Host response to conspecific brood parasitism in colonial Red-breasted Mergansers (Mergus serrator): Positioning of parasitic eggs within the clutch

Brood parasitism can be costly to host fitness, which in turn may favour host strategies that decrease these costs. Duck (Anatinae) nests are often parasitized by eggs of other ducks, and one way that hosts can respond to potentially costly brood parasitism is to move parasitic eggs to the periphery of clutches where egg incubation temperatures can be suboptimal relative to the central region of clutches. We explored whether Red-breasted Mergansers (Mergus serrator) use discriminatory egg incubation against parasitic eggs laid by conspecifics in a population where conspecific brood parasitism (CBP) is common. We used isoelectric focusing electrophoresis of egg albumen from entire clutches of 12 parasitized nests to identify parasitic eggs. A randomization test pooling identified parasitic eggs (n=50) across nests revealed that hosts did not position parasitic eggs along the periphery of clutches or out of the central region more than that expected by chance, and this was the case for pa..., , , # Host response to conspecific brood parasitism in colonial Red-breasted Mergansers (Mergus serrator): Positioning of parasitic eggs within the clutch

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

## Description of the data and file structure

Red-breasted Mergansers nests were located during 2022 and 2023 on the Tern Islands, Kouchibouguac National Park, New Brunswick, Canada. After being located, nests were visited twice each week until their fate was determined (Hatched or Abandoned). At the first visit to the nest, the eggs were assigned a number which was written on the egg and 2-3 cc of albumen was removed from each egg and run through a IEF gel pH 3-19 pre-cast gels, females were identified through distinct albumin protein band patterns. During each visit through incubation, we photographed clutches to record individual egg positions, and tracked the location of each egg.

### Files and variables

#### File: IEF\_Results\_RBME\_Albumin\_2022...,