SPECIES

Brown-headed Nuthatch Sitta pusilla Scientific name definitions

Gary L. Slater, John D. Lloyd, James H. Withgott, and Kimberly G. Smith
Version: 1.1 — Published August 18, 2021

Breeding

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Phenology

Pair Formation

Pair bonds can be established at almost any time of year (Cox and Slater 2007). Two juveniles banded together in July were paired the following breeding season. A male attracted a female in mid-April after completing a nest cavity in mid-March. Pair bonds retained over multiple years and likely permanent.

Nest-Building

Cavity excavation recorded in all months, Nov–May, but most frequently in Feb–Mar in southern states and Mar–Apr in northern states (Figure 4).

First Brood Per Season

One of the earliest breeders in Southeastern pine forests. Mean egg date for states in the range is 9 Apr ± 19 d SD; date for N. Carolina (23 Apr) significantly later than dates for Florida, Georgia, and S. Carolina (4–6 Apr; 77). Egg-laying spans 2 mo within each state; 90% of clutches completed by 5 May (77). In s. Florida, mean start incubation 23 March + 16 d SD, range = 16 Feb - 14 May, n = 249 (49, Slater 2001, Slater 2004, Lloyd and Slater 2007). In n. Florida, Clay Co., clutch initiation 27 Feb – 9 Apr, 53% initiated in late March (n = 13, Miller and Jones 1999). In an e. Texas urban population, clutch initiation 22 Feb – 23 March (n = 13, Thompson 2000). In e. Texas pine forest, earliest clutch initiation 22 Feb (n = 22, Dornak et al. 2004). Incubation, lasting mean of 14 d, usually in Apr; young in nest, 18–19 d, Apr–May (see Figure 4).

Reasons for the relatively early nesting phenology of this species remain unclear, although early nesting may minimize exposure to hot weather, competition for cavities (49), or predation by snakes (81).

Second Brood Per Season

Few second broods recorded and likely limited to earliest initial breeders (see Demography and populations: measures of breeding activity, below). Of 2 N. Carolina second broods, 1 hatched 21 May and fledged 10 or 11 Jun; the other hatched 23 May but failed 10 Jun (Norwood and Norwood 79, 86). A successful second brood in Louisiana was begun immediately following the 26 Apr fledging of the initial brood (71). In s. Florida, 5 pairs that attempted second broods had initiated the earliest first broods of the season; 3 had first brood incubation dates <1 Mar (49, Lloyd and Slater 2007). Some Florida breeding records in May and Jun may be second broods (22). In e. Texas, a successful second brood clutch initiation date 11 Apr, first brood 1 Mar (Thompson 2000).

Nest Site

Selection Process

Male takes lead in selecting the nest site (1).

Microhabitat

Snags for nesting occur naturally in southeastern pine forests because of fire (e.g., fire-blackened stumps), in open areas adjacent to pine woods, or in wet pine savanna or ponds because of flooding. Artificial microhabitats used include nest boxes, fence posts, telephone poles, light poles, and wooden pilings in residential or rural areas, as well as clear-cuts in which small snags are retained (66). In all cases, the presence of mature pines within a few hundred meters for foraging is necessary. Occasionally pairs nest in the dead portion of live conifers, live cypress trees with decaying heartwood (49), or deciduous trees (66).

Site Characteristics

Favors well-decayed snags—either pine or hardwood. McNair (77) surveyed museum egg records, literature accounts, individual accounts, and CNRP data, and found that of 12 site categories, 47% of nests were in 1 category: pine stumps. Nest heights are among the lowest of North American cavity nesters: median 1.2 m (range 0.2–27.2, n = 50; Georgia: 1); median 1.5 m, mean 2.09 m ± 1.59 SD (n = 309; throughout range: 77); mean 2.7 m (n = 34) for natural nest sites and mean 1.6 m (n = 23) for fence posts and nest boxes (Louisiana: 71); mean 2.4 m (range 0.75–7.6, n = 7; Texas: 57); mean 2.2 m + 0.2 SE (n = 24; Texas: Dornak et. al. 2004); mean 5.1 m (range 1.7–12.0, n = 13; Arkansas: JHW); and mean 3.15 m ± 1.71 SD for natural nest sites (n = 31) and 2.46 m ± 1.62 SD for nests not in nest boxes (n = 55; throughout range: CNRP). Mean nest height is substantially higher in s. Florida (10.8 m, n = 60), possibly because of the lack of small short snags because they decay rapidly (49).

Mean diameter at breast height (dbh) of nest trees: 27.1 cm (range 13.7–45.7, n = 15; Louisiana: 71); 25.6 cm (range 16.4–43.8, n = 7; Texas: 57); 31.3 cm (n = 24; Texas: Dornak et al 2004); 21.8 cm ± 1.6 SE (n = 34) and 30.5 ± 1.5 (n = 26; Florida: 49); 24.1 cm (range 9.1–49.6, n = 13; Arkansas: JHW). Mean heights of snags used for nesting in 2 different habitats in s. Florida were 11.45 m ± 0.96 SE and 15.31 m ± 0.88 SE (49).

Nesting areas in s. Florida had more large snags (>15 cm dbh) and pines and fewer small pines than random sites (49). In Texas, nest snags were shorter (3.2 m + 0.3 SE) than control snags (12.0 + 1.8 m, n = 24) and nuthatches preferred the top half of the snag (Dornak et al. 2004). They also had less dense mid-stories and less leaf litter than random sites.

Nest

Construction Process

Usually excavates the nest cavity, but sometimes uses an existing cavity of nuthatches or woodpeckers, as well as artificial nest boxes. May begin multiple cavities before choosing one for nesting. In s. Florida, breeding groups excavated 2.35 sites/group, and only 6 of 23 groups that were found excavating before 1 Mar nested in initial site, although no group found after 1 Mar changed sites (49). Both sexes excavate, although limited data (1, 71) indicate that the male predominates in this activity.

Birds excavate in bouts of up to 20–30 min, and often relieve one another (66). A bird pecks in brief series punctuated by pauses during which it flings wood away and/or is vigilant. Within a series, may peck at rates of 3–6/s (1). Pecking rate up to 50/min, and excavating birds may be heard up to 180 m away (66). Birds excavate soft sapwood between bark and heartwood, and may plug crevices with shreds of bark (25, 71, 77). Both sexes bring lining materials to the cavity, an activity that may continue well into the incubation period (1). When reusing the nest site for a second brood, the birds may add a small amount of material to the cavity (Norwood and Norwood 79, 86). Time required for nest completion varies considerably, usually 1–6 wk (66, 1).

Structure And Composition Matter

Of 16 nests in Georgia, pine seed wings were reported in 88%, cotton in 38%, feathers in 31%, wool in 31%, cocoon fibers in 25%, and cypress bark strips in 25% (1). Also noted were unidentified bark shreds, pine needle fascicles, pieces of corn shuck (Zea mays), pine needles, inner bark of pine, inner bark of red cedar (Juniperus virginiana), strands of Spanish moss (Usnea sp.), soft weed stalks, grass rootlets, and decayed wood chips. Other observers have noted similar materials. Pine seed wings may constitute 50–100% of the bulk of the nest (66, 1).

Dimensions

The cavity entrance is either round or vertically oblong. Mean entrance height 5.0 cm and width 3.8 cm, diameter inside cavity 4.3–10.2 cm, and mean cavity depth 17.8 cm (n = 14; 1). Cavity entrances “often jagged, sometimes circular, with most diameters ranging from 2.5–3.8 cm” (n = 34 from throughout species range; 77). In Louisiana, mean cavity entrance size 3.3 x 3.3 cm (n = 16), and cavity depth 12.3 cm (range 7.6–20.7, n = 18; 71). Cavity depths from sample throughout range were 7.6–40.6 cm, most 12.7–25.4 cm (n = 69; 77).

Microclimate

Cavity orientation is highly variable: of 35 nests in Louisiana and Arkansas, 31% north, 26% west, 23% south, 20% east (n = 22 [71]; n = 13 [JHW]). Likewise, no bias in orientation found in s. Florida nests (G. Slater pers. comm.). Cracks in nest exterior are “caulked”—i.e., stuffed with bark or other material (1, 71, 77). Nests are known to fail from water seepage during cold spells (71) and excessive heat (79). High summer temperatures in the se. U.S. may have helped select for early nesting phenology and the paucity of second broods.

Maintenance Or Reuse Of Nests, Alternate Nests

Little information, but since nests are usually placed in well-decayed snags, many nest sites may fail to survive for reuse. In s. Florida, 1 group used the same cavity for 2 yr, and 1 group used a cavity for 3 yr—both in cypress snags, which decay very slowly (49). Other anecdotal accounts exist—e.g., a cavity used for 3 yr (29) and nest boxes used for second broods (Norwood and Norwood 79, 86; 71).

Nonbreeding Nests

Often cavities are excavated—entirely or partly—and abandoned without being used for nesting.

Eggs

Shape

Short subelliptical to short oval.

Size

Mean 12.3 mm (range 11.4–14.2) x 15.5 mm (range 14.1–16.7) for all but s. Florida birds (n = 50; 1). For s. Florida birds, mean 11.8 mm (range 11.0–12.8) x 15.0 mm (range 14.1–16.1, n = 28; 1).

Mass

For 4 fresh eggs from Georgia, mean 1.10 g (range 1.05–1.15). For 15 eggs from S. Carolina, calculated mean 1.16 g (range 1.05–1.36; 1). Each egg 10–11% of mass of breeding female.

Color

Ground color white, light creamy, or buffy, with markings of reddish brown, vinaceous cinnamon, purplish, or lavender, evenly distributed as fine dots or concentrated at larger end as blotches. Eggs are more profusely marked than those of other nuthatches (66).

Surface Texture

Smooth, with little gloss (66).

Eggshell Thickness

No information.

Clutch Size

Mean 5.10 ± 0.91 SD (range 3–7 [1 record of 9], n = 369 from throughout species range; 77). Clutch size is significantly lower in Florida than in the remainder of the range (mean 4.50 ± 0.80 SD), and declines significantly with initiation date (77). In Georgia, mean 5.2 (range 4–7, n = 67; 1). In Louisiana, mean 4.29 (range 3–6, n = 58; 71). In Texas, mean 4.9 + 0.2 SE (n = 24, Dornak et al. 2004). From CNRP data, mean 5.41 ± 1.21 SD (range 4–7, n = 28). Lowest mean clutch size among 4 North American nuthatches (87).

Egg-Laying

Eggs laid in early morning at rate of 1/d (78, 1, but information limited).

Incubation

Onset Of Broodiness And Incubation In Relation To Laying

Incubation is initiated after the clutch is complete, or nearly complete (78, 1).

Incubation Patch

Single vascularized brood patch, developed only by the female, may occur early Mar–early May. Maximum width 15–22 mm across breast; narrower across abdomen (1).

Incubation Period

Mean 14 d (66, 1).

Parental Behavior

Female alone incubates, but the male may regulate the incubation rhythm by calling the female off the nest. The male feeds the incubating female at the nest, mean of 1.4 times/h (n = 8 h; 1) in Georgia, 2 times/h (n = 9 h; 71). In Texas, female fed 1.4 times/h + 2.0 SD when group size = 2 (n = 7 nests); when group size >2, breeding male feeds the female 1.7 times/h ± 1.9 SD, and the helper feeds the female 0.6 times/h (n = 8 nests; Thompson 2000). In 8 h of observation at 1 Georgia nest, eggs were covered 80% of time; mean period on the nest 42 min (range 15–100); mean period off the nest 11 min (range 5–23). Eggs are shifted regularly during incubation (1).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

No direct information, but Morris (71) reported eggs being covered with nesting material until clutch is complete.

Hatching

Preliminary Events And Vocalizations

No information.

Shell-Breaking And Emergence

Few data. Most clutches hatch within 24 h, but some may take up to 2 d (1, 71).

Parental Assistance And Disposal Of Eggshells

Eggshell removal not directly observed, but Norris (1) presented evidence that it occurs.

Young Birds

Condition At Hatching

In Georgia, n not specified (1): Mass 1.2 g, bill length (from nostril) 1.5 mm, forearm 5.0 mm, tarsus 5.3 mm. Natal down well-developed in coronal, occipital, middorsal, and scapular regions, with light mouse gray color. Skin tannish pink, darker dorsally, redder in pelvic region, translucent over belly such that organs are partly visible. Bill light or horn yellow, becoming abruptly whitish on 8-mm-wide gape. Mouth interior and tongue bright yellow; feet light pinkish; eyes closed. At 1 d, young can give pseep calls (up to 16 in 20 s), raise head and gape, flick and flutter forelimbs, jerk legs, and open and close toes. Breathing rate (at 85–95°F) at 1 h, 36 cycles/min; at 1 d, 45 cycles/min.

Growth And Development

See Table 2 for measurement data.  Sheaths for all feather tracts appear at 6–9 d. Eyes begin to open at about 7 d; preening and perching abilities develop at 13–15 d; flying ability develops at about 18 d. Breathing rates increase from 72 breaths/min (at 5 d) to 100–112/min (at 6–7 d) to 90–144/min (at 9 d) to 240/min (at 15 d). Young beg for food and often receive food at the cavity entrance in the final days of the nestling period (1).

Parental Care

Brooding

Female alone broods roughly half the time during the first few days of the nestling period (mean session length 13.8 min), then sparingly after that (1). Parents may brood young at night (78), but may not brood at night during the latter half of the nestling period (84, 82).

Feeding

Young nestlings are brought diverse small or soft-bodied arthropods; no food is regurgitated. Older nestlings are given larger items, such as whole cockroaches, and occasionally pine seeds with hard covering removed (1). In Louisiana, broods were fed at a mean rate of 12.5 times/h at 1–5 d, 15.7 times/h at 6–10 d, and 17.1 times/h at about 11 d (30 h; 71). In Georgia, 5 nestlings at 1–3 d were fed 8.8 times/h by a pair, while 5 nestlings at 6–9 d were fed 20.0 times/h by 4 birds (1). In Texas, mean feeding rate was 5.8 + 2.3 SD times/h for pairs (n = 7 nests), 5.2 + 2.4 SD times/h for cooperative groups (n = 8 nests, Thompson 2000). Male does most of the feeding early in the nestling period, when the brooding female may eat some delivered food; however, the female does at least half of the feeding later in the nestling period (1, 71). Average distance of adult foraging flights is 80.6 m (range 6.1–163.6, n = 36, in longleaf pine with 30% canopy cover; 1). Presumably such distances are greater for nuthatches nesting in open areas outside pine stands.

Nest Sanitation

Beginning 3 d after hatch, both sexes carry fecal sacs away; removal rate increases with nestling age (1). Fecal sacs removed at an average rate of 1.2 + 1.1 SD times/h for pairs (n = 7 nests) and 1.8 + 1.1 SD times/h for cooperative groups (n = 8 nests, Thompson 2000). Little information on nest parasites, but no obvious ectoparasites were found on chicks within 3–4 d of hatching after they died in the nest from overheating (79).

Carrying Of Young

In Arkansas, a pair was observed carrying a dead young covered with ants out of the nest cavity after nest failure. The cavity was not reused that year for nesting; not known whether it was used for roosting (JHW).

Cooperative Breeding

Helpers

Throughout the range of this species, helpers are found at ~ 20% of territories, but extent varies widely. In n. and s. Florida, 22.7% + 11.4 (SD, n = 152) and 17.3% + 16.1 (n = 195) of territories, respectively, had helpers (range 10 – 32%, Cox and Slater 2007). Results differ from an earlier study in s. Florida where 60% (35 of 58) of territories had helpers (49). In Georgia, 3 of 17 (18%) breeding pairs contained 1 helper (1). In ne. Florida, Miller and Jones (1999) found 3 of 13 (23%) territories had 1 helper. In Texas, 6 of 13 (46%) territories in urban environment had helpers (Thompson 2000), while in a forest setting Dornak et al. (2004) found 2 of 24 (8%) territories had 1 helper.

Helpers assist with territorial defense, nest construction (excavating and nest-building), nest sanitation, and feeding of nestlings, fledglings, and the female at the nest (1, Slater 1997, Thompson 2000, Cox and Slater 2007). Helpers are not known to roost with pairs in the breeding season. Helpers appear to be closely related to breeders (Cox and Slater 2007). In Florida, the breeding male of three adjacent territories included a father and 2 sons; in six other cases, adjacent territories were held by sibling or a parent-offspring combination.

Mean group size in s. Florida was 2.7 birds (n = 58, 32 with 3 birds and 3 with 4; 49). In urban population in Texas, mean size of cooperative groups was 4.0 (n = 6, 4 with 3 birds, 1 with 4 adults, and 1 with 6; Thompson 2000). Cox and Slater (2007) found most helpers were second-year males (ca. 1 yr old, thus in their 2nd summer), assisting at nest of at least 1 parent (n = 8); in 2 cases, males assisted parent for > 3 yr. Only one reported case of female helper, who also assisted with incubation (Cox and Slater 2007). Houck and Oliver (73) report a brood raised by 2 pairs, but present no convincing evidence that the group was not 1 pair and 2 helpers. When a primary male was killed during incubation period, a helper that had been contributing heavily before this continued providing for female (1). Adults from neighboring territories provided assistance at neighboring nests following failure of their nest (Cox and Slater 2007, 1).

Hypotheses for cooperative breeding have varied. Species apparently has a strongly male-biased sex ratio, which might constrain breeding opportunities for males. Lower annual survival by females in n. Florida is thought to promote cooperative breeding (Cox and Slater 2007). In contrast, no gender-based survival differences were found in s. Florida, suggesting food resources or territory quality may constrain breeding opportunities and promote cooperative breeding (Cox and Slater 2007).

Results Of Helping

The presence of helpers did not increase productivity in n. Florida (pair: 4.16 young/successful nest, n = 117; with helpers: 4.35 young/successful nest, n = 34) or s. Florida (pairs: 2.90 young/successful nest, n = 139; with helpers: 2.94 young/successful nest, n = 17; Cox and Slater 2007). However, an earlier study in s. Florida found groups with ≥3 individuals were significantly more successful at fledging young (70% nesting success; n = 35 nests) than pairs (48% success; n = 23 nests, 49). Hypotheses to account for this difference remain untested. In Texas, productivity was slightly higher, although not significantly, for pairs with helpers (n = 4.4 young/successful nest) than for pairs on their own (n = 3.8 young/ successful nest; Thompson 2000). In ne. Florida, three nests in territories with helpers were all successful, whereas 8 of 12 (67%) nests by pairs were successful (Miller and Jones 1999).

Visitation rates during the nesting season (nest-building, incubation, nestling) did not differ between pairs (8.59 trips/hr, n = 8 nests) and cooperative groups (9.10 trips/hr; n = 7 nests, Thompson 2000). However, the rate of guarding visits for cooperative groups (0.98 trips/hr) was significantly higher than for pairs (0.51 trips/hr), particularly during the nestling stage. In the presence of helpers, breeding females significantly decreased their nest visitation rates, particularly during the nestling stage (Thompson 2000).

Brood Parasitism by Other Species

Two accounts exist of unsuccessful nest parasitism attempts by Brown-headed Cowbirds (Molothrus ater; Louisiana: 71, N. Carolina: CNRP).

Fledgling Stage

Departure From Nest

May depart nest in morning or afternoon; time between first and last bird to depart 2.5–6 h. Young are not forced out by parents, and are capable of flying well on initial departure, but may lose altitude or become temporarily grounded (1, 71). Nestlings fledge at 18–19 d of age, and young do not return to the nest after fledging.

Growth

See Young birds, above.

Association With Parents Or Other Young

Dependent on parents for food 2–4 wk after fledging (see below). Family groups remain together throughout the summer, and may merge with other family groups (1).

Ability To Get Around, Feed, And Care For Self

From 1:  Young depend on parents for food after fledging. Food delivery rate varies; up to 1 delivery/5 min. Young move very little in first few days, but later follow parents widely. Siblings may perch together side by side and preen one another. First foraging attempts noted at 20–21 d after hatching (2–3 d after nest departure), but “repeated and effectual” foraging not noted until 32 d (14 d after departure). At 36 d of age, fly-catching attempts noted. Fledglings > 27 d old still beg food from adults, but at 42 d begging is uncommon and ineffective, and at 44–45 d no begging observed, although young birds remain in general vicinity of adult.

Norwood and Norwood (79) noted young being fed by adults 12 d after fledging but foraging independently at 25 d.

Immature Stage

Males may act as helpers, assisting parents in raising young, before attempting breeding (see Cooperative breeding, above). No other information specific to immature birds.

Recommended Citation

Slater, G. L., J. D. Lloyd, J. H. Withgott, and K. G. Smith (2021). Brown-headed Nuthatch (Sitta pusilla), version 1.1. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.bnhnut.01.1