The difficulties in understanding the underlying reasons of a population decline lie in the typical short duration of field studies, the often too small size already reached by a declining population or the multitude of environmental factors that may influence population trend. In this difficult context, useful demographic tools such as integrated population models (IPM) may help disentangling the main reasons for a population decline.

To understand why a hoopoe Upupa epops population has declined, we followed a three step model analysis. We built an IPM structured with respect to habitat quality (approximated by the expected availability of molecrickets, the main prey in our population) and estimated the contributions of habitat-specific demographic rates to population variation and decline. We quantified how much each demographic rate has decreased and investigated if habitat quality influenced this decline. We tested how much weather conditions and research activities contributed to the decrease of the different demographic rates.

The decline of the hoopoe population was mainly explained by a decrease in first-year apparent survival and a reduced number of fledglings produced, particularly in habitats of high quality. Since a majority of pairs bred in habitats of the highest quality, the decrease of the production of locally recruited yearlings in high-quality habitat was the main driver of the population decline despite a homogeneous drop of recruitment across habitats.

Overall, the explanatory variables we tested only accounted for 19% of the decrease of the population growth rate. Among these variables, the effects of spring temperature (49% of the explained variance) contributed more to population decline than spring precipitation (36%) and research activities (maternal capture delay, 15%). This study shows the power of IPMs for identifying the vital rates involved in population decline, and thus pave the way for targeted conservation and management actions.

Repro_data2.txt: One line is the reproduction data of one hoopoe female in a given year. For each female, the year, the habitat quality of the nestbox, the hatching date of the first brood, the total clutch size, the probability of having at least one fledgling and the number of fledglings are given.

Surv_and_pop_data.Rdata:

-BP: count data: Number of breeding pairs per year (line) and per habitat quality type (column).

-CH: Survival data: Individual capture histories: lines are individuals and columns are years. There are 4 events: 1,2,3: Captured in a Nestbox of habitat quality 1, 2 and 3; 4: Not captured.