FAMILY FORMICARIIDAE 147 



Male and female work at nest construction. A nest seen on Barro 

 Colorado Island, on the date mentioned above, placed 2\ meters 

 above the ground, was suspended by the rim from a fork near the end 

 of a leafy branch. Its resemblance to the nest of a vireo was only in 

 form of suspension as it was woven so loosely of fine rootlets and 

 other vegetable fibers that I could see the outline of the two eggs 

 from below. Externally it had long green mosslike tendrils draped 

 over it. Both male and female were observed in incubation. Another 

 nest, with a female in attendance but without eggs at the time, was 

 seen near Pucro, Darien, on February 3, 1964. This was only a meter 

 above the ground in open undergrowth at the side of a forest trail. 

 The open basket was suspended by the rim in the fork formed by 

 two twigs that crossed one another. It was rather wide and shallow, 

 woven of rootlets so loosely that in looking down into it I could see 

 through it to the leaves and twigs beneath. Externally it was decorated 

 with streamers of green moss. 



Skutch (Auk, 1934, p. 10; 1945, p. 18, Pac. Coast Avif., 1969, 

 no. 35, pp. 172-179) described the two eggs that constitute a set as 

 white, heavily spotted with chocolate and umber, with the markings 

 forming a wreath around the larger end. He recorded the extremes in 

 size in six eggs as 22.6 X 16.7, 24.2 X 16.3 and 25.4 X 16.7 mm. Two 

 eggs collected by Carriker (Ann. Carnegie Mus. vol. 6, 1910, p. 603) 

 on the Costa Rican side of the Rio Sixaola, were described as creamy 

 white in color, heavily marked with reddish brown and lilac, with 

 measurements of 24.0x16.5, and 24.5x17 mm. R. A. Johnson 

 (Auk, 1953, p. 495) reported the incubation period as 14 days. Both 

 Skutch and Johnson describe the young at hatching as blind, without 

 down, and dark skinned. In the Canal Zone nesting is recorded to 

 extend from December to July or August. 



Though through much of its range this species and Thamnophilus 

 doliatiis are found in the same general areas, there appears to be no 

 active competition between them since the Slaty Ant-shrike is a true 

 forest inhabitant, while the Barred Ant-shrike is found along the 

 borders, in open thickets, or on the high open summit of the tree 

 crown, all habitats not attractive to the other species. A similar 

 division of habitat occurs in Darien where the Slaty Ant-shrike is 

 found with Thamnophilus nigriceps. It is interesting therefore to 

 note that the present bird does not penetrate the range of Bridges' 

 Ant-shrike, Thamnophilus hridgesi, which also extends into heavy 

 forest. 



On the Caribbean slope the subspecies atrinucha ranges north 



