Premium
THE SURVIVAL VALUE OF FLOCKING IN NEOTROPICAL BIRDS: REALITY OR FICTION?
Author(s) -
Jullien Mathilde,
Clobert Jean
Publication year - 2000
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2000)081[3416:tsvofi]2.0.co;2
Subject(s) - obligate , facultative , flock , biology , ecology , survivorship curve , fecundity , foraging , flocking (texture) , zoology , avian clutch size , life history theory , animal ecology , demography , reproduction , life history , population , genetics , materials science , cancer , sociology , composite material
Greater foraging efficiency and/or better predator avoidance have long been assumed and used as explanations for the evolution of flocking behavior in birds. Even if the debate between the validity of these two hypotheses remains open, one prediction is that living in flocks can favor increased survival rates. We gathered published and unpublished data from various tropical forests where bird species forage (1) exclusively alone or in pairs (2) in heterospecific flocks some of the time (facultative flock members), or (3) exclusively in heterospecific year‐long associations (obligate flock members). We controlled statistically for effects of body size, nest type, clutch size, and phylogeny, and tested whether survival rates differed among these three groups. The survival rates of the obligate flock members (mean survival rate 68.7%, range 48.0–87.0%) were significantly higher than estimates for the species feeding alone or in pairs (mean survival rate 58.3%, range 33.0–79.0%). However, survival rates of the facultative flock members (mean survival rate 60.4%, range 40.0–79.0%) did not differ from those of the nonflocking species. Nevertheless, causes of such differences in survival can be explained by an alternative hypothesis. Life history theory predicts that higher survival for the obligate flocking species may be a response to low fecundity and productivity. Yet, the pattern “high survivorship, strikingly low fecundity” documented in obligate flocking species has never been observed among their solitary or facultative flocking counterparts. This result suggests that permanent obligate flocking can be an alternative ecological factor that may drive the evolution of life histories in tropical birds.