Experimental evidence that social information affects habitat selection in Marbled Murrelets

Habitat selection decisions can impact individual fitness and ultimately
scale up to mediate population dynamics. Understanding how birds select
habitat is thus critical for discerning the biological processes
structuring populations and developing conservation strategies,
particularly for species in decline. Marbled Murrelet (Brachyramphus
marmoratus; hereafter murrelet) populations have declined in recent
decades due to loss of late-successional forest nesting habitat and
changing ocean conditions that impact foraging success. Most other
seabirds in the family Alcidae nest colonially and evidence suggests
nesting murrelets may aggregate in stands, yet no studies have examined
murrelet use of social information in nest site selection. In 2016 we
experimentally simulated presence of murrelets at 14 randomly chosen
potential breeding sites by broadcasting murrelet calls throughout the
breeding period. Between broadcasting bouts, we recorded calls of wild
murrelets and compared call rates with those recorded at 14 control sites
(no broadcast). One year after playbacks ceased (2017) we conducted
breeding season surveys to document behaviors indicative of murrelet
breeding activity. Broadcasting murrelet calls in 2016 increased daily
odds of wild murrelets vocalizing during the treatment period by up to
15.4× (95% CI = 2.3, 125.4) relative to control sites. During the 2017
breeding season, the odds of occupancy were 10.0× (CI = 1.2, 81.4) greater
at treatment sites than control sites. These results indicate that social
information influences murrelet breeding site selection because simulated
conspecific presence in potential nesting habitat appeared to attract
prospectors in 2016 that continued occupying treatment sites the following
year. This conspecific attraction implies murrelet nesting sites are
likely to remain occupied over time and that large tracts of nesting
habitat may be important for supporting murrelet populations. Murrelets
may also be susceptible to information-mediated Allee effects whereby a
lack of conspecific information about nesting habitat could exacerbate
long-term population declines.