Waterbird Communities and Habitat Relationships in Coastal Pastures of Northern California

We examined waterbird assemblages (diversity, composition, and species' densities) in 20 pastures near Humboldt Bay, California, in relation to habitat characteristics (vegetation height, soil penetrability, water depth), abundance of invertebrates (worms and other invertebrates), and presence of livestock. From October 1991 to May 1992 we observed 29 species and 10,776 birds, most (78%) of which foraged. Nonrandom pasture use by birds resulted in a highly clumped spatial distribution (s²:{ovbar>x} ratio = 42.1). Habitat characteristics of pastures correlated with this nonrandom pattern: waterbird diversity and densities of three sandpiper species and one gull species correlated negatively ( r = −0.61 and r = −0.44 to −0.67, respectively) with vegetation height; densities of two plover species correlated negatively ( r = −0.39 and −0.45) with soil penetrability; and waterfowl densities correlated positively with water depth ( r = 0.97). Species composition varied among pastures. Wading birds used pastures with tall vegetation, shorebirds and gulls frequented short-grass pastures, and waterfowl used flooded pastures of waterbirds and their densities increased in association with livestock.In coastal areas where much intertidal habitat has been reclaimed as postureland, pastures offered valuable habitats to nonbreeding waterbirds. We suggest that grazing in coastal pastures can be used to provide a mosaic of vegetation heights, which would yield greater waterbird diversity as well as higher densities of some species.     

Female mate choice in the zebra finch — the effect of male beak colour and male song

Studies of female mate preference in zebra finches (Taenopygia guttata) have shown that male beak colour and song rate are important. However, the two characters are correlated. Here the effect of beak colour and song rate on female choice are examined independently. In mate choice tests involving two males, beak colour was manipulated artificially using nail varnish. The results showed that females showed a significant preference for males with a high song rate, but not with a red beak. Females did not prefer males with a red beak if song rate was low and females preferred males with orange beaks who expressed a high song rate. Female preference for males with red beaks was not found when beak and song characters were no longer correlated.     

Wintering areas of adult Atlantic puffins Fratercula arctica from a North Sea colony as revealed by geolocation technology

Most seabirds die outside the breeding season, but understanding the key factors involved is hampered by limited knowledge of nonbreeding distributions. We used miniature geolocating loggers to examine the movements between breeding seasons of Atlantic puffins Fratercula arctica from a major North Sea colony where numbers have declined in recent years, apparently due to increased overwinter mortality. The most intensively used region was the northwestern North Sea but most puffins also made excursions into the east Atlantic in the early winter. Ringing recoveries previously indicated that adults from British east coast colonies remained within the North Sea and hence were spatially segregated from those breeding on the west throughout the year. Updated analyses of ringing recoveries support results from geolocators suggesting that usage of Atlantic waters is a recent phenomenon. We propose that the increased adult mortality is related to changes in distribution during the nonbreeding period and reflects worsening conditions in the North Sea.     

Carotenoid-based status signalling in red-shouldered widowbirds (<Emphasis Type="Italic">Euplectes axillaris</Emphasis>): epaulet size and redness affect captive and territorial competition

In breeding plumage, the African male red-shouldered widowbirds (Euplectes axillaris) are black except for red carotenoid-based epaulets ('shoulder patches'), similar to the well-studied American red-winged blackbirds (Agelaius phoeniceus). To experimentally test the signal function of the red epaulets in male red-shouldered widowbirds, we manipulated epaulet colour and size (within natural variation), and observed the effects in two competitive contexts. First, in captivity, unfamiliar males with epaulets of different size or redness were staged in dyadic contests over food. Only epaulet manipulations significantly affected contest outcome; red epaulet males out-competed orange and control males, which in turn dominated blackened (no epaulet) males. Epaulet size manipulations had particularly strong effects; enlarged epaulet males vigorously defeated smaller epaulet males within colour treatments, whereas the independent effect of 'redness' (i.e., within size treatments) was much weaker. Second, in a field experiment, epaulets were manipulated prior to territory establishment. Males with enlarged epaulets acquired territories, whereas most males with blackened or reduced signals failed to obtain territories. Furthermore, among the territorial males, birds with enlarged epaulets defended larger territories and spent less time in boundary signalling, yet they received fewer intrusions from conspecifics. In contrast, epaulet manipulations had no effect on either female visitation rates or subsequent female settlement. These results concur with recent studies and suggest that the carotenoid-based epaulets of red-shouldered widowbirds are status signals, sexually selected through male contest competition for territories.     

Species' traits predict phenological responses to climate change in butterflies

How do species' traits help identify which species will respond most strongly to future climate change? We examine the relationship between species' traits and phenology in a well-established model system for climate change, the U.K. Butterfly Monitoring Scheme (UKBMS). Most resident U.K. butterfly species have significantly advanced their dates of first appearance during the past 30 years. We show that species with narrower larval diet breadth and more advanced overwintering stages have experienced relatively greater advances in their date of first appearance. In addition, species with smaller range sizes have experienced greater phenological advancement. Our results demonstrate that species' traits can be important predictors of responses to climate change, and they suggest that further investigation of the mechanisms by which these traits influence phenology may aid in understanding species' responses to current and future climate change.