Estimation of trade-offs between current reproduction and future survival and fecundity of long-lived vertebrates is essential to understanding factors that shape optimal reproductive investment. Black brant geese (Branta bernicla nigricans) are able fledge more goslings, on average, when their broods are experimentally enlarged to be greater than the most common clutch size of four eggs. Thus, we hypothesized that the lesser frequency of brant clutches exceeding four eggs results, at least partially, from a future reduction in survival, breeding probability, or clutch size for females tending larger broods. We used an eight-year mark-recapture dataset (Barker robust design) with five years of clutch and brood manipulations to estimate long-term consequences of reproductive decisions in brant. We did not find evidence of a trade-off between reproductive effort and true survival or future clutch size. Rather, future breeding probability was maximized (0.92 ± 0.03 [se]) for manipulated females tending broods of four goslings (i.e., the most common natural brood size) and lower for females tending smaller (one gosling; 0.63 ± 0.09 [se]) or larger broods (seven goslings; 0.52 ± 0.15 [se]). Our results suggest that demographic trade-offs for female brant tending large broods may reduce the fitness value of clutches larger than four and, therefore, contribute to the paucity of larger clutches. The lack of a trade-off between reproductive effort and survival provides evidence that this trait, to which fitness is most sensitive in long-lived animals, is buffered against temporal variation.
cs_initiation_date
This file contains data used to estimate the effects of clutch and brood size manipulations on clutch size and initiation date of female black brant in year t+1. Variable descriptions are as follows: "METAL" is the unique number on a female's steel leg band; "CSM1" is the laid clutch size of a female in year t -1; "CS" is the laid clutch size of a female in year t. "IDM1" is the initiation date, in Julian days, of the female's nest in year t - 1; "ID" is the initiation date, in Julian days, of a female's nest in year t; "MCSM1" is the manipulated clutch size of a female in year t - 1, this variable was z-standardized with mean = 0 and sd =1 to enable replacement of missing values with 0; "GLNM1" is the manipulated initial brood size of the female in year t - 1; "YEAR" represents breeding season t; "RELID" is the relative initiation date (Julian initiation date - median initiation date) of a female's nest in year t; "RELIDM1" is the relative initiation date of a female's nest in year t - 1.
mass_nthprim
This file contains the data for the analyses of nesting mass, change in mass between nesting and banding, and ninth primary length. Note the some nesting mass (nmass) data is blank when the change in mass variable (chng_mass) is not, this is because in this case the female did not undergo a clutch manipulation and therefore was not used in the nest mass analysis. The variables are as follows: "METAL" is the unique code on the female's steel band, "emcs" is the final manipulated clutch size a female incubated,"gln" is the initial brood size of the female, "nmass" is the mass (g) of the female if she was captured within 24 hrs of hatch and underwent a clutch manipulation, "YEAR" references breeding season t, "NINTHPRIM" is the length of a female's ninth primary feather on the day she was captured during brood rearing,"DSH" is the days between when a female's nest hatched and she was captured during brood rearing,"chng_mass" is the change in the mass of a female between hatch and when she was captured during brood rearing.
return_rate_data
This file contains the reencounter data used in the return rate (logistic regression) analysis. The variables in the file are as follows: "return" indicates if a female was seen nesting and/or captured at banding with a brood patch (return = 1) or not (return = 0); "gln" is the initial manipulated brood size of a female in year t -1.
cmr_file
This file contains the capture-mark-recapture data used to estimate the effects of clutch and brood size on adult female breeding probability and survival. Variables are as follows: "ch" is the capture histories, which are in an LDLD format with two secondary occasions (nesting and banding) each represented by "L", followed by non-breeding season (represented by second "D") reencounter data (0=not encountered, 1=encountered dead, 2=re-sighted alive), primary occasions are 2008-2015. Note that the first "D" in the capture history for each primary occasion is essentially a dummy variable, which are all "0". "mbha 2008:2012" indicates if a female's reproductive output was manipulated and she was captured and marked at the nest during that year; "age 2008:2015" is the z-standardized age (mean = 8.64, sd = 5.59) of a female in year t, "ageq 2008:2015" is the squared z-standardized age value for use in models with a quadratic effect of age; "emcs 2008:2015" is the z-standardized (mean = 4.22, sd = 1.87) final manipulated clutch size value in year t; "emcsq" is the squared z-standardized emcs value for use in models with a quadratic effect of emcs; "gln" is the z-standardized (mean = 3.49, sd = 1.73) initial brood size value for the female in year t; "glnq" is the squared z-standardized gln value for use in models with a quadratic effect of brood size; and "grp" is a grouping variable that indicates that all females were manipulated during our study. Note that for variables "emcs" and "gln" the years 2013-2015 have values that are all 0 but are needed because program Mark requires time varying covariates for each primary occasion. Zeros for other variables mean the female had not yet been captured and released or was not manipulated that year.
