Influences of a periodical cicada emergence on eastern phoebe reproduction and behavior

Allison M Klement, Purdue University

Abstract

I examined southern Indiana Eastern Phoebe (Sayornis phoebe) reproductive responses to the emergence of Brood X of the 17-year periodical cicada (Magicada septendecim, M. cassini, and M. septendcula) in 2004 (cicada year) and compared results with a period of more typical food abundance in 2005 (non-cicada year). A periodical cicada emergence produces a superabundant pulse of protein-rich, highly palatable prey with limited predator avoidance tactics. Typically double-brooded, phoebes often lay smaller late-season clutches about 2-weeks after the fledging of early-season broods. The unlimited prey base was available during the early-season nestling and fledgling phases, and throughout late-season egg laying, incubation, and brood rearing in 2004. During the cicada emergence, phoebes more rapidly initiated late-season clutches (intra-clutch interval: 44 ± 2 days vs. 50 ± 4 days; p < 0.0001). Late-season clutches in the cicada year were larger than typical (4.85 eggs vs. 4.45; p < 0.0001), and resulted in more young fledging than in the non-cicada year (3.66 fledglings vs. 3.14; p = 0.0291). Early-season fledglings, fitted with radio-transmitters, were less often located with their siblings (68% vs. 92% of observations; p = 0.0042), and tending parents (32% vs. 87%; p = 0.0002) during the cicada emergence, both indications of increased fledgling independence while food was superabundant. Additionally, fledgling movement was reduced in the cicada year; family groups tended to remain closer to the nest site than in the non-cicada year. Late-season incubation patterns in the cicada year shifted toward a more optimal strategy; females spent a greater proportion of the day incubating (73% vs. 64% attentiveness; p < 0.0001) while reducing movement to and from the nest (3.3 vs. 4.6 recesses per hr; p = 0.0015). The increased incubation attentiveness resulted in the reduction of the incubation period by about 1 day (p = 0.0001). Parents must allocate resources between reproductive events and self-maintenance. During the cicada emergence, females may have better maintained endogenous reserves, allowing for more rapid late-season clutch initiation because less time was required to secure sufficient nutrients and energetic reserves for egg production. Increased fledgling independence would also allow more time for parents to engage in self-maintenance foraging, additionally increasing opportunity for more rapid late-season clutch initiation. Results of this study suggest that phoebes are food limited during reproduction, the timing and number of young produced in the late-season reflect energetic costs incurred during early-season reproductive events. When food is superabundant, ameliorating energetic costs, reproductive strategies may be optimized to allow increased fecundity and reduced predator exposure days of the nest.

Degree

M.S.

Advisors

Weeks, Purdue University.

Subject Area

Ecology

COinS