Andrea R. Norris

Mountain Pine Beetle Presence Affects Nest Patch Choice of Red-Breasted Nuthatches

Abstract The mountain pine beetle (Dendroctonus ponderosae) outbreak in western Canada poses significant conservation concern; thus, insights into its effects on wildlife habitat are essential. We used generalized linear mixed models to examine the influence of quaking aspen (Populus tremuloides) and mountain pine beetle–infected lodgepole pine (Pinus contortus) on nest patch selection of red-breasted nuthatches (Sitta canadensis) in central British Columbia, Canada. Prior to the outbreak, nuthatches selected nest patches with 64% more suitable nest trees (standing dead aspen, ≥12.5 cm dbh) than available (103 trees/ha vs. 63 trees/ha, respectively), but in outbreak years nuthatches chose nest patches with 37% more beetle-infected pine trees than available (63 trees/ha vs. 46 trees/ha, respectively). Our results suggest that nuthatches select sites that maximize nesting and foraging opportunities and, during food pulses, may trade off higher densities of suitable nest trees for higher densities of foraging trees.

Evidence for tolerance of parasitism in a tropical cavity-nesting bird, planalto woodcreeper (Dendrocolaptes platyrostris), in northern Argentina

Avian hosts may either resist the negative effects of nestling ectoparasites by minimizing the number of parasites, or tolerate parasitism by increasing their fecundity via the reproductive compensation hypothesis. Little is known about the interactions between ectoparasites and their avian hosts in the tropics. We (1) examined nestling developmentrates,andtestedwhether(2)parasitismbyasubcutaneousectoparasiticbotfly(Philornissp.)hadnegative effects on the condition of nestlings, and (3) these negative effects were minimized in larger broods in a tropical cavity- nesting bird, the planalto woodcreeper (Dendrocolaptes platyrostris), in primary and secondary Atlantic forests in the northern province of Misiones, Argentina. Nestling mass and ectoparasite load per nestling reached maxima when nestlings(n=50)werebetween10and14dold.Generallinearmixedmodelspredictedthatmassatfledgingdeclined withincreasingnestlingparasiteload,suggestingthatbotflieshadanegativeinfluenceonfledgingcondition.Parasite load per nestling declined with increasing brood size indicating that woodcreepers that increase their reproductive outputminimizethenegativeeffectsofparasitism.Overallwefoundevidencetosupportthetoleranceviareproductive compensationhypothesis.Futuretestsofthereproductivecompensationhypothesismayhelpdeterminetheunderlying mechanism of the observed negative correlation between parasite load of nestlings and brood size.

Red-Breasted Nuthatches (Sitta canadensis) Increase Cavity Excavation in Response to a Mountain Pine Beetle (Dendroctonus ponderosae) Outbreak

Abstract: In cavity-nesting vertebrate species, reproduction is limited by the production and availability of tree cavities. Excavating species may create new cavities to exploit food resource pulses in novel habitats, but availability of nesting resources may be constrained with increases in population densities. Over a 15-y period, we monitored the reproduction of cavity nesters and a large-scale mountain pine beetle (Dendroctonus ponderosae) outbreak that killed all mature lodgepole pine (Pinus contorta var. latifolia), at 30 mixed coniferous—deciduous stands in interior British Columbia, Canada. We examined how the probability of excavation of a bark insectivorous, facultative cavity excavator, the red-breasted nuthatch (Sitta canadensis), was influenced by mountain pine beetle abundance and changes in population densities of conspecific individuals and a nest predator, red squirrel (Tamiasciurus hudsomcus). Nuthatches always chose trembling aspen (Populus tremuloides) for nesting regardless of densities of nuthatch nests and availability of beetle-decayed pine as alternate nest trees. The number of nuthatch nests increased in years of increasing densities of beetle-infected pine, and the proportion of freshly excavated nests varied annually, increasing with the beetle outbreak from 26% of all cavities used in 2001 to 70% in 2002 and then declining after the outbreak to 17% in 2009. For each unit increase in densities per hectare of both nuthatches and beetle-infected pine trees, the odds that individuals would excavate a new cavity rather than use an existing cavity increased by 147 times. With each 10 m farther into the coniferous forest interior, the odds of excavation increased by 10 times. These results suggest that facultative excavators are able to exploit novel habitats during insect outbreaks by adjusting their nest-site selection patterns and increasing excavation, but that resource pulses may lead to limitation of nesting resources.

Nest boxes increase reproductive output for Tree Swallows in a forest grassland matrix in central British Columbia

Secondary cavity-nesting birds depend on tree cavities for nesting and roosting, but many studies of these birds are conducted using nest boxes. Implementation of effective conservation strategies for cavity-nesting species such as nest-site supplementation requires careful comparisons of fecundity and other vital rates for birds using both natural and artificial nest site types. We compared breeding phenology, clutch and brood sizes, and fledging success of Tree Swallows (Tachycineta bicolor) nesting in tree cavities and nest boxes during 2001–2003 in British Columbia, Canada. Swallows using nest boxes initiated egg-laying and hatched young at approximately the same time as those in tree cavities (2 June, 23 June, respectively). Female Tree Swallows in boxes laid larger clutches (5.9 ± 0.9 eggs, N = 76) than those in tree cavities (4.2 ± 1.6 eggs, N = 67). The mean number of nestlings hatched was greater in nest boxes (5.2 ± 1.1 nestlings, N = 67) than in tree cavities (2.6 ± 2.0 nestlings, N = 58). Pairs in boxes were over twice as successful in producing fledglings (93.4%; 57 of 61 pairs fledged > 1 young) than those in tree cavities (35.8%; 19 of 53 pairs). Of those successful nests, pairs nesting in boxes fledged 5.1 ± 1.1 young (N = 57), whereas those in tree cavities fledged 3.5 ± 1.2 young (N = 18). Because cavities in nest boxes averaged 60% larger in volume and 1.8 cm wider internally than tree cavities, we suggest that increased reproductive output was correlated with boxes enabling a larger clutch size. In previous research, we found that Tree Swallows were a poor competitor with other cavity-nesting passerines for tree cavities. The addition of nest boxes may serve as an effective way to supplement local reproduction for secondary cavity-nesting bird populations by reducing competition for limited nest sites. This is especially true in regions where the availability of natural nesting sites is highly variable, and where species compete with many other cavity-nesting passerines using a similar ecological niche and nesting cavities.