Birth Number and Intervals

turtles-own [age female monthspreg miscarriagenum birthnum]

to setup
  clear-all
  create-turtles 11 [ setxy random-xcor random-ycor ]
  set postpartum_infertility 8
  set marriage_age 15
  set perc_female_at_birth 49
  set fertility 20
  set runlength 55
  set perc_miscarriage 20
  set life_expectancy 45
  ask turtle 10 [set age -24 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 9 [set age 0 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 8 [set age 264 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 7 [set age 192 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 5 [set age 192 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 6 [set age 168 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 0 [set age 192 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 1 [set age 216 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 2 [set age 240 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 3 [set age 264 set female 1 set monthspreg -1 set birthnum 0]
  ask turtle 4 [set age 288 set female 1 set monthspreg -1 set birthnum 4]
  reset-ticks
end 

to go
  tick
  if ticks >= (runlength * 12) [ stop ]
  ask turtles [increment-age]
  ask turtles [increment-monthspreg]
  ask turtles [conceive]
  ask turtles [miscarry]
  ask turtles [birth]
  ask turtles [dopostpartum]
  ask turtles [check-death]
                 ;; increase the tick counter by 1 each time through
end 

to increment-age
  set age (1 + age)
end 

to increment-monthspreg
  if monthspreg > -1 [
      set monthspreg (1 + monthspreg)]
end 

to conceive
    if random 100 <= fertility and monthspreg = -1 and female = 1 and age >= (marriage_age * 12 ) and age <= 540 ; 15-45
      [set monthspreg 0  ]
end 

to miscarry
    if random 100 < perc_miscarriage and monthspreg = 5 and female = 1
    [set monthspreg -1 set miscarriagenum (1 + miscarriagenum)]
end 

to birth
  if monthspreg = 9 and female = 1 and random 100 >= infant_mortality [
    hatch 1 [
      set birthnum (1 + birthnum)
      set age 0
      setxy random-xcor random-ycor
      ifelse random 100 < perc_female_at_birth [set female 1] [set female 0]]
    ]
end 

to dopostpartum
  if monthspreg = 9 + postpartum_infertility
  [set monthspreg -1]
end 

to check-death
    if age = (life_expectancy / 12) [ die ] ;; Dies once they hit life expectancy
end