Blue Jays Research Articles

RHODAMINE-INJECTED EGGS TO PHOTOGRAPHICALLY IDENTIFY SMALL NEST-PREDATORS

Photographs that clearly disclose avian-nest predators are difficult to obtain, particularly when predators are small and exhibit subtle depredatory behavior. We exposed House Sparrow (Passer domesticus) eggs injected with Rhodamine B dye in camera-monitored ground nests for 12-d periods at 76 sites within mixed-hardwood forest stands in central Massachusetts, June–July 1997. Dye-injected eggs enabled us to recognize with certainty when eggs were breached at the nest because their contents were fluorescent pink and readily detected photographically. Eleven potential predator species were identified disturbing nests, of which eight were confirmed as predators. Eastern chipmunks (Tamias striatus) were the most frequent predators detected, along with fisher (Martes pennanti), raccoon (Procyon lotor), Blue Jays (Cyanocitta cristata), Black-capped Chickadees (Poecile atricapillus), red squirrels (Tamiasciurus hudsonicus), an Eastern Towhee (Pipilo erythrophthalmus), and a white-footed mouse (Peromyscus leucopus). White-footed mice were the most commonly detected species disturbing nests, but were photographed only once actually destroying an egg. The visual cue provided by dye-injected House Sparrow eggs confirmed depredatory behavior by eastern chipmunks, Black-capped Chickadees, an Eastern Towhee, and a white-footed mouse.

The cost of limited attention in blue jays

Experiments with fish and birds suggest that animals are unable to simultaneously allocate sufficient attention to tasks such as the detection of an approaching predator while searching for cryptic prey. We quantified the effects of limited attention on performance in controlled laboratory settings and report here the first direct evidence that attending to a difficult central task simulating foraging deters a bird's ability to detect a peripheral target, which could be a predator. Our results fill a gap between ecological and neurobiological studies by illustrating that, although attention is an efficient filtering mechanism, limited attention may be a major cause of mortality in nature.

Recreational trails, human activity, and nest predation in lowland riparian areas

In areas of human settlement, greenways and open-space land are often intended to serve recreational purposes as well as provide wildlife habitat, but the compatibility of these goals is uncertain. We examined the effect of recreational trails on the risk of nest predation and nest predator activity at four lowland riparian sites along the Front Range of Colorado. At one site on each of two streams, we placed a transect of artificial nests near a recreational trail and another transect on the opposite side of the stream. We also placed another transect of nests at a second site on each stream that was not associated with a recreational trail. In 1995, nests were baited with quail eggs; in 1996 a clay egg was also added to nests to aid us in nest predator identification. Artificial nests are not perfect surrogates for natural nests, but are useful in generating hypotheses about causes of nest failure and for detecting changes in predator assemblages. Overall, predation rates were high (94%). There were significant differences in vulnerability to predation on the different transect types, with a tendency for predation rates to increase with distance from trails. There was a significant effect of time with a greater risk of predation in 1996. In 1996, 83% of the clay eggs that were recovered showed signs of predation. House Wrens destroyed 11% of the clay eggs; impressions from Black-billed Magpies, Blue Jays, and Common Grackles were found on 69%; mice preyed on 25%; and squirrels on 12% of the eggs. Birds attacked more nests near trails than away from trails, whereas mammals appeared to avoid nests near trails to some extent. These results support the contention that recreational trails and human activity may affect nesting success for some species, and suggest that patterns of nest predation reflect the unique, and sometimes, counter-intuitive responses of individual predator species. Rather than relying on simplistic assumptions about the compatibility of recreation and wildlife, it is important to consider how individual species respond to the habitat alteration and human activity associated with trails when deciding where trails should be located and in developing overall conservation strategies in human-dominated areas.

Dynamics and phylogenetic implications of MtDNA control region sequences in New World Jays (Aves: Corvidae).

To study the evolution of mtDNA and the intergeneric relationships of New World Jays (Aves: Corvidae), we sequenced the entire mitochondrial DNA control region (CR) from 21 species representing all genera of New World jays, an Old World jay, crows, and a magpie. Using maximum likelihood methods, we found that both the transition/transversion ratio (kappa) and among site rate variation (alpha) were higher in flanking domains I and II than in the conserved central domain and that the frequency of indels was highest in domain II. Estimates of kappa and alpha were much more influenced by the density of taxon sampling than by alternative optimal tree topologies. We implemented a successive approximation method incorporating these parameters into phylogenetic analysis. In addition we compared our study in detail to a previous study using cytochrome b and morphology to examine the effect of taxon sampling, evolutionary rates of genes, and combined data on tree resolution. We found that the particular weighting scheme used had no effect on tree topology and little effect on tree robustness. Taxon sampling had a significant effect on tree robustness but little effect on the topology of the best tree. The CR data set differed nonsignificantly from the tree derived from the cytochrome b/morphological data set primarily in the placement of the genus Gymnorhinus, which is near the base of the CR tree. However, contrary to conventional taxonomy, the CR data set suggested that blue and black jays (Cyanocorax sensu lato) might be paraphyletic and that the brown jay Psilorhinus (=Cyanocorax) morio is the sister group to magpie jays (Calocitta), a phylogenetic hypothesis that is likely as parsimonious with regard to nonmolecular characters as monophyly of Cyanocorax. The CR tree also suggests that the common ancestor of NWJs was likely a cooperative breeder. Consistent with recent systematic theory, our data suggest that DNA sequences with high substitution rates such as the CR may nonetheless be useful in reconstructing relatively deep phylogenetic nodes in avian groups.

Effectiveness of nest defence in the Acadian Flycatcher Empidonax virescens

We used presentations of models to determine the effectiveness of nest defence in the Acadian Flycatcher Empidonax virescens against a nest predator (Blue Jay Cyanocitta cristata) and a brood parasite (Brown‐headed Cowbird Molothrus ater). Principal components analysis (PCA) of four component variables of nest defence (call rate, swoop rate, closest approach and number of adults) generated a measure of overall nest defence (aggression). We determined effectiveness of defence by looking for correlations between measures of defence and measures of nest success (nest predation and brood parasitism). We also determined whether nest defence increased with clutch size, nestling age and time in the breeding season. Defence against model Brown‐headed Cowbirds did not correlate with levels of parasitism, clutch size, age of young or time of breeding. There was, however, a strong, but insignificant, trend for nests with high levels of all measures of defence to suffer less from brood parasitism. Aggression, vocalization rate, closest approach and number of adults defending against models of predatory Blue Jays correlated positively with nesting success during the egg stage but not the nestling stage of the nesting cycle. Aggression, vocalization rate, closest approach correlated with clutch size and age of the brood. These results suggest that nest defence can effectively deter nest predators, but may be less effective against brood parasites. Different behavioural components of nest defence may work at different stages of the nest cycle and against different nest predators. The components of nest defence that correlated with nest success also correlated with clutch value, a result consistent with hypotheses on the evolution of nest defence.

Toronto Meeting Highlights - Summer 2000

The fair city of Toronto welcomed attendees of the Society’s 197th meeting. Over 1,600 registrants were able to choose from 1,310 papers in 34 symposia. Visitors could take in a Blue Jays baseball game or any number of exhibits in the city’s impressive museums, as well as enjoy the abundant restaurants and tourist attractions. The favored occupation in the free hours of the meeting was comparing notes on how many moose had been spotted.

Housing developments in rural New England: effects on forest birds

AbstractIn rural New England, forest fragmentation is caused by housing developments in forested areas. To evaluate the effects of these changes on forest birds, we compared bird assemblages between forests with different housing densities in western Massachusetts. Species occurrences and relative abundances were determined from systematic point count surveys and mist‐netting at three plots in forest of low housing density (0–0.05 houses/ha) and of moderate housing density (0.60–6.70 houses/ha) in 1993 and 1994. Among guilds, Neotropical migrants and forest‐interior species had significantly lower abundances in forests of moderate housing density. Abundances of ground/shrub nesting birds as a group, and of individual species such as veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus) and wood thrush (Hylocichla mustelina), were greater in forest of low housing density, but blue jays (Cyanocitta cristata) were more abundant in forest of moderate housing density. Although the abundances of ground/shrub nesting birds were positively related to ground cover, this vegetation structure did not differ between forest types. Avian and mammalian nest predators may be responsible for the trends in bird abundance. Avian nest predators may recognize forest of moderate housing density as edge habitat, and this rural development may also support relatively high densities of mammalian nest predators. These trends suggest that birds of New England's relatively extensive forests may be subject to greater fragmentation effects than generally thought, as a result of increasing rural housing development within forests.

Searching image in blue jays: Facilitation and interference in sequential priming

Repeated exposure to a single target type (sequential priming) during visual search for multiple cryptic targets commonly improves performance on subsequent presentations of that target. It appears to be an attentional phenomenon, a component of the searching image effect. It has been argued, however, that if searching image is an attentional process, sequential priming should also interfere with performance on subsequent nonprimed targets, and such interference has never been unequivocally demonstrated. In blue jays (Cyanocitta cristata) searching in an operant apparatus for targets derived from images of cryptic moths, detection performance was strongly facilitated in the course of a sequential prime but was relatively unaffected by sequences of mixed target types. Detection accuracy in subsequent probe trials was enhanced by priming with targets of the same type, whereas accuracy on cryptic probes following priming with a more conspicuous target was significantly degraded. The results support an attentional interpretation of searching image.

Nest Predation on Woodland Songbirds: When Is Nest Predation Density Dependent?

Nest predation. if density dependent, may structure avian communities by selecting for nest-site characteristics that dilute the predators' perception of nest density (e.g., by increasing the number and types of potential nest sites) thereby reducing losses to predators. We tested for density dependent nest predation at a site dominated by predation from raccoons, Procyon lotor. and blue jays. Cyanocitta cristata. We used cohorts of 20 artificial ground nests placed on experimental grids at four densities (1.7, 7, 65, and 167 nests/ha). Predation was density dependent for one of two temporal replicates. In a second experiment, we tested for density dependent predation on both ground and shrub nests using more realistic nest densities (3.5 and 8.9 nests/ha) and excluding avian and small mammal predators by placing nylon screening over the nests. Predation was density dependent on artificial ground nests and density independent on shrub nests. Finally, we analyzed predation on natural shrub nests separating out avian (i.e., jays) and large mammalian predation based on disturbance to the depredated nest. In each of three years there was no evidence for density dependent predation. An outbreak of periodic cicadas in the first experiment and the maturation of a large mulberry crop during the second experiment demonstrated the importance of the distribution and abundance of alternative foods on the response of predators toward heterogeneity in nest abundance.

Addendum to Problems and Benefits of Bird Ownership

Because several recent studies suggested that adults who fed only wild birds would report having different problems and benefits than did pet bird owners who also fed wild birds, and pet bird only owners, the present study added data to clarify such differences. 150 adults were selected so that 50 persons (25 men and 25 women) each were classified into one of three groups: those who only owned pet birds, those who owned pet birds and also fed wild birds, and those who only fed wild birds. There were no significant differences between men and women in any of the three groups, and no significant differences in their responses. The 50 people who fed wild birds only reported having added problems with neighbors' cats, bees, ants, squirrels, blue jays, and other oppressive larger birds, but the 50 pet bird owners who also fed wild birds and the owners of pet birds only reported the same problems with minor differences in type and number of interlopers. Clearly, all bird lovers shared similar characteristics, feelings, and behaviors toward birds and acknowledged the minor differences in attitudes toward the benefits and problems created by the birds' various interactions and behaviors with humans.

Effects of Vasoactive Intestinal Peptide on Prolactin Secretion in Three Species of Passerine Birds

Previous work on domesticated species has indicated that vasoactive intestinal peptide (VIP) is an important prolactin-releasing factor in these birds, but no comparative work in passerine birds has been reported. This study showed that iv injections of VIP (50–100 μg/kg body mass) result in a dramatic, but transitory, rise in plasma prolactin in Mexican jays (Aphelocoma ultramarina). Significant increases in prolactin were also observed following VIP injection in blue jays (Cyanocitta cristata) and zebra finches (Poephilla guttata). At the dosage we used, maximum levels of prolactin attained were slightly lower (Mexican jays) or very similar (blue jay and zebra finch) to the maximum prolactin levels observed in other, breeding birds of the same species. In zebra finches that initially had low prolactin, VIP injection resulted in a greater than 10-fold increase in prolactin within 10 min, but those individuals that already had elevated prolactin showed no further increase in response to VIP. Slow-release pellets of VIP implanted subcutaneously in Mexican jays and releasing 10 or 15 μg VIP/day (two or three pellets) produced a significant increase in plasma prolactin (78 and 92% rise, respectively) compared to birds with placebo pellets or with with one pellet releasing only 5 μg/day.

Bird Communities in Riparian Buffer Strips of Industrial Forests

Retention of riparian buffers is a common management practice used to protect streams from the effects of upslope forest harvest. We compared bird use of riparian buffers along main stem rivers, tributary streams, and reference riparian zones having intact, upslope forests. Community composition differed considerably between buffers and references, and also between main stems and tributaries. Density of the more common species (those detected >20 times) was significantly higher along main stems than along tributaries. Four species (bay-breasted warbler, black-throated green warbler, blue jay, Cape May warbler) were more abundant along main stems than along tributaries; no species was more abundant along tributaries. The overall density of less common species was significantly higher in buffer strips than in reference sites, but four of the more common species (bay-breasted, blackburnian, black-throated green, and Cape May warblers) were more abundant in reference sites than in buffer strips. We did not detect differences in species diversity or richness among the different site types, but edge-species were significantly more common in buffer strips than in reference sites. Interior-species, in contrast, were significantly more common in reference sites.

The effect of background cuing on prey detection

Studies of prey detection have typically focused on how search image affects the capture of cryptic items. This study also considers how background vegetation influences cryptic prey detection. Blue jays,Cyanocitta cristata, searched digitized images for twoCatocalamoths:C.ilia, which is cryptic on oak, andC.relicta, which is cryptic on birch. Some images contained moths while others did not. The ability of blue jays to detect prey during repeated presentations of one prey type within a session was compared with their performance during randomly alternating presentations of both prey types within a session to examine search-image formation under two background conditions (informative and ambiguous). In the informative background condition, both trees in the image were of the same species and therefore, the background was a reliable indicator of which prey type might be present. In the ambiguous background condition, there was one tree of each species in the image and either prey type could be present. The results indicate that: (1) a search-image effect was observed only for the more cryptic prey type and only when the background was informative; (2) as accuracy on prey images (those with moths) increased, response latency remained unchanged; (3) performance on nonprey images (those without moths) was primarily determined by the difficulty of searching the background and not by the prey type in the accompanying prey images; and (4) search-image effects disappeared with extended practice. These results suggest that the ability to detect prey is influenced by background and that the presence of either multiple backgrounds or multiple prey types interferes with search-image formation.

Apostatic selection by blue jays produces balanced polymorphism in virtual prey

Apostatic selection, in which predators overlook rare prey types while consuming an excess of abundant ones, has been assumed to contribute to the maintenance of prey polymorphisms1,2,3. Such an effect requires predators to respond to changes in the relative abundance of prey, switching to alternatives when a focal prey type becomes less common4,5. Apostatic selection has often been investigated using fixed relative proportions of prey1,6, but its effects on predator–prey dynamics have been difficult to demonstrate7. Here we report results from a new technique that incorporates computer-generated displays8,9 into an established experimental system, that of blue jays (Cyanocitta cristata) hunting for cryptic Catocala moths10. Digital prey images from a virtual population are presented to predators. The relative numbers that escape detection determine the subsequent abundance of each prey type. If apostatic selection does promote stability, the system should converge on an eqlibrium in which each prey type appears at a characteristic abundance. Our results show that the detection of cryptic prey does involve apostatic selection, and that such selection can function to maintain prey polymorphism.

Nest predator distribution among clearcut forest, forest edge and forest interior in an extensively forested landscape

The distribution of avian and mammalian nest predator species in clearcut forest, forest edge and forest interior habitats was assessed on four study plots in 1992 and 1993 using line transect counts. Red squirrels ( Tamiasciurus hudsonicus) and eastern chipmunks ( Tamias striatus) were detected more often than expected by chance in mature forest than clearcut forest ( P<0.05). Linear regressions of sciurid abundance incorporating conifer basal area and distance from clearcut borders explained 75% and 60% of the variation in the abundance of red squirrels and eastern chipmunks, respectively; however, the regression equation of eastern chipmunk abundance was only marginally significant ( P=0.07). Abundance of blue jays ( Cyanocitta cristata) did not differ between clearcuts and mature forest ( P>0.05) and was not significantly correlated with conifer basal area or distance from clearcut borders ( P>0.05). We conclude that the distribution of two important nest predator species, the eastern chipmunk and the red squirrel, are primarily influenced by the distribution of conifers. However, the distribution of eastern chipmunks and red squirrels are affected by clearcut borders as well.

Mycoplasma sturni from blue jays and northern mockingbirds with conjunctivitis in Florida.

Northern mockingbirds (Mimus polyglottos) and blue jays (Cyanocitta cristata) in a Florida (USA) wildlife care facility developed clinical signs and gross lesions suggestive of the ongoing outbreak of Mycoplasma gallisepticum (MG) conjunctivitis in house finches (Carpodacus mexicanus) and American goldfinches (Carduelis tristis). Mycoplasmal organisms were cultured from conjunctival/corneal swabs of birds with sinusitis, conjunctivitis, and/or epiphora. All of the isolates tested were identified as Mycoplasma sturni by indirect immunofluorescence. Mycoplasma sturni as well as MG should be considered in the differential diagnosis of songbirds with conjunctivitis.

Physiology of Helping in Florida Scrub-Jays

If you are in the right habitat in south central Florida, you can frequently watch groups of Florida scrub-jays. If you make a hissing sound?a tech nique that birders call pishing?you might attract half a dozen of these birds, which resemble the common blue jay in size and shape, minus the crest. The blue wings and tail combined with a mostly blue head, a gray-brown triangular cape on a blue-gray back and a streaked blue-gray necklace, or breast band, identify the scrub-jay The pishing calls in the birds from the local territory, where they work together to raise offspring, an approach called co operative breeding. In cooperatively breeding species, one or more helpers assist a breeding pair in rearing young. Alexander Skutch, an American who has observed birds in Costa Rica for more than 50 years, first described cooperative breeding in 1935. Since then, the overwhelming majority of research in this field has examined

Rural and suburban forest edges: effect on egg predators and nest predation rates

Although the observed declines of many species of Neotropical migratory birds have been linked to losses in the wintering grounds, it is important to examine sources of mortality from all portions of the annual cycle to fully understand migratory bird declines. Forest fragmentation and the creation of new forest edges have been implicated as factors contributing to increased nest predation rates on the breeding grounds. We selected four forests with edges in suburban settings, and four forests with edges in rural settings, to determine if nest predation rates differed with human density. From 1993 to 1994 we used two types of automatic photographic systems and artificial nests baited with quail eggs to measure predation rates on ground- and shrub nests at points 20–420 m from the forest edges. Rural-edged forests experienced significantly higher nest predation rates than did suburban-edged forests. Only three species, blue jay, raccoon, and black bear, were responsible for virtually all of the predation events. While blue jays appeared to be unaffected by forest edge type, there were more bear predations in rural-edged forests and more raccoon predations in suburban-edged forests. There were no significant differences in predation rate between nest types or in species-specific rates of predation on the two nest types. We suggest that future studies of nest predation include the identification of predators to give scientists greater insight into the predation process.

Nut Caching by Blue Jays (Cyanocitta cristata L.): Implications for Tree Demography

-We examined jay caching patterns over 3 yr in a woodland-prairie landscape in S-central Iowa. Three aspects were examined: jay habitat preferences for caching, jay caching patterns before and after fire, and the influence of predation on nuts by small mammals on tree recruitment in jay territories. Blue jays cached nuts in a wide range of habitats, from open, grassy patches to mature forest. Jays cached preferentially in regenerating woodland and edge habitats while usually avoiding grassland habitats. Caching increased in grassland following a controlled burn. Detection by small mammals of artificial nut caches placed by the investigator was extremely

Edge-Related Nest Losses in Wisconsin Pine Barrens

Predation of artificial nests in pine barrens savanna patches in northwestern Wisconsin was correlated significantly with proximity to edge (P = 0.02). Densities of blue jays (Cyanocitta cristata) and brown-headed cowbirds (Molothrus ater) were significantly greater along edge transects than savanna interior transects (P < 0.001 and P = 0.001). Land management practices in the pine barrens may influence edge-related nest loss.