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

Demography and Populations

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Measures of Breeding Activity

Age At First Breeding; Intervals Between Breeding

From Cox and Slater 2007, except as noted. First-year male birds may breed or may remain as helpers at nests of parents. Less commonly, males may remain on natal territory for up to 3 years (2 of 11 instances of cooperative breeding). Most adults breed yearly (1). Mean percentage of territories with nests 85.2% ± 9.2 SD and 83.2% ± 22.4 SD in n. and s. Florida, respectively. In some years in Florida, however, many pairs apparently do not attempt nesting (across several years in n. and s. Florida, percentage of color-banded pairs or groups attempting to breed ranged from 33% to 100%).

Clutch

See Breeding: eggs, above. May produce second clutch if first is destroyed. Rarely lays second clutch after raising successful brood (see below).

Annual And Lifetime Reproductive Success

In s. Florida, nest success rates ranged from 48 to 85% across 2 sites and years; groups containing helpers showed significantly higher success (see Breeding: cooperative breeding, above). Average nest success rate 65% (n = 141) in 2 populations studied in s. Florida from 1998-2003 (Lloyd and Slater 2007). Eleven of 15 (73%) of nests observed in n. Florida fledged at least 1 young (Miller and Jones 1999). Fourteen of 24 (58%) nests fledged young in e. Texas (Dornak et al. 2004).

In 2 s. Florida populations, productivity ranged from 1.36 ± 0.45 SE young/breeding attempt to 2.10 ± 0.32 SE (n = 60 nests; 49). Average productivity from 1998-2003 in a population reintroduced to Long Pine Key, Everglades National Park, Florida (2.0 young fledged/nest) was similar to source population in Big Cypress National Preserve, Florida (1.9 young fledged/ nest) (Lloyd and Slater 2007). At fifteen nests studied in n. Florida, 2.7 ± 1.9 SD young fledged/ nest (Miller and Jones 1999). Groups of 3 had higher nest success (3 of 3 nests fledged ≥ 1 young) than pairs (8 of 12 nests fledged ≥ 1 young) and so tended to fledge more young (3.3 ± 2.1 SD) than pairs (2.4 ± 1.9 SD) (Miller and Jones 1999). At 24 nests in e. Texas, average productivity 2.7 young fledged/nest (Dornak et al. 2004).

Of successful nests in s. Florida, most produced 4 (22%), 3 (15%), or 2 (20%) fledglings; nests fledging 1 (5%) or 5 (3%) young were rare (Lloyd and Slater 2007). Successful nests in n. Florida fledged more young (without helpers: 4.16 young/successful nest; with helpers: 4.35 young/successful nest) than nests in s. Florida (without helpers: 2.90 young/successful nest; with helpers: 2.94 young/successful nest), but presence of helpers had no effect on number of young fledged from successful nests in either location (Cox and Slater 2007). In e. Texas, successful nests produced 3-6 young (Dornak et al. 2004). In Louisiana, a mean of 3.0 young fledged from nests that progressed beyond egg-laying stage (n = 13 nests) and 4.09 young fledged/nest that successfully fledged at least 1 young (n = 33 nests), with 62.8% of nestlings successfully departing nest (71). In Arkansas, nest success following egg-laying was 56% (n = 7; 81). Lifetime reproductive success not known.

Factors potentially limiting reproductive success may include nest predation (see Causes of mortality, below), competition for cavities (see Behavior: social and interspecific behavior, above), and density of snags for nesting (see Habitat: breeding range, above).

Number Of Broods Normally Reared Per Season

Normally 1, rarely 2. As with many passerine species, second broods may be less rare than had been thought; the many late nesting dates recorded from southern states suggest this (22). However, the few quantitative studies done reinforce the impression that second broods are infrequent. In s. Florida, 2 of 59 (3.4%) nesting pairs and 2 of 36 (5.6%) nesting pairs whose first nests were successful attempted second broods (49). Of 141 territories monitored in s. Florida from 1998-2003, only 3 pairs made second attempts following a successful first nest (Lloyd and Slater 2007). In n. Florida, 0 of 9 territories monitored attempted second nest after successful first nest (Miller and Jones 1999). In Louisiana, 1 of 22 (4.5%) pairs and 1 of 13 (7.7%) pairs whose first nests were successful reared a second brood (71). In Georgia, none of 17 pairs observed attempted second broods (1). In Texas, two pairs that nested in streetlights on a college campus successfully raised two broods; in the same study, 0 of 24 birds nesting in pine forest raised second broods (Dornak et al. 2004).

Anecdotally, 2 cases of second broods described from N. Carolina (Norwood and Norwood 79, 86), and McNair (77) provides citations for other possible second broods. Because of this species' propensity to excavate new holes, Martin (87) predicted that double-brooding should be rare in Brown-headed Nuthatch compared to other North American nuthatches. The long dependency period of juveniles may also limit second brood attempts (Slater 1997)

Renesting after failure of the initial nest is far more common. Reported to renest up to 4 times/season when broods are destroyed (Smithwick 1899 in 1), although this seems extreme on the basis of later studies. Slater (49) found that 3 of 22 groups (14%) successfully completed a second clutch after initial failure. In 2 s. Florida populations, renesting occurred on 10 of 49 territories (20.4%) that lost a first nest (Lloyd and Slater 2007). In n. Florida, 2 of 15 (13.3%) nests observed may have been renesting attempts following failure (Miller and Jones 1999).

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

Not known.

Life Span and Survivorship

Maximum recorded life span of 9 yr by a male in n. Florida (J. Cox, pers. comm.). Maximum longevity from USGS Bird Banding Lab is 5 yr 9 mo (USGS 2012). The following calculations were made by Norris (1), on the basis of observed ratios of adults to subadults: theoretical annual survival rate, 0.54; life expectancy, 2.2 yr from first breeding season; theoretical maximum life expectancy, 8 yr. See 1 for methods and assumptions implicit in these calculations.

Survival rate calculated by Norris (1958) is generally lower than empirical estimates. Based on mark-recapture analysis, apparent annual survival of males in n. Florida (77.8% ± 4.7 SD) higher than female survival (66.1% ± 5.3 SD); in 2 s. Florida populations, males (69.3% ± 15.8 SD) and females (68.7% ± 13.1 SD) had similar annual survival (Cox and Slater 2007). Average annual survival 2001-2007 in a population reintroduced to Long Pine Key, FL, was 63% (95% CI = 55% - 71%). As with the s. Florida populations studied by Cox and Slater (2007), substantial annual variation in apparent survival for this population was evident too: from 43% (95% CI = 30% - 58%) in 2006 to 82% (95% CI = 60% - 94%) in 2003 (Lloyd et al. 2009).

Disease and Body Parasites

Diseases

No information.

Body Parasites

Filarial nematodes found in 1 of 8 specimens from sw. Georgia (88); nematodes found in 3 of 9 birds in n. Georgia, as well as unidentified cestodes (1). Two of 7 birds infected with hematozoans—1 with Haemoproteus and 1 with Leucocytozoon (89)—and 1 of 5 Georgia birds infected with Leucocytozoon sp. (Love et. al. 90). Two of 15 Louisiana birds infected with the eye worm Oxyspirura pusillae, having 16 eyeworms between them (91); in Georgia, 3 birds had O. pusillae and 2 had O. petrowi (1). Also in Georgia, light infestations of Mallophaga lice (Brueelia and Myrsidea), and 1 blowfly pupa (Protocalliphora sp.) record (1). One of 2 individuals in Texas contained dilepidid tapeworm Orthoskrjabinia rostellata (McAllister and Bursey 2003).

Causes of Mortality

Collision

Two individuals died following collision with a glass door in Texas (McAllister and Bursey 2003). Collision with anthropogenic structures unlikely a frequent or significant source of mortality given the mostly sedentary lifestyle of this species.

Exposure

No information.

Predation

Few data; see Behavior: predation, above. One record of adult predation by Swallow-tailed Kite (Cox In Press b). Most mortality probably occurs in nesting. Nest failure rates in Louisiana from Morris (71) were 41.8% for museum records (n = 63) and 71.4 and 25% for nests monitored in the field (n = 22 over 2 yr); major causes of failure were predation and windstorms. In s. Florida, nest failure rates of 15–52% are attributed primarily to predation by mammals and snakes; 1 nest usurped by Red-bellied Woodpecker (49). In study in n. Florida, only 24% of nest failures due to predation (Cox and Slater 2007). At 2 nests in this study, eggs depredated by broad-headed skink (Eumeces laticeps). In e. Texas, 10 of 24 nests (41.7%) failed and predation was believed the primary cause (Dornak et al. 2004). Dornak et al. (2004) reported the rat snake Elaphe obsoleta as a predator of eggs and nestlings. In Arkansas, nest failure of 44% (n = 7) estimated to be due to snakes, primarily during nestling stage (81).

Five females in n. Florida population killed by red ratsnakes (Elaphe guttata) or small mammals while incubating eggs or brooding young (Cox and Slater 2007).

Fire

Cox and Slater (2007) reported that 21% of nest failures in n. Florida caused when nest cavity destroyed by prescribed fire.

Competition With Other Species

Competition apparently exists for food with Pine Warblers in winter (59) and for nest sites with various cavity-nesting species (see Behavior: social and interspecific behavior, above). These pressures may regulate foraging and nesting success, but there is no evidence of mortality directly caused by competition.

Population Spatial Metrics

Initial Dispersal From Natal Site

Fledglings usually leave the immediate vicinity of the nest within days or hours after fledging, but may remain in the area for weeks to months afterward, or longer if they act as helpers (1). Higher genetic relatedness among males on territories within 1.3 km of one another indicates limited male dispersal from the natal site (Haas et al. 2010). Field observations of color-banded individuals support these genetic findings. Seven of 11 (63.6%) second-year males relocated in a n. Florida population established territories or acted as helpers on territories <300 m from their natal site, most often adjacent to the natal territory (Cox and Slater 2007). Four of 11 (36.4%) second-year males relocated dispersed an average of 1.4 km from their natal site (Cox and Slater 2007). No second-year female was relocated on the study site, suggesting female-biased dispersal (Cox and Slater 2007). However, estimates based on resighting marked individuals oversample individuals moving short distances (i.e., males that defer breeding to act as helpers) and probably produced biased estimate of the overall distribution of dispersal distances. Interestingly, average distance between territories of genetically related pairs of males (1.6 km) and females (1.8 km) were similar in a n. Florida population, suggesting broadly similar dispersal strategies between the sexes, excluding the perhaps small proportion of males that defer breeding to act as helpers (Haas et al. 2010).

Fidelity To Breeding Site And Winter Home Range

Apparently sedentary year-round, and shows site fidelity among years (62, 1, 60). Of 49 territorial, color-marked birds in Long Pine Key, Everglades National Park that were present for > 2 years, 36 (73.4%) occupied the same territory every year, for up to 6 consecutive years (G. L. Slater, unpublished data). The remaining 13 (26.6%) switched territories between years, but no individual switched territories more than once during the period of observation (1998-2006; GLS, JDL). Studies of marked birds outside of breeding season lacking and thus details of winter home range remain unclear. Incidental observations of banded individuals on or near breeding territories during the winter suggest year-round residency, at least in s. Florida (GLS, JDL).

Dispersal From Breeding Site Or Colony

Measurable genetic differentiation between nearby breeding populations (separated by <40 km; Haas et al. 2010), tendency of SY males to remain on or near natal territories (Cox and Slater 2007), and failure to recolonize vacant but suitable habitat (e.g., Long Pine Key, Everglades National Park; Lloyd et al. 2009) suggest that movement among populations limited.

Home Range

In winter, often participates in mixed-species flocks; Morse (60) estimated range of winter flocks in Louisiana pine forest to be 16.7 ha. See Behavior: spacing, above, for information on breeding-season territories.

Population Status

Numbers

Breeding Season. See Table 3 for density estimates from various studies. Breeding Bird Censuses in pine habitat from Virginia to Florida give mean of 4.5 pairs/40 ha ± 1.5 SE (range 1–12, n = 18; 34). Recorded on 215 of 888 Breeding Bird Survey (BBS) routes in se. U.S. (1966–1985; 34). Mean relative abundance on BBS routes in 7 states (1966–1995) was 1.66 birds/route, ranging from 0.90 in Mississippi to 3.42 in S. Carolina (92). More recently (1980-2006; Figure 6), average relative abundance on BBS routes greatest (>3 – 10 birds/route) in southern Piedmont BCR of Alabama and Georgia; isolated pockets of high relative abundance also found on BBS routes the Southeastern Coastal Plain of Florida and N. Carolina (Sauer et al. 2011; Figure 7).

Nonbreeding Season. See Table 3 for density estimates from various studies. Winter Bird Population Survey data in pine habitat from Virginia to Florida show mean of 2.7 pairs/40 ha ± 0.7 SE (range 1–5.5, n = 9; 34). On Christmas Bird Counts (CBCs), highest number of individuals occurred in s. Dorchester Co., MD, in late 1960s and early 1970s; in s. Arkansas in late 1970s; in Atlanta, GA, in early 1980s; and on Sapelo I., GA, in 1990s. After 2000, high counts at either McClellanville, SC (2001, 2004, 2005) or St. Catherines Is, GA (2003, 2006-2010). Highest count during CBC was 635 at St Catherines Is, GA, 2006 (Ortego 2007). Previous high count was 482 individuals in s. Dorchester Co., MD, in 1959 (93).

Trends

Declined significantly (-0.6%/yr; 95% CI = -1.1%/yr – -0.1%/yr) rangewide based on BBS routes surveyed between 1966 and 2010 (Sauer et al. 2011). This amounts to an estimated decrease in population size of approximately 23% over the period. Decline was most pronounced from 1966-1990 (-0.9%/yr; 95% CI = -1.7%/yr – -0.2%/yr; Sauer et al. 2011). Indeed, no trend evident from BBS routes in 1990 – 2010 (-0.1%/yr; 95% CI = -0.8%/yr – 0.5%/yr) (Sauer et al. 2011).

Significant declines noted from 1966 – 2010 in 3 Bird Conservation Regions (BCR): Peninsular Florida (-3.9%/yr, 95% CI = -7.1%/yr – -2.5%/yr), Southeast Coastal Plain (-1.1%/yr, 95% CI = -1.8%/yr – -0.5%/yr), and West Gulf Coastal Plain (-1.4%/yr, 95% CI = -2.6%/yr – -0.1%/yr) (Table 3). Declines in Southeast Coastal Plain BCR most pronounced prior to 1990; other 2 regions showed steadier decline across all years of BBS. No significant increases in any BCR. One state – Tennessee – showed significant increase from 1966 – 2010 (18.2%/yr, 95% CI = 6.0%/yr – 38.4%/yr) and 2000 – 2010 (22.3%/yr, 95% CI = 4.5%/yr – 78.4%/yr), but individuals detected on only 4 routes and increase reflects recent range expansion (Renfrow 2003). Significant declines in Louisiana from 1966 – 2010 (-2.7%/yr; 95% CI = -4.5%/yr – -1.0%/yr). Decline in Louisiana was consistent across all years; no evidence of slowing post-1990. No other states showed significant trends.

In a study of the population reintroduced to Long Pine Key, Everglades National Park, population growth rate was positive from 2001 – 2005, but became negative thereafter (Lloyd et al. 2009). Declining population growth rate was associated with a concomitant decline in apparent survival of adults (Lloyd et al. 2009). Censuses on Grand Bahama I. yield unclear picture of trends, apparently due to sensitivity of results to method of survey, but most studies concluded that the island population might be in imminent danger of extirpation (Hayes et al. 2004, Lloyd and Slater 2011).

Point-count surveys on National Forests in the southern US indicated an increase from 1992 – 2004 (3.7%/yr; 90% CI = 0.4%/yr – 7.0%/yr; La Sorte et al. 2007). Statistically significant, positive trends were found for the Southern Cumberland/Ridge and Valley physiographic region and the East Gulf Coastal Plain physiographic region. No physiographic region showed evidence of statistically significant declines during the period of observation.

Population Regulation

No studies have directly and rigorously addressed the question of population regulation in this species, but enough information exists in the literature to make some reasonable speculations. First, density measurements in various habitats (see Population status, above) suggest that availability of suitable habitat may limit populations. Indeed, at Long Pine Key, Everglades National Park, average group size increased as population size increased, suggesting local habitat was rapidly filled (Lloyd et al. 2009). Suitable habitat is best characterized as mature pine forest, and limiting features appear to include openness of the understory and density of snags. Human influences on these features may include logging and changes in fire regime. Local population declines have been correlated with logging of mature pine forest (94, 95). Across three different habitats spanning a riparian-to-upland gradient, abundance was greater in stands burned during the growing season than in stands that were not burned (Allen et al. 2006), a relationship attributed to effects of fire on vegetation structure. Abundance was greater in thinned pine plantations, which Wilson and Watts (1999) attributed to higher density and height of understory vegetation in unthinned plantations; likewise, Dornak et al. (2004) found that snags used for nesting were surrounded by less dense midstory than snags not used for nesting. However, Lloyd and Slater (2011, 2012) found no effect of fire history on density in south Florida. Changes in fire regime may also limit population size via effects on density of snags (see below).

Within mature pine forest, reproductive output may be limited by the availability of snags suitable for nesting. High snag density may decrease probability of nest predation or frequency of encounters with cavity competitors (49). In s. Florida, nests were placed in areas of especially high snag density (49) and breeding productivity (young fledged/nest) increased as density of large (≥15 cm diameter at breast height) pine snags surrounding a nest site increased (Lloyd and Slater 2007). In Texas, nesting success was positively associated with the number of snags surrounding the nest site (Sullivan 2011). Occasional use of woodpecker holes, telephone poles, fence posts, and nest boxes suggests nest-site limitation due to unavailability of natural snags.

Fragmentation of habitat may also be detrimental, since apparently weak flying ability and generally sedentary character make it unlikely that individuals will disperse to recolonize distant fragments following local extirpations.

Agonistic encounters with cavity competitors could depress nesting success. There is no evidence in natural settings, however, that cavity competitors are regularly able to exclude nuthatches from nest sites once established.

Variety of arthropod prey taken is broad, so food limitation in warmer months seems unlikely. However, variability of pine seed crops could be an important factor regulating populations via overwinter survival, particularly in forests with only one species of pines or lacking consistent seed-producers (loblolly, short-leaf). Unlike the nomadic Red-breasted Nuthatch, which ranges widely in winter, the Brown-headed Nuthatch apparently remains sedentary despite reliance on a pine seed diet in winter. Populations from year to year seem generally stable despite cone crop fluctuations, but more study is needed.

Competition for food with Pine Warblers forces partitioning of foraging space (59), but more study is needed to determine whether such competition has any population-level effect.

Predation on nests may have large impact on population growth. Low height of many nests, as well as deteriorated condition of many nest snags, may make them especially vulnerable to terrestrial climbing nest predators, such as raccoons (Procyon lotor), house cats, and rat snakes (Elaphe spp.; Withgott 81, 82, 49). Early breeding, however, may help reduce snake predation, since rat snakes climb trees less frequently in spring than in summer (81, unpubl. data).

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