Habitat variables influencing bird assemblage patterns across maize and legume fields before and after harvest in West Africa

Though agriculture has been linked to the decline in bird populations due
to the associated changes in vegetation structure and composition, its
potential to sustain birds has been explored over time. A sustainable
agricultural landscape should be one that has the capacity to support bird
species all year. To this end, we investigated the factors influencing
pre- and post-harvest farm conditions on bird abundance, richness, and
feeding guilds in three different crop fields in Jos-East and North,
central Nigeria. We used line transects to survey birds and vegetation
variables from 30 fields each of legumes, maize, and mixed (maize and soya
bean) during the pre- and post-harvest periods in central Nigeria. We
modeled the effects of field conditions and vegetation parameters on bird
species richness and encounter rates at overall and feeding-guild levels.
Our results showed that bird species richness was significantly higher
pre-harvest than post-harvest. Bird encounter rate and feeding guild
encounter rate were not affected by pre- and post-harvest conditions. Bird
species richness, encounter rate, and guild encounter rate were
significantly higher in legume and mixed crop fields than in maize fields.
In addition, in-field tree density had a significant positive influence on
bird and guild encounter rates, and species richness. Bird encounter rate
and richness were significantly higher when the nearest noncrop vegetation
was either a gallery forest or rocky outcrop. A similar trend was observed
for both insectivore and granivore encounter rates. Bird encounter rate
declined with increasing distance from water sources and noncrop
vegetation. This study shows that pre- and post-harvest conditions of crop
fields can moderate the number and richness of birds on farmlands while
the retention of trees on farmlands contributes to higher bird
assemblages.