 second broods in northern Texas contained 2, 4, 4, 5, and 6 eggs, respectively (220, 221). Mean clutch size for subspecies hesperia in Arizona was 3.9 eggs ± 0.7 SD (range 3–5, n = 11) (13).

Egg-Laying

Occurs early in the morning (224, 20, CRB). Video camera inside a New Brunswick martin house (200) revealed that female laid 4 eggs on successive days from 08:00 to 09:11 ADT. During laying, female's breathing looked labored (80 breaths/min), her head was pressed against the wall, her cloaca was in the center of the nest bowl; obvious contractions occurred every 3 s. She arched her back and jerked wildly when the egg came out. After laying, she got off the egg, rolled it with her beak, then sat on it and spun around in the nest bowl. Female did not leave the compartment for almost 2 h after the egg was laid. Her mate later sat on egg, while female perched nearby. At night, female slept sitting on the egg. Female laid an egg while the male was in the compartment sitting on the other egg. Male and female seemed to compete with each other to sit on the eggs.

Egg-laying within a colony is not as synchronized as in the highly colonial swallows; for example, in a northern Texas colony of 35 nests, clutch initiation dates ranged from 6 April to 20 June (CRB), a much greater range than that seen in similarly sized Cliff Swallow colonies (127). Replacement clutches are usually produced if nests fail during the first part of the nesting season. Purple Martins often reuse the same nest for a replacement clutch, especially if the eggs of the first clutch disappear because of depredations by wandering House Sparrows or European Starlings. If a predator gets the eggs, birds are more likely to move to another compartment or abandon the colony site entirely.

Incubation

Onset of Broodiness and Incubation in Relation to Laying

Female may incubate intermittently as soon as each egg is laid, because she often sits on eggs during the laying period (200). By the day the penultimate egg is laid, female spends considerable time in the nest with incubation beginning at least by the evening that the penultimate egg is laid (302).

Incubation Patch

Single medial abdominal patch in females only. Brood patch disappears quickly after breeding (2).

Incubation Period

Usually 15–18 d (224, 20, 274, CRB). Reported range is 12–20 d (224, 149), although recorded durations shorter than 15 d are probably an error, unless birds transport eggs between nests as Cliff Swallows do (127), a behavior that has not been observed in Purple Martin.

Parental Behavior

Female is generally regarded as the incubator, but the male often enters and remains for long periods in the nest cavity during incubation, especially in the female's absence. Male sits on eggs while in the nest (200). The female often has trouble getting the male to get off the eggs upon her return; she nudges him and sometimes tries to crawl under him to get on the eggs (200). Both sexes spin around on eggs frequently while sitting on them. The male stops guarding his mate entirely when incubation begins, and he remains in or perched outside the nest cavity when his mate leaves to forage. the male forages while the female is in the nest; thus, one parent is usually present. However, nests are briefly left unattended relatively often, allowing egg loss to House Sparrow during incubation (CRB).

In Michigan, females incubated about 70% of daylight hours when temperatures were near normal (about 21°C) but increased to 81% when temperatures dropped 6°C. below normal (20). In Ohio, mean percentage of daylight hours incubated was 76.7 with average temperature of 16°C. (S. C. Kendeigh in 20). In western New York, mean attentiveness was 72%, varying from 68 to 79% among nests (302). Bouts of incubation (attentive periods) usually lasted 4–15 min but sometimes > 30 min in cool weather in Michigan. In Ohio, average daily attentive period was 32 min (20). Inattentive periods by females usually lasted 5–12 min (up to 35 min) in Michigan, and averaged 9.3 min in Ohio; males were present in nest cavities during portions of the inattentive periods. Alarm calls cause incubating birds to get off the eggs and peer out the entrance hole. Attentiveness of birds in western New York was affected by ambient temperature, time of day, day of incubation, and calendar date (302).

Hardiness of Eggs Against Temperature Stress; Effect of Egg Neglect

No quantitative information. During cold and rainy weather that lasts 3–4 d or longer, the eggs can become chilled as a result of neglect by adults that spend long periods foraging. Many such eggs do not hatch, and adults consequently abandon the nesting attempt (see Demography and Populations: Causes of Mortality). Egg-chilling is probably worse in aluminum birdhouses.

Hatching

Preliminary Events and Vocalizations

No information.

Shell-Breaking and Emergence

Eggs hatch at all times of the day and night (CRB). A clutch is said to require up to 4 d for all eggs to hatch (224), but most eggs hatch within 24–36 h of each other. In a nest monitored with a hidden video camera, all 4 eggs hatched within 48 h (200).

Parental Assistance and Disposal of Eggshells

Parents are not known to assist in hatching (200). Parents remove the eggshells, carrying them away from the nest site to drop them. Parents usually do not eat the eggshells, despite their apparent use of eggshells as grit and calcium at other times of year (see Diet and Foraging: Diet).

Young Birds

Condition at Hatching

Most young at hatching have no natal down and are reddish pink. Rectrices and remiges are visible beneath the skin—tips protrude about 0.5 mm—and one bird weighed 2.8 g immediately after hatching (20). A small egg tooth is present. Newly hatched young rests on its large abdomen with its head curled around, in same basic position as in the egg. Dangles legs and wings from its sides and uses them for support when begging for food. Sound or touch stimulates a chick to beg, which it does by weakly lifting its head and faintly calling (20). Individuals that hatch early in the morning gain up to 4 g by nightfall of the same day.

Growth and Development

Birds gain mass rapidly; total body mass averages about 10 g (day 3), 20 g (day 6), 30 g (day 8), 40 g (day 10), 50 g (day 13), and peaks at about 60 g (days 17–21). Birds then slowly lose weight, declining to about 50 g by day 28, when most fledge (20, 303). By day 6, a bird can right itself if overturned, and it can keep its eyes open, although it usually does not keep its eyes open until days 9–10. The skin becomes increasingly bluish because of unopened feathers underneath it, but no feathers start to break through until day 12 (20, 303). Rectrices and remiges begin rapid growth; 6th primary (p6) increases from 4 to 70 mm from day 12 to day 20. Remaining feather tracts that start rapid growth on day 14 and are largely complete by day 20 (20).

Nestlings orient toward the entrance hole by day 12 (224), and all brood members cluster together to greet incoming parents. By days 13–14, nestlings turn around to defecate out of the entrance hole. Young start showing fear reactions at days 14–15, crowding to the back of the compartment when parents give alarm calls. By days 15–16, young will return to the compartment if placed on the porch in front of it. Rectrices and remiges continue to lengthen from day 21 to day 28.

Young birds gape when a parent or any other martin passes, and nestlings sit increasingly farther out of the entrance hole as they become older. When large, often only one bird at a time can be in the entrance, and brood members joust among themselves for access to the entrance. When one is fed and presumably satiated, it turns around and goes back into the compartment and another young bird replaces it (CRB). Young exercise by stretching and flapping their wings before fledging, and they preen by at least day 20. In birdhouses equipped with porches below entrance holes, nestlings often come out and sit on porches several days before fledging. Parents feed them on the porches. Young move between compartments that share a common porch; some birds enter adjacent nests. Older nestlings sometimes move into adjacent nests containing younger broods and take food from the smaller nestlings' parents, occasionally causing younger nestlings to starve (304).

Parental Care

Brooding

Begins at hatching and continues with decreasing frequency until day 10 (20). On the day of hatching, the female broods the young about the same amount of time (71% of daylight hours) as she had been spending incubating. Often, a parent spins around on top of the nestlings while brooding them (200). Male does not brood.

Feeding

Begins at hatching and continues until 5–7 days after fledging. Video camera recordings (200) showed that feeding begins within a few hours of hatching; parents may regurgitate food to very small young and move among all nestlings of a brood, feeding each one on a single visit. Feeding increases each day, peaking at about the time of maximum nestling mass gain on days 17–21. Parents sometimes bring prey too large for small young to swallow; they quickly pull the food out of a nestling's mouth if not immediately swallowed.

In a study with feeding trips counted from dawn to dusk on a single day (224), overall average rate of feeding for all pairs was 13.2 food deliveries/brood/h, in line with that seen in a later study (305) and in other swallows (127). Finlay (274) found that for brood sizes of 1–7 nestlings of known ages, frequency of parental visits to the nest increased, peaked, then declined with nestling age in a pattern paralleling that of nestling weight gain. Michael (305) found that young were fed 11.9, 13.2, 8.4, and 6.1 times/h in weeks 1, 2, 3, and 4, respectively. Walsh (177) found that the amount of food delivered per visit increased throughout the nestling period, and the percentage of visits by parents in which they actually delivered food, increased to nearly 100% by day 20. Provisioning rates by parents as a function of age are presented by Williams and DeLeon (306). In western New York, the average number of food deliveries/nest over all nests and nestling ages was 186 (range 43–295) per 15-h day (06:00-21:00 h) and 12.4 deliveries/nest/h (range 0–39) (306). The same study showed that nestling age, temperature, time of day, wind speed, and extent of ectoparasitism affected the number of food deliveries at a nest, with nestling age and temperature having the strongest effects (306).

Both sexes feed the young, with the female doing slightly more than the male: 55.6% of all food deliveries in Missouri (224) and 56% in Arizona (13) were by females. Except for soon after hatching, parents usually feed one nestling per visit and do not apportion food among the brood. Feeding rates by males do not correlate with the extent of mate-guarding they did earlier and thus with their certainty of paternity (217, 307).

Nest Sanitation

Parents eat the fecal sacs until the nestlings are at least 8 days of age; adults assiduously search nest compartment for feces and poke cloacal regions of small nestlings as if stimulating them to defecate (200). After day 8, parents carry fecal sacs away from the nest site, dropping them ≥ 20 m away (CRB). Nestlings defecate on the entrance rim of the nest after about days 13–14; if a fecal sac does not fall clear of the nest cavity, parents pick it up (even if on the porch below the entrance hole) and carry it away. Backing up to the rim of the entrance to defecate may be risky for nestlings, since occasionally they lose their balance and fall out of nest cavity.

Carrying of Young

Not known to occur.

Cooperative Breeding

Not recorded. In rare instances, a bird that loses its mate during nesting is joined by a replacement, and in one case a male replacement helped care for the young (214).

Brood Parasitism by Other Species

No interspecific brood parasites of Purple Martin are known. Occasional reports of Brown-headed Cowbird (Molothrus ater) parasitism (308) are not credible. Eggs of House Sparrow are occasionally found in Purple Martin nests (CRB), probably a consequence of the high density of compartments in birdhouses occupied by both species. Purple Martins are not known to have hatched a House Sparrow egg and raised the young. Nestling White-throated Swift (Aeronautes saxatalis) have been found in nests in California, but it is unclear if the swifts laid eggs in the martin nest or nestling swifts wandered from their nearby nests to the martin nests (255). A young swift was fed in one nest for at least 9 d.

Fledgling Stage

Departure from Nest

Young birds may sit on porches for 1–4 days before fledging. They usually leave the nest in the morning during the first 2 hours of daylight (309). Parents do not try to pull their own young off a porch or out of the nest, contrary to the statement by Allen and Nice (20). Juveniles fly from the nest often just after a parent departs and then follow the parent closely. All young of a brood often do not leave on the same day, and broods of 6 young often take 3 days for all to fledge (309). This asynchrony in fledging, and juveniles' frequent return to the nest after their first flight (see below), has contributed to disagreement about the time that young typically spend in the nest. The nestling period has been reported to last 27–36 days (various authors), but 28–29 days is likely most typical (20, CRB).

Parasite load, ambient air temperature, and type of birdhouse may interact to influence fledging times. In northwestern Pennsylvania, the number of young that fledge averages 3.65 ± 0.05 (n = 905 nests), with the mean fledging date being 15 July. Fledging date is independent of brood size. Fledglings in nests of yearling females fledge later (mean 17 July ± 0.8 d) than fledglings of older females (13 July ± 0.5 d) (128).

At the time of fledging and for several days afterward, juveniles are harassed by non-parental martins, frequently yearling males. Any juvenile flying near a colony may be chased by several birds, all trying to peck it, usually with its parent trying unsuccessfully to drive off the attackers (309). Function of this behavior is unclear (310). The most popular explanation, that it serves to reduce chances that fledglings might enter other nests in the colony with smaller young and steal food (311, 312), cannot hold for the many nonbreeders that engage in juvenile harassment (CRB). At fledging, young generally fly well and can sustain flight for relatively long periods (5–10 min) without perching. Parents and young call frequently during and after fledging.

Association with Parents or Other Young

Perhaps because of harassment from other martins, parents lead the young away from the colony site soon after fledging. Juveniles from a given brood assemble in a relatively fixed area, where they remain for the remainder of the day and often for several days afterward (309). Parents are usually able to assemble their entire broods. Juveniles generally perch on wires, dead tree limbs, TV antennae, or other open substrates where they are easily seen. In a northern Texas colony, 63% of broods (n = 41) were located in assembly areas within 1.6 km of the colony site (309). Juveniles mostly sit together, flying relatively little. Parents are usually nearby and visit juveniles to feed them. Nonparental martins, upon passing a brood, often stop and harass the juveniles, knocking them off their perches and chasing them. As young become better fliers, the entire family vacates the assembly area, usually within 1–5 days, and disappears; one family was found 2.1 km from its assembly area (309). By this time, juveniles are flying more often, and family may not be spatially tied to any single area.

Many broods (n = 35) returned to the nest to sleep each night for several days (mean 4.8 d, range 1–12) after fledging (309). Pairs nesting later in the season are less likely to bring their young back to the nest to sleep. Parents initiate the return by leading the juveniles to the colony, using Choo Calls (see Sounds and Vocal Behavior: Vocalizations). Parents also lead the young back to the nest earlier in the day if weather is stormy. Fledgling western Purple Martins returning to bridge nest sites to roost have difficulty in entering the vertical entrances of bridge nest chambers, which may split up family groups and contribute to low post-fledgling survival (101, 94).

Parents show no ability to recognize their own young and cannot distinguish them from other juveniles of similar age (193). Parents recognize only young that are vastly different in age from their own. When several broods of similar age simultaneously return to nests in the evening to sleep, parents seem to compete to lead any juvenile they encounter back to their nest. As a result, juveniles from different broods often mix, and about 25% of broods in assembly areas contain a juvenile from another brood. Parents feed adopted young as their own. Lack of parent-offspring recognition is a characteristic of swallows that nest solitarily (236).

During the first 2 days after the young leave the nest, parents feed them by alighting beside them. On the third day, the parents often hover above the perched young and drop food into their mouths. On the fourth day, juveniles and parents begin in-flight transfers of food, in which a juvenile flies out to meet an incoming parent. Both birds hover briefly, and either the juvenile seizes the food or the parent drops it and the juvenile catches it. In-flight transfers are common after the fourth day out of the nest, and probably continue until juveniles become independent (309).

Occasionally, parents lead juveniles on apparent foraging flights. Juveniles gape and flutter wings whenever any adult martin approaches. Despite colony sizes sometimes as large as 35 nests in northern Texas, creches of young were never seen (CRB), unlike in more colonial swallows (127). The lack of creches partly reflects more staggered fledging times, but parents also seem to try to avoid assembling their fledged young near another brood. See Brown (309) for further details on post-fledging behavior.

In California, for up to a month after young fledge from bridge nesting sites, adults from multiple colonies bring family groups, including dependent young, up to 7.5 km to a communal evening roost site, where they perch, drink, and pick up grit (160, 94).

Ability to get Around, Feed, and Care for Self

Juveniles begin catching insects on their own on days 4–5 after fledging. They probably become fully independent by 7–10 days after fledging. At that time, adults reappear at the nest site for long periods (309), suggesting that they are no longer caring for young.

Immature Stage

Relatively little information. Juveniles probably travel widely once independent, and join flocks of other Purple Martins. Some continue sleeping in birdhouses, often at non-natal colonies (312). Associations between family members break down after juveniles become independent. Some independent juveniles enter nests that contain smaller young, apparently to steal food (312, 304). Fully grown independent juveniles out of the nest 6–7 weeks return to colonies during morning hours, and some defend cavities (313). These birds sit in compartments and lunge at intruders. Their behavior parallels similar behavior by adults (195), who also return to nest sites (usually their own) after their young fledge and defend their former territories. Apparent juveniles have been seen trying to copulate in late summer (314). Independent juveniles join with birds of older ages in late-summer roosts and spend less time around colony sites as migration draws nearer (see Movements and Migration: Migratory Behavior).

Recommended Citation

Brown, C. R., D. A. Airola, and S. Tarof (2021). Purple Martin (Progne subis), version 2.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.purmar.02