Because we are interested in the qualitative effects of the contact–density functions rather than in detailed differences that are specific to the model system, we here report the results with a focus on the qualitative aspects of SIR dynamics and prevalence. The constant function resulted in a relatively low epidemic peak during the breeding season, while the other three functions showed a clear epidemic peak where prevalence (proportion Infecteds; figure 2, red curves) increased sharply for the linear and sigmoid functions, but more gradually for the power function. Median peak prevalence for the four functions: 45% (constant), 68% (linear), 60% (power) and 72% (sigmoid). The dynamics of the proportion of Recovered (immune–antibody-positive; figure 2, blue curves) individuals were highly similar for the four functions, although they did differ in how low the Recovered proportion becomes at the end of the birth pulse: 15% (constant), 2% (linear), 14% (power) and 0.5% (sigmoid). There was a steeper build-up of Susceptibles (figure 2, green curves) for the linear and sigmoid than for the other two functions, due to the fact that transmission rates started increasing later in the year (at higher densities). Figure 2.SIR dynamics for the four different contact–density functions. For each simulation run in which there was successful persistence, the 8th year was retained (days 3030 to 3395). The figure shows all these outputs plotted on top of each other. The increase in Susceptibles corresponds with the birth pulse. Infectious period 1/γ = 60 days, transmission rate p = 50, initial population size N0 = 100 000.