SPECIES

European Bee-eater Merops apiaster Scientific name definitions

Hans-Valentin Bastian and Anita Bastian
Version: 2.0 — Published January 14, 2022

Plumages, Molts, and Structure

Plumages

Juvenile

As per (3, 1):

Juveniles are recognized by their dull green feathers on the nape, upperparts, and wing coverts, a “V” mark formed by the scapulars, a light green back and rump, and dark brown iris.

Head: Chin and throat yellow with small white feathers. The throat is bordered by a gray-black ring. The forehead and supercilium are turquoise, and the eye stripe is black. The ear coverts are black with a slight greenish tinge. The crown is chestnut brown and the neck reddish brown, which transitions into green on the back.

Body: Predominantly greenish turquoise; rump turquoise; mantle is olive in color overall, but with a semi-oval shape that extends over the middle of the mantle, which is green at the center and changes to straw yellow around the outer edges. Breast dark turquoise, belly turquoise, and the vent is whitish gray

Wings: The secondaries are chestnut brown to the base of the inner web, with a greenish-brown outer web; the distal quarter of the secondaries are blackish with a partial green edge. The primaries are dark. The outer webs of P1–P6 are green gray in color, and become increasingly green towards the outer primaries. The transition from S1 to P1 is marked by a color change of the inner webs from chestnut brown to gray. From P7 to the outermost primary, the outer webs are increasingly colored blue. All wing coverts are narrowly edged with yellow or white. The lesser and median coverts, and the alula, are green. The greater coverts are green brown, and the primary coverts are turquoise. Lesser and median underwing coverts are rusty brown to ochre in color; greater underwing coverts are light brown.

Tail: Dark from below and above; the inner webs are blue turquoise, the outer webs green turquoise. All tail feathers are the same length, lacking the elongated central tail feathers of adults. Undertail coverts are light blue turquoise.

Sex differences: Some juveniles can be sexed by plumage characteristics. Males can have more chestnut on the crown and nape, pale golden upperparts, and median wing coverts and secondaries tinged chestnut; females can have more greenish on the crown and nape, greenish upperparts, and median wing coverts and secondaries that are dull green. Based on a small sample size, significant correlations between sex and plumage coloration of juveniles were found in a Slovakian colony (4). In approximately 75% of the cases, color was a correct predictor of sex with yellowish-brown back feathers in male juveniles and greenish back feathers in female juveniles. The results of a GLM using a logistic regression analysis indicated that the condition of juveniles (body mass) is lower when plumage coloration and sex do not match (4).

In the second year, the plumage is no longer different from adult birds in most aspects, including the elongated central tail feathers. However, two-year-old birds can be separated from older ones by the worn brown (or faint blue) primary coverts, which contrast sharply with the bluish-green greater, median, and lesser secondary coverts (1).

Adult

"Definitive Basic" plumage of Humphrey and Parkes (5) and Howell et al. (6; Basic; 7).

Male.

Head: Chin and throat yellow, bordered above by a narrow light blue line, which transitions to white below the ear coverts, and bordered below by a black ring around the throat. The lores, eye stripe, eye-arcs, and ear coverts are black, with a narrow pale blue or greenish-blue border along the lores. Forehead white (often with some yellow-pointed feathers); across the back of the forehead patch, along the border with the front of the crown is a line of green feathers. Crown and neck vividly chestnut-brown, becoming slightly lighter towards the upper back.

Body: Upperparts, from the rear crown and neck down is chestnut brown, which rather sharply transitions to yellow gold on the back and rump. Scapulars with light brownish to yellow-gold inner webs and pale yellowish outer webs. The breast and belly are (greenish) blue to turquoise green.

Wings: Primaries are greenish blue with dull black tips and wide pale brown-gray inner webs. Secondaries reddish brown to chestnut brown and tipped with dull black; an approximately 1.5 mm narrow green stripe separates the brownish base from the black tips . Alula and greater coverts green with green-blue webs. Primary coverts green blue or green; greater, median, and inner lesser coverts (yellowish) chestnut brown on both webs of the feathers; outer lesser coverts green. The underside of the primaries is light gray with white shafts; underwing coverts beige to brownish yellow; axillaries somewhat more vivid, with greenish tinted basal half.

Tail: Tail feathers dark green with green-blue outer webs; T2–6 also have green-blue inner webs. The extended central feathers have a black shaft patch. Upper tail coverts dark green with green-blue feather edges. Undertail coverts light gray with white shanks.

Female. Similar to male, but with some diagnostic differences. Females can be distinguished by the more greenish shoulder-feathers, more green in the lesser wing coverts, and the usually paler yellow throat which is typically bordered by a narrower black ring (8). Typically, females have no or very little chestnut brown, but more pale golden brown on the wings. Greater and median coverts are light brown with a small greenish-blue margin, while the inner side of greater covert feathers are green (1). Lesser coverts are greenish with no or only little yellowish-gold coloration. The extent of the brownish and greenish coloration varies greatly in females, therefore, some birds cannot be sexed by wing coloration alone.

Eclipse Plumage

"Definitive Alternate" plumage of Humphrey and Parkes (5) and Howell et al. (6).

After the post-breeding molt, adult birds acquire a not well-known eclipse plumage, which is like the breeding plumage but with more greenish body feathers in both sexes; plumage patches that change include the addition of feathers with blue-green tips in the brown crown plumage, a yellowish-green shoulder, and the back with copper-brownish feather bases in some parts. The black edge of throat is often somewhat weaker and more blurred in this plumage as well (7, 8).

Aberrant Plumages

Occasionally, adult birds are seen with a dark green mantle and a light green back, as well as dark green inner primaries and greater coverts (8). Occasionally, light golden-green, yellowish-brown, or grayish-blue juveniles without a black throat border also occur (2; photo in 8). Such birds probably avoided the prenuptial molt of the coverts, and started molting into the eclipse plumage in early June (8).

Molts

Post-juvenile Molt (Preformative Molt according to 6)

"First Prebasic" molt of Humphrey and Parkes (5). First-year birds from Europe perform a post-juvenile molt in Africa between October and February. There is no known interruption of molt in young birds. During this incomplete molt, first-year birds replace the primaries, but not the corresponding coverts (9, 10, 11).

Pre-breeding Molt (Definitive Prebasic Molt according to 6)

Adults from the second year onwards replace some of their innermost primaries in Europe as early as July, interrupt their molt for the time they are migrating, and continue on the non-breeding areas, with a peak in October and November (9). In the Camargue (France), a third of the adults in August had already started molting the primaries (7); in August/September 70% of the migrating adults in Kazakhstan (12) and 79% in Spain had started molting the primaries (13). The molt suspension can last 1–2 months (9). In April/May of the following year, the earlier molted innermost primaries of adults are somewhat more worn than the others (9). Because first year birds replace all primaries on their non-breeding grounds, differentially worn primaries can be used in spring to distinguish adults from birds in their first year. During this molt, adult birds replace their primary coverts in sequence with the primaries. This is different to birds in their first year, which replace only their primaries in the non-breeding areas, but not the corresponding coverts. The difference in wear and coloration of the greater coverts to primaries makes it possible to distinguish second-year birds from older birds (9).

Tail feathers are usually replaced on the wintering grounds at the same time primary molt occurs (7). The tail feathers are generally replaced centrifugally from T1, with exception of T6, which is usually replaced before T5 and sometimes even before T4 and T5, and not infrequently before T4.

From birds in aviaries, it is known that they perform a body-feather molt in autumn and spring (8). In August, the body feathers grew in about half of birds captured in the Camargue (southern France) (7). In fall, this molt results in a little-known "eclipse" plumage, which only differs slightly from adult basic plumage (7, 8). Whether juvenile birds also molt body feathers around the same time as the very incomplete post-breeding body-feather molt of adults needs to be clarified.

Birds breeding in southern Africa molt in the middle of the year, at a similar time when the suspended molt of Palearctic birds begins (14).

Bare Parts

Bill

The bill is black.

Iris and Facial Skin

In adults, iris is reddish. In juveniles, iris is dark brown.

Tarsi and Toes

Feet are pinkish red in the first days of life, gray before fledging, and crimson brown in adults. The feet are distinctly short, and have a syndactyl toe arrangement, as is common to the Coraciiformes. As such, the outermost toe is adnate with the middle to the second; the first toe (digit I) faces backwards (15).

Measurements

Male bee-eaters tend to be larger than females. However, bee-eaters from Germany and Portugal did not differ in size. Morphometrically, the sexes are best be distinguished in a discriminant analysis using wing length, head-beak length, and tail-tip length (16).

Linear Measurements

Body length, from the bill to tail tip is 25–29 cm.

Wing Length

Based on 14 studies with a total of 1,531 individuals from southern, eastern, and central Europe as well as northern Africa (17, 18, 19, 20, 21, 8, 22, 23, 24, 16, Bastian and Bastian, unpublished), the mean wing length is 145–150 mm, with a range of 134 to 159 mm (Table 1). Males tend to have longer wings, measuring 3–6 mm longer on average (Table 1). According to seven studies with a total of 913 birds, the length of the third primary (P3) is on average 105–111 mm, with a range of 97–120 mm and with longer P3 in males (Table 2).

Bill Length

The bill is 29–35 mm long with a range of 28 to 44 mm (18, 20, 21,22, 16, Bastian and Bastian, unpublished). Minimum values may not be entirely accurate and may be the result of wear on the bill during nest construction, when bill length can be reduced by a third; after one month, the bill will grow back to its original pre-construction length (Table 3; 21).

Tail Length

The tail length varies between 97–116 mm, with slightly longer tails in males. However, this difference is based solely on different lengths of the tail tips (streamers); R6 is equally long in both sexes, 80–90 mm. Male streamers are significantly longer than those of females; when measured as the difference between R6 and R1, male streamer length is 22.2 +/-3.8 mm (n = 34), and female streamer length is 17.0 +/-3.0 (n = 30) mm (Bastian and Bastian, unpublished).

Mass

The body weight during the breeding season is usually about 50–57 g, but there is a lot of variation, and across the year can range from just over 40 g to almost 70 g (17, 18, 19, 20, 21, 22, 23,24, Bastian and Bastian, unpublished), according to age, sex and season, with males often slightly heavier than females, but with a large amount of overlap (Table 4a). In the Camargue (France), both sexes became continuously heavier during the breeding season; males went from 55.9 +/-4.6 g in May to 58.9 +/-2.8 g in August, and females from 54.4 +/-4.2 g (May) to 57.0 +/-4.8 g (August), but again with a large amount of overlap between sexes and months (7). During the early breeding period in Sicily, the weight of the adults increased by 7–18%, but while feeding nestlings, body mass decreased significantly, in males by 10%, and in females by up to 25% (21). Birds are lightest during spring migration, when they can be just over 40 g, and in extreme cases even lighter (17, 24). In Israel, out of 2,418 bee-eaters caught during spring migration, the body weight increased significantly along a 320 km south-north transect. It was assumed that birds in poor body condition rested immediately after crossing the North African deserts, but that birds in better condition rested later, which explains the trend of increasing body mass towards the north (25).

Recommended Citation

Bastian, H.-V. and A. Bastian (2022). European Bee-eater (Merops apiaster), version 2.0. In Birds of the World (S. M. Billerman and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.eubeat1.02