Eastern Kingbird

Tyrannus tyrannus


Demography and Populations

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Figure 7. Relative abundance of Eastern Kingbird during the breeding season.

Based on data from the North American Breeding Bird Survey, 2011–2015. See Sauer et al. (2017) for details.

Figure 8. Regional trends in Eastern Kingbird breeding populations.

Based on data from the North American Breeding Bird Survey, 1966–2015 (Sauer et al. 2017). Data show estimates of annual population change over the range of the survey; areas of increase are shown in blue and declines are shown in red. See Sauer et al. (2017) for details.

Measures of Breeding Activity

Age at First Breeding

Capable of breeding at ca. 1 yr of age, but in at least one population ≥ 50% of individuals may not breed in their first potential breeding season (142). Negative density dependent influence of population size on proportion to breed in first potential breeding season is strong (142); it is unknown whether this is true of other Eastern Kingbird populations. Records of banded birds indicate that once breeding begins, it occurs annually (MTM).


Of 1,357 egg sets from across North America: 2 eggs (6.0%), 3 eggs (41.9%), 4 eggs (46.6%), and 5 eggs (5.5%) (MTM, unpublished data). Field studies generally indicate slightly smaller clutch sizes than recorded by egg sets, with average values of 3.1 ± 0.63 SD (n = 42) in western New York (9), 3.2 ± 0.58 SD (n = 903) in central New York (MTM, unpublished data), 3.7 ± 0.56 SD (n = 54) in southeastern Ontario (6), 3.3 ± 0.66 SD (n = 230) in eastern Kansas (MTM, unpublished data), 3.4 ± 0.50 SD (n = 30) from Montana (5), and 3.5 ± 0.61 SD (n = 573) in eastern Oregon (MTM, unpublished data). All aforementioned studies (except Ontario) include both initial and replacement nests. Field studies and analysis of museum egg sets indicates that clutch size increases from east to west across North America. Museum egg sets also indicate clutch size does not increase with latitude (MTM, unpublished data). The East–West difference in clutch size exists mainly because of fairly abrupt increase beginning at 100th Meridian, the traditional boundary between more mesic eastern North America and the xeric west (MTM, unpublished data). Increase in average clutch size from east to west across North America mirrors interspecific differences in genus Tyrannus (MTM, unpublished data).

Offspring size at fledging correlated inversely with brood size in New York (23, 13), but not Kansas or Oregon (MTM, unpublished data). Starvation in large broods common only when prolonged periods of cold, wet weather reduce insect availability and adult foraging success (8, 9, 13). More frequent rain in eastern North America may reduce temporal reliability of food supplies and increase probability that young in large broods starve (MTM), possibly giving a general explanation for why Eastern Kingbirds lay smaller clutches in eastern North America. On the other hand, nest predators are main cause of most nestling deaths. Parents devote substantial time to predator vigilance, at cost of feeding young (see Breeding: parental care, above), which may compromise their ability to feed larger broods.

Intrapopulation variability in clutch size associated with year, individual female, and date of laying, but not habitat. Clutch sizes in upland and lakeshore habitats do not differ (6), nor do they differ among riparian, floodplain, and upland habitat (14). In first clutches, clutch size declines with later dates of laying in every population studied (9, 11, 6, 7), and in years when breeding is early, clutch size tends to be large (11; MTM, unpublished data). Rate of decline in clutch size is 0.020–0.045 eggs/d (9, 11, 6). Clutch size in replacement nests often smaller than in first nests (6), but not always; females producing small first clutches (2 or 3 eggs) tend to produce the same-sized or larger replacement clutches (MTM, unpublished data). Clutch size does not vary with age, but differences among females (corrected for decline with laying date) are repeatable (r = 0.282, P < 0.001, n = 60 females) (160).

Annual and Lifetime Reproductive Success

Nest success (% nests to fledge ≥ 1 young) varied from 21 to 37% (mean = 29.1%, n = 3 yr) (11) in eastern Kansas, 29.5 to 67.2% in central New York (mean = 48.6%, n = 12 yr) (MTM, unpublished data) and 19.7 to 56.5% in eastern Oregon (mean = 36.1%, n = 10 yr) (MTM, unpublished data), with an overall mean of 41.3% ± 13.9 SD (n = 25 yr). Nest success in Ontario is comparable (lakeshore = 38%, upland = 52%) (6). Percentage of nests to survive from egg-laying to hatching, and then from hatching to fledging in eastern Kansas (0.502 ± 0.102 SD vs. 0.565 ± 0.118 SD, n = 3 yr), central New York (0.681 ± 0.124 SD vs. 0.736 ± 0.108 SD, n = 13 yr) and eastern Oregon (0.521 ± 0.103 SD vs. 0.686 ± 0.144 SD] n = 10 yr) indicates greater success during the nestling period in Kansas (tpaired comparisons = 4.69, P = 0.043) and Oregon (t = 3.48, P = 0.007), but not New York (t = 1.62, P = 0.132) (MTM, unpublished data). Lower success in Kansas due to loss of more nests to high winds associated with thunderstorms, and higher rates of nest depredation (8), while lower success in Oregon due almost exclusively to high nest predation (MTM, unpublished data).

Successful females raise 1 brood/yr. In central New York, nearly 70% of failed first nesting attempts were replaced (mean 68.4%, n = 57 nests; MTM). In eastern Oregon, about 60% of failed first nests were replaced (58.3%, n = 108 nests) (16). Renesting was less common in British Columbia (7 of 36 females) (157). In central New York, all initial nests that were destroyed while being built were replaced, compared to 82.5% (n = 40) of nests lost during incubation, and 35.2% (n = 17) that failed during the nestling period (MTM). Probability of renesting declined with failure date in eastern Oregon (16). Taking renesting into account, annual breeding success (percent females to fledge at least 1 nestling) over 6-yr period in New York averaged 58.5% ± 15.0 SD, range 32.9–77.0 (MTM). Average number of fledged young/female over same period was 1.5 nestlings/yr ± 0.40 SD (range 0.8–1.9, n = 6 yr). Average number of fledged young/successful nest was similar across years and sites: southeastern Ontario (2.8 young ± 0.36 SD, n = 3 yr) (6), and western New York (2.3), eastern Kansas (2.7 young ± 0.25 SD, n = 3 yr), central New York (2.7 young ± 0.19 SD, n = 12 yr), and eastern Oregon (2.8 young ± 0.27 SD, n = 10 yr) (MTM, unpublished data). In all locations, starvation was relatively uncommon, and most nests were lost to predators.

Information on lifetime reproductive success (LRS) not calculated for males because frequent loss of paternity with social partner and gain of paternity with extra-pair mates (1, 2) obviate the ability to measure true LRS. Estimates of LRS obtained for 159 females from central New York banded between 1989 and 1999 and followed to 2001 (177). LRS likely underestimated because some females first captured and banded after they had already produced young in a previous year (especially at start of study) and 5 females still alive at the end of study in 2001. LRS averaged 4.4 young ± 3.56 SD, but varied from 0 to 19 young/female. Female LRS exhibited a peak at 0 and 3 young (reflecting 1 year of unsuccessful or 1 year of successful breeding) and then declined exponentially from 3 to 19 (177). Very large differences in LRS of females highlighted by fact that 11% of females produced no young over their life, while 50% of young produced by 21.5% of females; most productive 10% of females produced 29.9% of young.

Length of life varies greatly among females, and variance partitioning indicated that length of life accounts for most differences in LRS, followed by positive contributions to LRS by proportion of eggs to yield fledged young (P), with a small contribution also from clutch size (177). Body size was not directly related to differences in LRS, but large females had lower P because they experienced more frequent nest depredation and laid smaller clutches (177).

Number of Broods per Season

One brood per season (see Breeding).

Life Span and Survivorship

Studies in central New York and eastern Oregon yielded very similar estimates of annual adult survivorship and suggest that ca. two-thirds of Eastern Kingbirds survive annually (151, 13, 148); survivorship estimates at both sites were based on resightings of color-banded individuals and Cormack-Jolly-Seber estimates that accounted for resighting probability (178). However, because detectability of Eastern Kingbirds is high (≥ 90% for males and ca. 84% for females) (151, 148), use of return rate and enumeration methods yields survival estimates that are very similar to Cormack-Jolly-Seber methods (13, 148). Survival not negatively affected by blood sampling for parentage analyses; if anything, bled females survived better than unbled females (179). Males in poor body condition during breeding tend to have higher probability of dying than other males (23). Female survival was slightly, but not significantly lower in New York, possibly reflecting a cost of reproduction (23, 13), but survival rate of sexes identical in Oregon (148).

In central New York, most males (63.0% of 143) and females (72.8% of 158) lived for just 2 yr, yielding mean life spans of 2.5 yr ± 1.79 SD and 2.2 yr ± 1.63 SD, respectively, and maximum life spans of 10 yr and 9 yr, respectively (147). For females that survived to a second breeding season, life span averaged 3.3 yr ± 1.63 SD (177). Hence, if a female survives to a second breeding season she can reasonably expect to breed for several years and a 4–5 yr lifespan is not unusual. Slightly lower estimated length of life of females is likely an artifact of greater dispersal tendencies of females (151, 15, 147), and the inability to distinguish permanent emigration from death.

In Ontario, return rates of breeding Eastern Kingbirds that were banded as adults (males 42%, n = 12; females 44%, n = 18) (7) were lower than other figures reported above; this was probably an artifact of smaller sample sizes and short length of study.

Juvenile (first-year) survival unable to be measured in central New York because of extremely low natal philopatry, but the isolation and ecological setting of eastern Oregon study site resulted in high natal philopatry (22.4% of fledged nestlings returned to the study site). Cormack-Jolly-Seber estimates of juvenile survival of 29.1% best viewed as a minimum estimate because detectability of juvenile males (0.676) and females (0.396) substantially lower than adults (148).

Disease and Body Parasites

Not known, except nestlings occasionally experience infestations of an ectoparasitic blood-feeding mite (species unknown). Effect of mites is to depress growth or cause nestlings to leave nest prematurely (and often die as a result). Most mite infestations occur as isolated cases, but occasionally many nests are affected (MTM). Eastern Kingbird is type host of mite (Boydaia tyrannis) that was recovered from the nasal cavity of an adult Eastern Kingbird in Michigan (180).

Causes of Mortality

Predators are main cause of egg, nestling, and fledgling mortality; avian predators are most important. Nestlings in many nests are very exposed and some occasionally die of exposure to sun or precipitation (165). Main cause of adult death is unknown, but presumably predation by accipiters and falcons is important (see 143 for other Tyrannus as prey). No information on predator pressure in South America. Late-spring storms during migration may cause deaths (29). Although death as a consequence of collisions with automobiles is not as frequent as in many other species (181), it is not an infrequent event among pairs that nest near roads (MTM).


Initial Dispersal from Natal Site

Young remain with parents on or near natal territory until late summer and then (presumably) begin southward migration. Natal philopatry is low in most populations: 4 of 259 (1.5%) nestlings in Ontario (7), 8 of 428 (1.9%) in New York (MTM), and 2 of 62 (3.2%) in British Columbia (M. Funk, personal communication). However, the unique ecological setting of a study site in eastern Oregon resulted in high natal site fidelity 82 of 366 (22.4%) banded nestlings returned; natal philopatry of males (50 of 195) was slightly, but not significantly higher than that of females (32 of 171) (148).

Fidelity to Breeding Site and Winter Home Range

Attachment to breeding site high and stronger in males than in females (151, 15, 147). In central New York, a new territory was used only 39 of 211 times that males returned from migration (i.e., 81.6% of males site faithful); females dispersed 64 of 189 possible times (i.e., 66.1% of females site faithful) (147). Nest failure tends to increase the chance that female will move to new territory (151), but for both sexes, individuals with low average annual reproductive success more likely to have dispersed at some point in their lifetime (147). Breeding dispersal occurs at any age, and as a consequence nearly half of females and a quarter of males disperse at least once in their lifetime (147). Dispersal in eastern Oregon usually to a location where conspecific reproductive success in past year was high (15). Breeding performance in southeastern Ontario appears to improve with territory quality (7), but in central New York territories do not exhibit consistent differences in productivity (160). In eastern Oregon, large scale nest failure due to nest predation appears to lead to abandonment of otherwise suitable habitat for many years (15).

Fidelity to overwintering range is unknown, but the 1 male Eastern Kingbird (of 6 carrying archival geolocators) that did not exhibit intratropical migration (i.e., long-term use of 2 overwintering sites), who also happened to be the only bird with 2 years of data, spent both overwintering periods in the same region of northwestern South America (3).

Dispersal from Breeding Site or Colony

Uncertain, but given long period of post-fledging parental care (21), parents and offspring probably gradually drift off territory together. Unknown whether migration initiated as a unit or separately.

Home Range

Although quantitative data not available, territory and home range size vary with habitat (MTM). Eastern Kingbird pack densely in riparian habitats in both eastern and western North America, but are more dispersed and potentially larger in fragmented eastern North American habitats that reduce territorial interactions. Territories tend to be larger during nest-building and incubation than later (146). Mean size of 4 territories in South Carolina during nestling period was 8.4 ha (range 5.7–14.2) (146). Most activities occur on territory, but breeding adults sometimes fly long distances out of territory. Home range is thus larger than territory, but no data on size of home range.

Population Status


Abundance varies greatly across range (see Figure 9). Highest values found in Great Plains near the center of the distribution, especially Kansas, Nebraska, and South Dakota, and North Dakota. Next greatest abundance to the northwest into Montana and Prairie provinces (Manitoba, Saskatchewan, Alberta) and southeast through Iowa, Missouri, and the Mississippi Alluvial Valley into the southeastern United States. Northeastern portion of range (northeastern U.S. and southeastern Canada) of generally lower abundance except for pockets in southeastern Ontario and Upper Peninsula of Michigan (182).

Using data from the North American Breeding Bird Survey (BBS), the mean annual population of Eastern Kingbirds was estimated at 26,000,000 individuals for the United States and Canada for the period between 2005 and 2014 (183). Point-count survey data collected by breeding bird atlas projects yielded estimates of annual population size of 300,000 for Ontario, 2001–2005 (67), 105,000 (95% CI: 95,000 to 115,000) for Ohio, 2007–2011 (184), and 110,000 (95% CI: 102,000 to 120,000) for Pennsylvania, 2004–2009 (185). Earlier estimates were higher for Illinois in 1957 (CI: 226,000 to 307,000; 144) and North Dakota in 1967 (356,000, 95% CI: 277,000 to 436,000) (186) probably reflecting true geographical differences in abundance and ongoing decline in numbers (see Trends).


Second breeding bird atlas projects reported declines since the 1980s in the percentage of atlas blocks occupied in various provinces and states, including New York (187), Ontario (67), Vermont (188), but either no decline in Maryland (189) or only a slight decline in Pennsylvania ( 185), Ohio (184), and others.

Analyses of Breeding Bird Survey (BBS) data (182) indicate that between 1966 and 2015 the continental population declined -1.28%/yr (95% credibility interval [CI]: -1.44 to -1.13), a decline that included the decade from 2005 to 2015 (-1.13%/yr; 95% CI: -1.58 to -0.68). Over a 45-yr period (1970–2014), BBS data indicated that the range-wide population has declined by an estimated 38% (183).

From 2005–2015, declines were strongest in the eastern BBS region (-1.46%/yr, 95% CI: -1.88 to -1.03), intermediate in the central region (-1.05%/yr, 95% CI: -1.70 to -0.40), but possibly stable in the western region (0.48%/yr, 95% CI: -0.84 to 1.87). From 2005–2015, significant and nonsignificant negative trend estimates were detected for 21 and 24 provinces/states, respectively, while nonsignificant positive trend estimates exist for only 5 provinces/states (British Columbia, Saskatchewan, Wyoming, North Carolina, Pennsylvania); no province or state exhibited a significant positive trend estimate. Given the preponderance of negative trend estimates (2005–2015), it is not surprising that 13 and 10 physiographic regions exhibited significant or nonsignificant negative trend estimates, respectively; the single physiographic region exhibiting a nonsignificant positive trend was the Northern Rockies. Like other aerial insectivorous bird species (28), especially those in northeastern North America, the Eastern Kingbird is exhibiting strong range-wide population declines.

Population Regulation

An 8 yr population study in Ontario suggested stable population size (7), but 10 yr studies in central New York (14, 190) and eastern Oregon (148; MTM, unpublished data) documented significant population declines. Causes of the declines are likely different, and in central New York probably reflect region-wide declines. On a local level, population size in central New York increased after years of either high nestling productivity or high adult survival (14). Nestling production varied considerably among years but there was no tendency to increase or decrease over time. Lower apparent adult survival in later years of study probably related to declining habitat quality resulting from habitat succession, which likely led to more frequent permanent emigration (i.e., “death”). Increasing forest cover probably contributes to widespread declines of Eastern Kingbirds in eastern North America. Eastern Kingbirds appear to be relatively long-lived, and population stability and persistence probably depends more on adult survivorship than offspring production as even small changes in adult survival can cause populations to shift between source and sinks (190).

Decline of populations in eastern Oregon is unlikely related to variation in adult survival as survival remained stable over time (148). Moreover, population trends (2005–2015) for the physiographic region (Great Basin; -0.30%/yr, 95% CI: -2.09 to 1.59) and state (-0.39, 95% CI: -4.98 to 4.65) within which the study took place did not differ from zero (i.e., stability; 182). Instead, declining annual production of young due to heavy nest mortality seems the most likely driver of population decline (MTM, unpublished data). Local phenomena, possibly increases in corvid populations, appear responsible for the decline.

Physical factors (e.g., storms, drought) probably have little influence on adult mortality except possibly during migration or early spring after return from migration. Relative importance of predation, competition, and disease or parasitism for adult mortality unknown. As few adults disappear during breeding, adult survival more likely a consequence of events experienced during migration and/or on wintering grounds, although carryover effects from breeding (23, 13) likely contribute. Although forest succession in eastern North America likely an important contributor to declines in that region, the range-wide decline suggests that other factors, acting during migration or on the wintering grounds, may also have important influences on changes in population size. No data are available for these periods.

Recommended Citation

Murphy, M. T. and P. Pyle. 2018. Eastern Kingbird (Tyrannus tyrannus), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.