# High spatial pair cohesion during and after breeding in a socially monogamous territorial passerine

## TL;DR

This study shows that socially monogamous birds, like chirruping wedgebills, stay closely coordinated with their partners during and after breeding, suggesting pair bonds serve functions beyond reproduction.

## Contribution

The study provides new empirical evidence of high spatial coordination in a socially monogamous bird species using fine-scale tracking data.

## Key findings

- Pairs had extremely similar home ranges with a similarity index of 0.93 compared to 0.18 for non-pairs.
- Partners maintained closer proximity than expected by chance and followed each other frequently during and after breeding.

## Abstract

Long-term social monogamy, a prevalent mating system in avian species, is often associated with increased cooperation and coordination as well as reduced sexual conflict. Although many studies have highlighted the benefits of long-term partnerships for individuals, there remains a lack of insight into how closely partners associate with one another behaviorally. To date, studies investigating pair cohesion in seasonal and long-term partnerships are typically restricted to arrivals at the nest or feeding sites during the breeding season. Using fine-scale automated tracking data on chirruping wedgebills (Psopodes cristatus), a territorial socially monogamous species, we characterized how partners coordinate their movement during and after the breeding season. We used 12 pair-bonded individuals with consistently high localization rates that were tracked for a period between 32 and 69 days, with an average of 260,000 localizations per individual. We demonstrate that pairs (1) had extremely similar home ranges with a similarity index of 0.93 versus 0.18 for non-pairs, (2) maintained consistently closer proximity than expected from movement without paying attention to a partner, and (3) followed each other as they moved, with individuals following their moving partner in 42% of cases during and in 47% of cases after breeding. Our findings show that pair cohesion in socially monogamous territorial species can be very high in both a breeding and non-breeding context, illustrating that strong coordination among partners has important functions beyond reproduction and parental care.

Many birds form lasting partnerships, suggesting that spending time with one's partner is very beneficial. Still, we know surprisingly little about their close associations. We studied the movement of chirruping wedgebills and found breeding partners used almost the exact same areas, were consistently close to each other, and follow each other frequently during and after breeding. Overall, being with one's partner is important beyond reproducing together, and partnerships go beyond the requirements for current reproduction.