SPECIES

Slate-throated Redstart Myioborus miniatus Scientific name definitions

William D. Harrod and Ronald L. Mumme
Version: 2.0 — Published July 29, 2022

Breeding

Introduction

Extensive data on breeding biology are available from two populations at 10º N latitude: Monteverde, Costa Rica (subspecies comptus; 8 ) and Yacambú National Park, Venezuela (subspecies ballux; 47).

Phenology

At 10º N latitude in both Costa Rica (subspecies comptus) and Venezuela (subspecies ballux), Slate-throated Redstart is a strongly seasonal breeder that initiates nests from late March through late June, with the peak of nesting occurring in late April and early May (8, 47). Limited data from northeastern Mexico and the rare instances of nesting in the southwestern United States suggest that breeding occurs primarily in May and June at the northern limits of the range (29, 30, 26, 33).

Limited data from equatorial regions suggest that breeding seasons are more extended. For example, nesting occurs from late December through July near Cali, Colombia (3.5º N; 48, 44, 45). In eastern Ecuador (1º S), the congeneric Spectacled Redstart (Myioborus melanocephalus) nests from May–December (49), suggesting that Ecuadorian populations of Slate-throated Redstart may also have a similarly extended nesting season. In a high latitude Bolivian population at 18º S, nest building has been observed in mid-October, and two nests with nestlings were found in early-November and mid-December (S. K. Herzog, unpublished data).

Nest Site

Nests are placed on the ground on steep slopes in undisturbed forests or in banks along roads and trails in areas of human activity; occasional nests are built among epiphytes on a fallen log or in the root mass of an overturned tree (50, 4, 51, 8, 47).

Nest

Construction Process

Females are usually solely responsible for nest construction. Skutch (50) reported one nest in Costa Rica at which both members of the pair appeared to participate in nest construction, but this observation is likely erroneous or exceptional; in more extensive studies in both Costa Rica (8) and Venezuela (47), only females engaged in nest building.

Structure and Composition

The nest is a well-disguised domed nest, but some nests may lack a roof when the overlying vegetation provides a natural roof (50, 4, 51, 8, 47).

Dimensions

In Venezuela, nest exteriors averaged 64.8 ± 25.0 mm high and 103.9 ± 21.2 mm wide. Internal cup dimensions averaged 49.1 ± 4.7 mm across with a depth of 31.4 ± 9.5 mm (47).

Eggs

Size

Egg size in Costa Rica averages 16.7 x 13.4 mm, and neither length nor width is significantly related to laying order (8).

Mass

In Venezuela, mean egg mass is 1.6 g (range 1.2–1.9 g; 47).

Color and Surface Texture

Eggs are dull white with dark red or brown spots (47).

Clutch Size

Clutch size varies geographically. It averages 2.9 (range 1–4) in Costa Rica (8), but is substantially smaller in Venezuela, averaging 2.1 in Yacambú National Park (47) and 2.4 in Henri Pittier National Park (51). No information is available on clutch size from populations at either the northern (Mexico) or southern (Bolivia) limits of the breeding range.

Egg Laying

Eggs are laid early in the morning, usually within the first few hours after dawn. Eggs typically are laid on consecutive days (8).

Incubation

Onset of Broodiness and Incubation in Relation to Laying

Incubation does not begin until clutch completion (8).

Incubation Patches

Only females develop a brood patch.

Incubation Period

The incubation period in Costa Rica is 14–15 d (mean 14.2 d), but is somewhat longer and more variable in Venezuela (14–18 d, mean 15.3 d; 8, 47). No information is available on incubation period from populations at either the northern (Mexico) or southern (Bolivia) limits of the breeding range.

Parental Behavior

Incubation is performed only by females. However, some males occasionally feed females on the nest; at 52 nests observed 6–8 h during incubation in Venezuela, 21 males (40%) fed their mates, averaging 0.1 feeding trips/h. Daily nest attendance by incubating females averaged 59% in Venezuela (47).

Hatching

Little detailed information, but eggs appear to hatch synchronously (8, 47).

Young Birds

Growth and Development

The nestling period is typically 11–12 d in both Costa Rica and Venezuela (8, 47). Nestling growth curves in Costa Rica and Venezuela appear to be very similar (51, 8, 47). Body mass averaged 10.8 g for Venezuela nestlings immediately prior to fledging (age 10 and 11 d), and nestlings reached mean adult body mass (9.5 g) 7–8 d after hatching at both locations (8, 47).

Parental Care

Brooding

Only females brood young (8, 47). In Venezuela, brooding attentiveness averaged 63% during the first three days after hatching but dropped to 11% after feather emergence. In Costa Rica, females ceased brooding 5–6 d after hatching.

Feeding

Both females and males provision nestlings and fledglings (8, 47; see Young Birds). In Venezuela, the average rate of provisioning was 3.8 feeding visits/h during the first three days after hatching, but the rate increased to 9.4 feeding visits/h after feather emergence (47). In Costa Rica, provisioning rates appear to be considerably higher, averaging 20.3 feeding visits/h when nestlings were 5–9 d old (8).

Cooperative Breeding

Not reported.

Brood Parasitism by Other Species

Not reported.

Fledgling Stage

Association with Parents or Other Young

Both parents continue to feed the young after fledging, and may do so at least until the young are 40 d old (28–29 d after fledging) (8).

Ability to get Around, Feed, and Care for Self

Juveniles begin to forage on their own when 30 d old (8).

Immature Stage

More information needed on immature birds after reaching independence.

Recommended Citation

Harrod, W. D. and R. L. Mumme (2022). Slate-throated Redstart (Myioborus miniatus), version 2.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.sltred.02