Eight of 38 nests started in 1960 were never completed (Table 6). Six of these abortive attempts were abandoned during, or shortly after, the completion of the suspension apparatus. Five of these nests were abandoned because the female did not begin building following the end of work by the male. The early abandonment of the other three nests 1-a (1960), 2-c (1960) and 6-e (1960) was attributable to the interruption of building by the male because of heavy rain and protracted territorial conflicts. The occurrence of these abortive nests at any time within the nesting efforts of a single pair indicates that such attempts are not examples of "false nestbuilding."
Renesting
Renesting after desertion or successful fledging occurs within two to thirty-six hours. Young were fledged from 1-a (1959) on June 19, 1959, and nest 1-b (1959) was discovered when late in the second phase of construction on June 22. If the nest was started on June 20, then renesting took place within 15 hours after fledging.
The Nest
Several authors have described various aspects of the nest of the Bell Vireo, notably Goss (1891:535); Simmons (in Bent, 1950:256), Nice (1929:13) and Nolan (1960:230-231). I can add but little to these descriptions.
The nest itself is a compact structure composed of strips of bark and strands of grasses that are interwoven and tightly bound with animal silk. The floor of the cup is first lined with a layer of small leaves and then the entire interior is lined with fine stems or strips of bark. Feathers are occasionally used to pad the bottom prior to lining, as are pieces of wool and milkweed down. Nest 2-e (1960) had been packed with small pieces of soil bearing moss prior to lining.
Table 6. Abortive Nesting Attempts in May and June of 1960.
| Nest | Length of time worked on | Cause of abandonment |
|---|---|---|
| 1-a | 1 day | Heavy rain |
| 1-h | 2 days | Female failed to build |
| 2-a | 1/2 day | Female failed to build |
| 2-c | 1 day | Protracted territorial dispute |
| 4-a | 1 day | Female failed to build |
| 5-a | 1 day | Female failed to build |
| 6-c | 1 day | Heavy rain |
| 7-a | 2 days | Female failed to build |
Early nests tend to be bulkier, having thicker walls and bottoms than later efforts. However, nests in May were found to have 16 per cent thicker bottoms and 41 per cent thicker walls than nests in June (Table 7). Standard nest measurements do not show this to be so, for the exterior and interior diameters at the rim are governed by the angle between the two branches of the fork.