Leonard, Marty
Permanent URI for this collectionhttps://hdl.handle.net/10222/22306
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Item Open Access Characteristics of predators and offspring influence nest defense by Arctic and Common Terns(2000-05) Whittam, RM; Leonard, Marty L.Nest defense is a critical aspect of parental care that entails both costs and benefits. The purpose of this study was to examine patterns of nest defense in a colony of Arctic and Common Terns (Sterna paradisaea and S, hirundo, respectively) using observations of natural predators: Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L. marinus). Tern nest-defense scores were higher for hunting gulls than for overflying gulls and for gull flights closer to the ground. Defense scores also were significantly higher during the chick stage than during the egg stage. Within the chick stage. response score initially increased with age, but then declined. The results of this study indicate that terns vary their defense in relation to characteristics of predators and offspring that influence the costs and benefits of defense.Item Open Access Aggressive nest intrusions by male Humboldt Penguins(2001-02) Taylor, Sabrina S.; Leonard, Marty L.; Boness, Daryl J.During observations at a breeding colony of Humboldt Penguins (Spheniscus humboldti), we noted five male penguins enter nests occupied by breeding pairs and engage in aggressive interactions with the resident adult. These nest intrusions resulted in egg loss or infanticide, and accounted for 11.1% of breeding failure in the colony. Two intruder males ultimately mated with respective resident females. This behavior had not been observed previously in Humboldt Penguins and we suggest that it may occur when males are unable to obtain mates through advertising at the nest. Intrusion behavior may slow down population recovery in this endangered species.Item Open Access Mitochondrial DNA variation, species limits, and rapid evolution of plumage coloration and size in the Savannah Sparrow(2005-02) Zink, RM; Rising, JD; Mockford, S.; Horn, AG; Wright, JM; Leonard, Marty L.; Westberg, MCWe compared sequences from two mitochondrial DNA (mtDNA) genes (ND2, ND3) in Savannah Sparrows (Passerculus sandwichensis; n = 112) sampled from Baja California (five sites), coastal Sonora and the continental range (eight sites). Populations from Baja California, San Diego and Sonora formed a clade within which there was no phylogeographic structure; this clade merits species status (Passerculus rostratus). The other clade, consisting of phenotypically "typical" savannah sparrows, should be classified as P. sandwichensis. Among the typical sparrows, there was no phylogeographic structure, although two major clades were discovered. Representatives of each of the two main clades occurred at most sampling localities, excluding Suisan Bay, California and Sable Island, Nova Scotia, Canada. Haplotypes found on Sable Island, representing the "Ipswich Sparrow," were not distinctive, thereby failing to support species status for this taxon. On Isla San Benito, a single haplotype was found, which also occurred in other Mexican localities. The results for Sable Island and Isla San Benito show that size and plumage coloration can evolve rapidly.Item Open Access Seasonal and Age-Dependent Dietary Partitioning between the Great Black-Backed and Herring Gulls(2011-11) Steenweg, Rolanda J.; Ronconi, Robert A.; Leonard, Marty L.Studies of seabird diets may reveal subtle ways in which sympatric species partition resources to facilitate co-existence. We studied the variability and partitioning of diets between the Herring (Larus argentatus) and Great Black-backed Gulls (L. marinus), both generalist predators, during incubation and early chick rearing on Kent Island, Bay of Fundy, Canada. We assessed diets from pellets collected around nests, regurgitates from captured birds, and stable-isotope analysis of prey items and tissues (blood and feathers) obtained from chicks and adults. Pellet analyses indicated that both species relied primarily on fish (28 to 45% of identified prey items) and crabs (15 to 43%). Stable-isotope analyses showed that the Great Black-backed Gull fed at a higher trophic level than the Herring Gull, both species fed at higher trophic levels during breeding than during nonbreeding, and both species has similar preferences for feeding inshore vs. offshore and in terrestrial vs. marine habitats. Contrary to previous research, we found that chicks were fed from a lower trophic level than where adults feed. Models of isotopic mixing estimating the proportion of assimilated diets were generally consistent with the pellet analysis for adults but revealed that both species fed their chicks more krill (>60%; Meganyctiphanes norvegica) and mackerel (>20%; Scomber scombrus) than adults consumed; adults may selectively provision their young with easily digestible prey and prey of high energy content. Our results reveal evidence of dietary partitioning between species and age classes, and highlight the strengths and biases associated with techniques for sampling gulls' diet.Item Open Access Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America(2012-06) Shutler, Dave; Hussell, David J. T.; Norris, D. R.; Winkler, David W.; Robertson, Raleigh J.; Bonier, Frances; Rendell, Wallace B.; Belisle, Marc; Clark, Robert G.; Dawson, Russell D.; Wheelwright, Nathaniel T.; Lombardo, Michael P.; Thorpe, Patrick A.; Truan, Melanie A.; Walsh, Robert; Leonard, Marty L.; Horn, Andrew G.; Vleck, Carol M.; Vleck, David; Rose, Alexandra P.; Whittingham, Linda A.; Dunn, Peter O.; Hobson, Keith A.; Stanback, Mark T.Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78 degrees W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78 degrees W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broad-scale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America.Item Open Access The role of development, parental behavior, and nestmate competition in fledging of nestling Tree Swallows(2000-10) Michaud, T.; Leonard, Marty L.Fledging (i.e. leaving the nest) in altricial birds is a major step toward independence. The timing of this important event may be influenced by nestling development, parental behavior, and sibling interactions. In this study we examine the effect of these factors on fledging in Tree Swallows (Tachycineta bicolor). Wing length explained a significant proportion of the variance in fledging age across broods. Similarly, within broods, longer-winged nestlings fledged before shorter-winged nestlings. Feeding rate per nestling did not decrease in the period leading up to fledging, as might be expected if parents stimulated fledging by decreasing their feeding rate. Parental activity near the nest varied in that the frequency of parental passes and hovers within 1 m of the nest opening increased in the period before fledging. Brood size also explained a significant proportion of the variance in fledging age independent of wing length, although the direction of the relationship was not consistent across years. Finally, longer-winged nestlings spent more time in the nest opening and initiated fledging of the brood more often than did shorter-winged nestlings. Overall, our study suggests that nestling development is the most important determinant of fledging age in this species. Once a critical wing length has been reached, sibling interactions, and possibly parental behavior, may influence the timing of fledging.Item Open Access An experimental test of offspring recognition in Western Bluebirds(1995-10) Leonard, Marty L.; Dickinson, JL; Horn, AG; Koenig, W.No abstract available.Item Open Access Sex-specific, seasonal foraging tactics of adult grey seals (Halichoerus grypus) revealed by state-space analysis(2009-11) Breed, Greg A.; Jonsen, Ian D.; Myers, Ransom A.; Bowen, W. Don; Leonard, Marty L.In many large pelagic animals, observing behavior is limited to observation by radio or satellite telemetry. In many cases, discriminating different behaviors from telemetry data has been a key, but often elusive, goal. Here we use state-space models (SSMs) to fit a correlated random walk (CRW) model that switches between two unobserved behavioral states (nominally foraging and traveling) to 41 male and 43 female adult grey seal (Halichoerus grypus) satellite telemetry tracks. The SSM results reveal markedly different spatial behavior between the sexes, fitting well with sexual size dimorphism and known dietary differences, suggesting that the sexes deal with seasonal prey availability and reproductive costs differently. From these results we were also able to produce behaviorally informed habitat use maps, showing a complex and dynamic network of small, intensely used foraging areas. Our flexible SSM approach clearly demonstrates sex-related behavioral differences,. ne scale spatial and temporal foraging patterns, and a clearer picture of grey seal ecology and role in the Scotian Shelf ecosystem.Item Open Access Observer Effects and Avian-Call-Count Survey Quality: Rare-Species Biases and Overconfidence(2012-01) Farmer, Robert G.; Leonard, Marty L.; Horn, Andrew G.Wildlife monitoring surveys are prone to nondetection errors and false positives. To determine factors that affect the incidence of these errors, we built an Internet-based survey that simulated avian point counts, and measured error rates among volunteer observers. Using similar-sounding vocalizations from paired rare and common bird species, we measured the effects of species rarity and observer skill, and the influence of a reward system that explicitly encouraged the detection of rare species. Higher self-reported skill levels and common species independently predicted fewer nondetections (probability range: 0.11 [experts, common species] to 0.54 [moderates, rare species]). Overall proportions of detections that were false positives increased significantly as skill level declined (range: 0.06 [experts, common species] to 0.22 [moderates, rare species]). Moderately skilled observers were significantly more likely to report false-positive records of common species than of rare species, whereas experts were significantly more likely to report false-positives of rare species than of common species. The reward for correctly detecting rare species did not significantly affect these patterns. Because false positives can also result from observers overestimating their own abilities ("overconfidence"), we lastly tested whether observers' beliefs that they had recorded error-free data ("confidence") tended to be incorrect ("overconfident"), and whether this pattern varied with skill. Observer confidence increased significantly with observer skill, whereas overconfidence was uniformly high (overall mean proportion = 0.73). Our results emphasize the value of controlling for observer skill in data collection and modeling and do not support the use of opinion-based (i.e., subjective) indications of observer confidence. Received 13 June 2011, accepted 14 December 2011.