Daniel H. Catlin

Range-Wide Piping Plover Survival: Correlated Patterns and Temporal Declines

Abstract Geographically isolated breeding populations of migratory shorebirds may be demographically connected through shared nonbreeding habitats. We used long-term (1998–2008) mark–recapture data on piping plovers (Charadrius melodus) collected from 7 separate studies located throughout North America to conduct a range-wide analysis of after hatch year apparent survival (ΦAHY). Our objectives were to compare concurrent survival estimates from disparate breeding sites and determine whether estimates followed similar trends or were correlated among breeding populations with shared wintering grounds. Average survival estimates were higher for Great Plains populations (range  =  0.69–0.81) than for Great Lakes and Atlantic Coast populations (range  =  0.56–0.71). Linear trend models indicated that apparent survival declined in 4 out of 7 populations, was unchanged in 3, and was generally highest among Great Plains populations. Based on a post hoc analysis, we found evidence of correlated year-to-year fluctuations in annual survival among populations wintering primarily along the southeastern United States Atlantic Coast and Gulf Coast. Our results indicate shared overwintering or stopover sites may influence annual variation in survival among geographically disparate breeding populations. Declines in piping plover survival are a cause for concern, and our results highlight the need for conservation efforts to include habitat used during the migratory and wintering periods.

Effect of Great-Horned Owl Trapping on Chick Survival in Piping Plovers

ABSTRACT We studied the effect of great-horned owl (Bubo virginianus) removal on piping plover (Charadrius melodus) hatchling survival on Missouri River sandbars (2008–2009). Owl removal increased daily survival of piping plover chicks in 2008 (&bgr; = 2.03, 95% CI: 0.04–4.02), but this effect decreased with increasing age of the chick (&bgr; = -0.42, 95% CI: -0.81 to -0.03). Results for 2009 were similar in direction but not significant. Survival was higher in 2008 than in 2009, regardless of owl capture, indicating that even if owl capture consistently were effective at increasing survival, overall survival resulting from trapping may vary annually. Owl trapping was a successful means to raise chick survival on the Missouri River in ≥1 year and could be used at other sites experiencing depressed chick survival due to avian predators.

Winter Ecology of Piping Plovers at Oregon Inlet, North Carolina

Abstract Humans may modify winter habitat of the imperiled Piping Plover (Charadrius melodus), yet published accounts of the species’ winter ecology are rare. We studied Piping Plovers at Oregon Inlet, North Carolina from December 2005 to March 2006. Plovers used a 20.1 km2 area (100% minimum convex polygon home range) containing narrow barrier islands with ocean and sound-side beaches, and small shoals, dredged-material islands, and marsh islands in shallow-water sounds. Plover activity was concentrated in twelve areas totaling 2.2 km2 (95% fixed kernel home range). When plovers were on ocean beaches, they spent less time foraging (18%) than when on Sound Island beaches (88%) and islands (83%, P = 0.003). Sound island use increased and beach use decreased as the tide dropped (Logistic regression, P < 0.001). Plover use of dredged-material islands implied that habitat managers can create or restore attractive foraging sites where habitat may be declining or limiting. Wintering habitat management should aim to provide foraging opportunities during most of the day and across a range of tide conditions and ensure that foraging habitat is close to roost sites.

Breeding Dispersal and Nesting Behavior of Burrowing Owls Following Experimental Nest Predation

ABSTRACT Nest predation is considered a primary factor affecting the life-history characteristics and particularly dispersal of many avian species. We tested the hypothesis that nest predation would increase dispersal probability, dispersal distance and the frequency of renesting. We removed eggs from burrowing owl (Athene cunicularia) nests to simulate nest predation in southeastern California. Owls responded to egg removal with increased dispersal probability, nesting attempts and egg production. We found that nest predation tended to increase dispersal probability (50% depredated nests vs. 14% control nests), which occurred fairly soon after nest predation (0–25 d). Dispersal distance was highly variable among owls (range: 148–13,012 m). Following experimental nest predation, burrowing owls increased the number of nesting attempts and thus the total number of eggs produced in a season, regardless of dispersal. Clutch size, however, decreased as the number of breeding attempts increased. Despite large initial clutch size, burrowing owls in the Imperial Valley may have adapted to nest predation by both dispersal and the ability to renest frequently.

Body Condition Indices Predict Reproductive Success but Not Survival in a Sedentary, Tropical Bird

Body condition may predict individual fitness because those in better condition have more resources to allocate towards improving their fitness. However, the hypothesis that condition indices are meaningful proxies for fitness has been questioned. Here, we ask if intraspecific variation in condition indices predicts annual reproductive success and survival. We monitored a population of Neochmia phaeton (crimson finch), a sedentary, tropical passerine, for reproductive success and survival over four breeding seasons, and sampled them for commonly used condition indices: mass adjusted for body size, muscle and fat scores, packed cell volume, hemoglobin concentration, total plasma protein, and heterophil to lymphocyte ratio. Our study population is well suited for this research because individuals forage in common areas and do not hold territories such that variation in condition between individuals is not confounded by differences in habitat quality. Furthermore, we controlled for factors that are known to impact condition indices in our study population (e.g., breeding stage) such that we assessed individual condition relative to others in the same context. Condition indices that reflect energy reserves predicted both the probability of an individual fledging young and the number of young produced that survived to independence, but only during some years. Those that were relatively heavy for their body size produced about three times more independent young compared to light individuals. That energy reserves are a meaningful predictor of reproductive success in a sedentary passerine supports the idea that energy reserves are at least sometimes predictors of fitness. However, hematological indices failed to predict reproductive success and none of the indices predicted survival. Therefore, some but not all condition indices may be informative, but because we found that most indices did not predict any component of fitness, we question the ubiquitous interpretation of condition indices as surrogates for individual quality and fitness.

Diurnal Time Budget of Burrowing Owls in a Resident Population During the Non-Breeding Season

Abstract We present the first non-breeding-season time budget of adult burrowing owls (Athene cunicularia). We evaluated the hypothesis that during the non-breeding season the gender-specific allocation of time and effort observed diurnally in the breeding season changes, with males and females exhibiting more similar time budgets. Owls spent most of their time alert (58.4 ± 7.2% and 42.6 ± 8.3%) and in the burrow (19.3 ± 5.3% and 46.2 ± 7.2% for males and females, respectively). Females tended to spend more time in the burrow, and males spent more time alert. Although we found little evidence for temporal variation of these patterns for males, females were found more often in the burrow during early afternoon. Our results support a hypothesis that time-allocation differences between males and females during the breeding season are at least partially retained into the non-breeding season. The major finding of the study was the high percentage of time owls spent within the nest burrow during the non-breeding season, contrary to previous understanding of the ecology of this species from which management guidelines are based. Our findings indicate that considerable care should be taken when modifying areas that contain burrows within areas occupied by burrowing owls during the non-breeding season.

The importance of site to mate choice: Mate and site fidelity in Piping Plovers

ABSTRACT Each breeding season, seasonally monogamous birds can divorce or reunite with their previous years mate, assuming both partners survive and return. We tested a suite of variables related to mate choice and site choice to determine which of 4 prominent mate fidelity hypotheses (better [mate] option, habitat mediated, musical chairs, and bet-hedging) best explained the interyear reunion rate and breeding dispersal of a seasonally monogamous shorebird, Piping Plover (Charadrius melodus), nesting on dynamic sandbars on the Missouri River, USA, 2005–2012. Of 252 pairs in which both members returned to the breeding grounds the following year, only 20% reunited. Pairs with an early-arriving male had the highest mate fidelity. Reunited pairs returned to previous nest sites (median breeding dispersal = 39 m), and divorced and widowed birds tended to move farther (median = 229 m and 193 m, respectively). Overall, site fidelity was higher in males than females. Previous reproductive success of a pair did not predict reunion, but all successful birds, with the exception of divorced females, exhibited high site fidelity, suggesting selection for site based on prior breeding success. Among divorced birds, females had higher-quality mates and higher nest success compared to their former partners, and they nested in areas of similar quality between years, whereas males settled in lower-quality areas following divorce. The benefits that females gained from divorce suggested that females initiated divorce to improve reproductive success, which supports the better option hypothesis. Although females seemed to initiate most divorces, males may have divorced as a safeguard against remaining unmated when there was uncertainty about the survival and return of a former mate, as proposed by the bet-hedging hypothesis.

ENVIRONMENTAL CORRELATES OF BREEDING IN THE CRESTED CARACARA (CARACARA CHERIWAY)

ABSTRACT. We evaluated the influence of weather on reproduction of the Crested Caracara (Caracara cheriway) in an agricultural landscape in south-central Florida. We used a mixed logistic-regression modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the number of breeding pairs, timing of breeding, nest success, and productivity of Crested Caracaras during 1994–2000. The best models indicated an influence of rainfall frequency and laying period on reproduction. More individuals nested and more pairs nested earlier during years with more frequent rainfall in late summer and early fall. Pairs that nested later in each breeding season had smaller clutches, lower nest success and productivity, and higher probability of nest failure. More frequent rainfall during early spring months that are usually characterized by water deficit (March–May), more frequent rainfall during the fall drawdown period (September–November), and a shorter winter dry period showed some association with higher probability of brood reduction and lower nest success. The proportion of nests that failed was higher in “wet” years, when total rainfall during the breeding season (September–April) was >10% above the 20-year average. Rainfall may influence reproduction in Crested Caracaras indirectly through food resources. As total rainfall increased during February–April, when most pairs are feeding nestlings or dependent fledglings, the proportion of drawdown-dependent species (those that become available as rainfall decreases and wetlands become isolated and shallow) in the diet of Crested Caracaras declined, which may indicate reduced availability of foraging habitat for this primarily terrestrial raptor.

ENVIRONMENTAL CORRELATES OF NESTING SUCCESS IN RED-SHOULDERED HAWKS

Abstract Abstract. We evaluated the influence of weather on reproduction of the Red-shouldered Hawk (Buteo lineatus) in an agricultural landscape in south-central Florida where we found relatively high densities of successfully nesting hawks. We used a generalized linear modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the timing of nesting, nesting success, and productivity of hawks during 1995–2000. The best models indicated an influence of rainfall frequency and laying period on hawk reproduction. During years with less frequent rainfall in the summer and fall months prior to the beginning of the breeding season, fewer pairs attempted to nest, and hawks nested later and had smaller clutch sizes and lower productivity. Hawks that nested later in the breeding season had lower hatching success and lower overall nest success. Although Red-shouldered Hawks are generally reported to inhabit forested landscapes throughout their range, a common feature seems to be a dependence on wetlands and riparian habitat for foraging. We propose that the proportion of wetlands throughout the landscape is a unique aspect of south-central Florida that may allow for persistence of unusually high numbers of hawks.

Density Dependent Double Brooding in Piping Plovers (Charadrius melodus) in the Northern Great Plains, USA

Abstract. Piping Plovers (Charadrius melodus) are primarily monogamous birds that usually raise only one brood per season, but rare instances of double brooding have been documented. Piping Plovers breeding in the northern Great Plains, USA were studied in two locations: the Missouri River near the Gavins Point Dam (2005– 2013) and the lower Platte River (2008–2013). There were 25 confirmed instances of double brooding on the Missouri River across the 9-year duration of the study. There were no instances of double brooding observed locally on the lower Platte River. However, in 2013, two female Piping Plovers successfully hatched eggs and fledged chicks from nests on the lower Platte River and later were observed nesting for a second time on the Missouri River. Factors predicted to increase the frequency of double brooding are: early nest initiation, male biased sex ratio, age of breeding adults, and decreased nesting density. Our results indicate density is an important factor that accounts for some of the difference in the proportion of double brooding on the Missouri River compared to the lower Platte River. It is likely a combination of factors is responsible for this behavior, previously thought to be rare, in Piping Plovers.