vcdExtra (version 0.6-5)

Cormorants: Advertising Behavior by Males Cormorants

Description

Male double-crested cormorants use advertising behavior to attract females for breeding. In this study by Meagan Mc Rae (2015), cormorants were observed two or three times a week at six stations in a tree-nesting colony for an entire season, April 10, 2014-July 10, 2014. The number of advertising birds was counted and these observations were classified by characteristics of the trees and nests. The goal is to determine how this behavior varies temporally over the season and spatially, as well as with characteristics of nesting sites.

Usage

data("Cormorants")

source

Mc Rae, M. (2015). Spatial, Habitat and Frequency Changes in Double-crested Cormorant Advertising Display in a Tree-nesting Colony. Unpublished MA project, Environmental Studies, York University.

Details

Observations were made on only 2 days in weeks 3 and 4, but 3 days in all other weeks. One should use log(days) as an offset, so that the response measures rate. Cormorants$days <- ifelse(Cormorants$week %in% 3:4, 2, 3)

Examples

data(Cormorants)
str(Cormorants)

library(ggplot2)
ggplot(Cormorants, aes(count)) + geom_histogram(binwidth=0.5) + 
	labs(x="Number of birds advertising")

# Quick look at the data, on the log scale, for plots of `count ~ week`, 
#   stratified by something else.
library(ggplot2)
ggplot(Cormorants, aes(week, count, color=height)) + geom_jitter() +
	stat_smooth(method="loess", size=2) + scale_y_log10(breaks=c(1,2,5,10)) +
	geom_vline(xintercept=c(4.5, 9.5))

# ### models using week 
fit1 <-glm(count ~ week + station + nest + height + density + tree_health, data=Cormorants,
    family =  poisson)

library(car)
Anova(fit1)
# plot fitted effects
library(effects)
plot(allEffects(fit1))