The benefits of pair bond tenure in the cooperatively breeding pied babbler (Turdoides bicolor)

Abstract

The benefits of stable pair bonds (that persist between breeding attempts) have been well described, but are relatively less well known in cooperatively breeding species. If pair bonds are beneficial, then it is possible that the bond between the behaviorally and socially dominant pair may influence factors such as reproductive success and group stability in cooperative species. Here, we used long-term data to investigate the relationships between pair bond tenure, reproductive success, and group stability in the cooperatively breeding pied babbler (Turdoides bicolor). Pair bond tenure positively influenced both the number of offspring recruited annually per pair and total reproductive success (over entire pair bond duration), indicating that pair bond tenure has an important influence on reproductive success. The likelihood of immigration into the group was lower for groups containing a bonded pair with long tenure, indicating that the duration of pair bonds may impact group stability. These findings suggest that pair tenure, a hitherto relatively unexplored factor in cooperative species, may have an important influence on group dynamics.

Keywords: cooperative breeding; pair bond; pair tenure; pied babblers; reproductive success.

Figure 1

A pied babbler pair allopreening before going to roost. Tactile affiliative interactions between individuals may serve to strengthen social bonds. Observations of behavior can be recorded at a distance of 1–2 m from these habituated birds. (Photo by EMWiley)

Figure 2

The frequency and distribution of known pair tenures in the pied babbler population, from 2003 to 2015

Figure 3

The relationship between chick recruitment (per year) and pair tenure. The fitted regression line is shown with shaded 95% confidence intervals. Data points are integers and have been jittered for better visibility

Figure 4

The relationship between the number of chicks (raised to 1 year of age posthatch) and the likelihood a pair persisted to the next year. A value of “1” on the y‐axis denotes persistence. The fitted regression line is shown with shaded 95% confidence intervals. Data points are integers and have been jittered for better visibility

Figure 5

(a) The relationship between reproductive success (total number of chicks reaching adulthood that a pair raise together) and complete pair tenure (total length in days). The fitted regression line is shown with shaded 95% confidence intervals. Data points are integers and have been jittered for better visibility. (b) The relationship between total reproductive success per hatched brood (over entire pair duration) and complete pair tenure (total length in days). The fitted regression line is shown with shaded 95% confidence intervals. Data points are integers and have been jittered for better visibility

Figure 6

The relationship between immigration events and complete pair tenure (total length in days). The fitted regression line is shown with shaded 95% confidence intervals. Data points are integers and have been jittered for better visibility