Reproductive Success and Evaluation of Management Strategies for Least Terns in Maine

Least Terns (Sterna antillarum) are state-listed as endangered in Maine, and the limited existing information indicates that breeding success is low and variable. Loss of nests and chicks to predators is believed to be a major cause of low productivity, and agencies are considering predator deterrence options. The objectives of this study were to document reproductive success of Least Terns in Maine and use these data to evaluate the effectiveness of management strategies. I also documented nocturnal nest attentiveness and examined relationships with nest depredation.. Least tern colonies in Maine were monitored to document clutch size, hatchability, nest success, chick survival and fledgling residency in 2002-2003. I used these data, excluding fledgling residency, to estimate increases in fledgling production for three levels of effectiveness at reducing nest and chick losses (30, 60, and 90%). Effectiveness levels were evaluated for five temporal management periods (intense nesting period, early season nesting, peak season nesting, late season nesting, and total season nesting). Nocturnal nest attentiveness was measured at three colonies during the nocturnal period (21:00-04:30) in 2002 and 2003. Hatchability was high (0.89-1.00) and clutch size (1.67-2.33) and nest success (0.00- 0.82) varied widely among colonies. Chick survival ranged from 0.15-0.74 among three breeding sites and mean SE fledgling residency for all sites and years pooled was 13.3 ± 0.7 days. The greatest increase in reproductive success occurred when management was applied for the entire nesting season (29 May-27 August), but early (29 May-16 July) and peak (12 June-30 July) nesting periods had similar and only slightly lower effectiveness. Management effectiveness ≥ 30% produced an increase in fledgling production above 1.0 for the total, early, and peak season periods. We monitored 119 nests for a total of 723 nocturnal periods and 5424 hr for nest attentiveness. The proportion of nest-nights with ≥ 1 absence ranged widely (0.07-0.63) and differed among colonies (P \u3c 0.001). The number of absences per nest-night for nests with absences differed among colonies and ranged from 1.0-1.4 (P \u3c 0.001). Overall, mean (±SE) absence length was 113 min (±8.86) but exhibited two distinct patterns. Incubation resumed either at dawn or within 1.5 hr after departure, regardless of departure time. Concurrent departures by ≥ 2 terns occurred commonly (generally more than 10% of nights monitored), but there was not evidence of simultaneous absences of all terns monitored in a colony being common. Mean absence length and proportion of nights with an absence did not differ (P \u3e 0.05) among the first, second, and third weeks of incubation. In conclusion, this reproductive success model showed that decreasing Least Tern nest and chick losses early or throughout the entire breeding season in Maine was adequate to sustain or increase Least Tern reproductive success to the putative level for population maintenance. In addition, nocturnal absences by Least Terns in Maine are common and often of long duration, but nest attentiveness did not exhibit relationships with nest depredation in colonies. Additional research is needed on the cause and consequences of poor nest attentiveness of Least Terns in Maine