DOI: 10.5061/dryad.zgmsbccpk
title: Data from: Host response to conspecific brood parasitism in colonial Red-breasted Mergansers (Mergus serrator): Positioning of parasitic eggs within the clutch

description: 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 parasitic eggs laid prior to and after the onset of incubation.
 Similarly, nest-level analyses showed that parasitic eggs were random in
 all but the smallest clutch, which contained one identified parasitic egg.
 Thus, parasitic eggs were not moved to the periphery of heavily
 parasitized clutches, where egg temperature gradients between central and
 peripheral regions of nests are expected to be greatest. Only four eggs
 (&lt;0.5 % of 1,276 eggs) were found buried within nest bowls. Eggs
 that were removed from nests consisted of parasite and host eggs and were
 more likely along the periphery of clutches prior to their removal than
 that expected by chance. Our results indicate that discriminatory egg
 incubation of parasitic eggs is not a well-developed tactic for defending
 against CBP in Red-breasted Mergansers, though hosts may rely on certain
 cues to decide which eggs are to be removed from nests (e.g., addled
 eggs).
description: # 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\_2023.csv **Description:**  ##### Variables * nest_ID: The ID code used to identify nests between spreadsheets: nest_IslandNumber_NestNumber * island_num: The island where the nest is found: Island 1, 2 or 3 * nest_num: The nest number on the island, each island starts with nest 1 * date_sampled: The date on which the albumin was sampled: Year-Month-Day * year_sampled: The year the albumin was sampled * month_sampled: The month the albumin was sampled * day_sampled: The day of the month albumin was sampled * clutch_size: The maximum clutch present within the nest * egg_num: Number associated with the egg, used to identify albumin sample and egg position, starting at 1 in each nest. * hatch_Y_N: Did the egg successfully hatch: Yes or No * removed: Was the egg removed from the nest before or during incubation: Yes or No * burried: Was the egg burred within the bottom or side of the nest: Yes or No) * num_bands: The number of bands within the sample well in the IEF Gel * host_Y_N: Is the egg thought to be the hosts by shared a band pattern with the majority of the clutch * parasite_Y_N: Is the band pattern different from the host band pattern by not shared a band pattern with the majority of the clutch * egg_grouping: Identification of band pattern starting with nest number (Island number_nest number) followed by a letter, each letter represents a different band pattern within the clutch. The fist band pattern within a clutch starts with A and goes down the alphabet * num_females: The predicted number of females which laid eggs within the nest , minimum based on band pattern * notes: Any further notes #### File: egg\_position\_raw\_data\_RBME\_2022\_2023.csv **Description:**  ##### Variables * nest_ID: The ID code used to identify nests between spreadsheets: nest_IslandNumber_NestNumber * island_num: The island where the nest is found: Island 1, 2 or 3 * nest_num: The nest number on the island, each island starts with nest 1 * clutch_size: The maximum clutch present within the nest * nest_year: The year of when the nest was active * photo_num: The photo number with 1 being the first photo taken and n being the nth photo taken * photo_date: Date the photo was taken: year-month-day * photo_year: Year the photo was taken * photo_month: Month the photo was taken * photo_day: Day the photo was taken * egg_num: Number associated with the egg, used to identify albumin sample and egg position * h_location: Location of egg on the horizontal plane: 0 - Within the central region of clutch, 1- Between the central region and the periphery of nest, 2 - along clutch periphery, 3 - Outside of the nest * num_h_rings: The number of rings calculated within the picture: 1, 2 , 3 * v_location: Vertical location of the egg within the picture: 0 - the egg is underneath and fully covered by one or more eggs, 1 - the egg is underneath and partially covered by another egg, 2 - the egg is not covered and is not covering another egg, 3 - the egg is on top of and covering another egg. * removed: Has the egg been removed from the nest:N = No, Y = Yes, P= removed previously from nest * addeling: Is the egg visually addling in the photo,, includes observations of eggs which has been removed from the nest if located * burried: Are the eggs buried in the nest: Yes, No * added: Was the egg added to the nest * notes: Any further notes * in_out_ring: Is the egg on the inside or the outside of the nest: in, out * top_bottom_covered: Is the egg on the bottom, top or covered in the nest * parasite: Is the egg a parasitis egg, determined in IEF_Results