Age‐specific response of a migratory bird to an experimental alteration of its habitat

Summary 1.  Recruitment, i.e. the influx of new breeding individuals into a population, is an important demographic parameter, especially in species with a short life span. Few studies have measured this parameter in solitary‐breeding animal populations even though it may yield critical information on habitat suitability and functional connectivity. 2.  Using a before‐after, control‐impact pairs (BACIP) experimental design, we measured: (i) the return rate and apparent survival rate of individually marked territorial males of a neotropical migrant bird species, the Ovenbird Seiurus aurocapilla Linnaeus and (ii) the age‐specific recruitment rate. Study plots ( n  = 10) were paired: one was treated through single‐tree selection harvesting (30–40% basal area removal) and the other acted as a control. We hypothesized that experienced males would out‐compete inexperienced ones and tend to avoid settling in lower‐quality, treated stands. 3.  In the first year post‐harvest, the mean density of territorial males was significantly lower in treated plots (−41%) than in controls and the difference remained relatively stable thereafter. This lower density mainly reflected a lower recruitment rate compared to controls (17·9 vs. 49·0% of males present), itself driven by a lower recruitment rate of experienced males (2·8 vs. 22·8%). Return rate was similar between controls and treated plots in the first year post‐harvest (59 vs. 55%, respectively) but it decreased in treated plots during the second (−15·8% relative to controls) and third (−12·7%) year post‐harvest. The trend was even stronger when considering only experienced males. The treatment was followed by a major expansion in mean territory size in treated plots (+49% relative to controls, 3rd year post‐treatment). 4 . Neither apparent survival rate nor recruitment rate varied as predicted. There was a strong year effect but no treatment effect on apparent survival rate, whereas male recruitment patterns were both year‐ and age‐specific. Three years post‐harvest, recruitment rate was sufficient to fill most territory vacancies in treated plots, due mainly to first‐time breeders. 5 . To our knowledge, this is the first study documenting the effects of experimental habitat alteration on recruitment rate in a songbird species using a BACI design. The response of this male subpopulation highlights the influence of recruitment on the density of open populations of solitary‐nesting birds and age‐specific patterns in the response of individuals to habitat alterations.