1. Long-lived monogamous species gain long-term fitness benefits by equalising effort during bi-parental care. For example, many seabird species coordinate care by matching foraging trip durations within pairs.

2. Age affects coordination in some seabird species; however, the impact of other intrinsic traits, including personality, on potential intraspecific variation in coordination strength is less well understood.

3. The impacts of pair members’ intrinsic traits on trip duration and coordination strength were investigated using data from saltwater immersion loggers deployed on 71 pairs of wandering albatrosses Diomedea exulans. These were modelled against pair members’ age, boldness and their partner’s previous trip duration.

4. At the population level, the birds exhibited some coordination of parental care that was of equal strength during incubation and chick-brooding. However, there was low variation in coordination between pairs and coordination strength was unaffected by the birds’ boldness or age in either breeding stage. Surprisingly, during incubation, foraging trip duration was mainly driven by partner traits, as birds that were paired to older and bolder partners took shorter trips. During chick-brooding, shorter foraging trips were associated with greater boldness in focal birds and their partners, but age had no effect.

5. These results suggest that an individual’s assessment of their partner’s capacity or willingness to provide care may be a major driver of trip duration, thereby highlighting the importance of accounting for pair behaviour when studying parental care strategies.

Description of methods used for collection/generation of data: Intrinsic variables: this population has been monitored since the 1960s and so data on the sex, age and partnership histories were available for all individuals.

Trip durations: 71 wandering albatrosses were tagged with saltwater immersion loggers across 7 years. The loggers distinguish between dry periods (land or flying) and wet periods (immersed in saltwater).

Boldness: Responses of incubating birds to an approaching human (from a 5m distance) were quantified using an ordinal scale from 0-5 (0 = no response; 1 = raises head; 2 = rises onto tarsus; 3 = vocalises; 4 = stands up; 5 = vacates nest). Higher scores = bolder birds.

Partner previous bout (part_prev_bout): the trip duration of each bird's partner immediately prior to their own foraging trip.

Methods for processing the data: Trip durations: Periods > 12 hours dry were considered to be nest attendance bouts. Periods in between these > 12-hour dry bouts were considered foraging trips. The length of these is the response variable individual trip duration (no_hours). Partner (unloggered birds) trip durations were estimated from the loggered birds nest attendance bouts. Incubation trips occurred between 16th Dec- Mid march (exact date varied depending on patterns for individual pairs). Brooding occurred between mid-march and April 11th each year.

Boldness scores: Observation number, observer identity, and bird ID were fitted as fixed effects in a generalized linear model. Individual parameter estimates were mean-centred at the population level (see Patrick et al., 2013 for a detailed description). This created a boldness score of each individual.

Software-specific information needed to interpret the data: Data processed in R, packages used: library(dplyr) library(MuMIn) library(ggplot2) library(lme4) library(tidyverse) library(optimx) library(knitr) library(car) library(effects) library(sjPlot)