Stay or go? Changing breeding conditions affect sexual difference in colony attendance strategies of Atlantic puffins Fratercula arctica

Male and female birds have different interests in reproductive investment, which in turn may increase negative effects of poorer breeding conditions caused by e.g., climate change or ecosystem regime shifts. Using a 33-year time series with resightings of Atlantic puffins Fratercula arctica individually colour-ringed as breeders in previous years, we show that the difference in colony attendance of male and female birds depends on the environmental conditions for raising young, proxied by the average duration of the chick period and size of the herring Clupea harengus fed to the chicks in the colony each year. The longer the chick period, and thus the birds’ overall investment in reproduction, the more was the sex ratio of adults sitting out on the colony surface biased in favour of males. An increase in herring size, indicating better feeding conditions for raising chicks, led to more observations of both sexes, and the increase was slightly more prominent for females than males. We di..., The attendance data were collected by capture-mark-resighting (CMR) of adult breeding Atlantic puffins in a colony in North Norway. The birds were sexed by DNA (blood sample), and time since ringing was used as a proxy for their age. Mean dates of chick hatching and chick death or nest departure were estimated from monitoring the content of on average 103 (range 34-284) individually marked active nest-burrows in the same colony throughout the chick period. The length of their main prey, age 0 herring, was calculated from identifying and measuring all fish sampled in on average 75 (range 0-266) food loads collected by mist-netting adults on their way to the nest. In years with no food sampled, herring size was estimated from its realtionship with ICES recruitment indices for the Norwegian spring-spawning herring stock 2 years later. , , # Changing breeding conditions affect sexual difference in colony attendance of Atlantic puffins Fratercula arctica

[https://doi.org/10.5061/dryad.v15dv423w](https://doi.org/10.5061/dryad.v15dv423w)

## Description of the data and file structure

The following parameter coding was used for the data analysis in Anker-Nilssen et al. \"Stay or go? Changing breeding conditions affect sexual difference in colony attendance strategies of Atlantic puffins *Fratercula arctica*\". The coding is also repeated on top of the accompanying data file, which is in simple text format with columns separated by semicolons.

Code: coded colour ring of individual puffin

Year: year of observations

Hatching_ref: Defines observation period - before or after hatching

Obs: Number of observations

Effort_hours: number of hours spent observing per year and period (Hatching_ref)

Sex: male / female

Age: Years since first ringed

Date_laying: average laying date for each year

Date_hatching: average hatching date...